[Federal Register Volume 76, Number 169 (Wednesday, August 31, 2011)]
[Rules and Regulations]
[Pages 54294-54343]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-21359]
[[Page 54293]]
Vol. 76
Wednesday,
No. 169
August 31, 2011
Part II
Environmental Protection Agency
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40 CFR Parts 50, 53 and 58
Review of National Ambient Air Quality Standards for Carbon Monoxide;
Final Rule
Federal Register / Vol. 76 , No. 169 / Wednesday, August 31, 2011 /
Rules and Regulations
[[Page 54294]]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Parts 50, 53 and 58
[EPA-HQ-OAR-2008-0015; FRL-9455-2]
RIN 2060-AI43
Review of National Ambient Air Quality Standards for Carbon
Monoxide
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: This rule is being issued at this time as required by a court
order governing the schedule for completion of this review of the air
quality criteria and the national ambient air quality standards (NAAQS)
for carbon monoxide (CO). Based on its review, the EPA concludes the
current primary standards are requisite to protect public health with
an adequate margin of safety, and is retaining those standards. After
review of the air quality criteria, EPA further concludes that no
secondary standard should be set for CO at this time. EPA is also
making changes to the ambient air monitoring requirements for CO,
including those related to network design, and is updating, without
substantive change, aspects of the Federal reference method.
DATES: This final rule is effective on October 31, 2011.
ADDRESSES: EPA has established a docket for this action under Docket ID
No. EPA-HQ-OAR-2008-0015. Incorporated into this docket is a separate
docket established for the 2010 Integrated Science Assessment for
Carbon Monoxide (Docket ID No. EPA-HQ-ORD-2007-0925. All documents in
these dockets are listed on the http://www.regulations.gov Web site.
Although listed in the docket index, some information is not publicly
available, e.g., confidential business information (CBI) or other
information whose disclosure is restricted by statute. Certain other
material, such as copyrighted material, is not placed on the Internet
and will be publicly available for viewing at the Public Reading Room.
Abstracts of scientific studies cited in the review are also available
on the Internet at EPA's HERO Web site: http://hero.epa.gov/, by
clicking on the box on the right side of the page labeled ``Search
HERO.'' Publicly available docket materials are available
electronically through www.regulations.gov or may be viewed at the
Public Reading Room at the Air and Radiation Docket and Information
Center, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW.,
Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30
p.m., Monday through Friday, excluding legal holidays. The telephone
number for the Public Reading Room is (202) 566-1744 and the telephone
number for the Air and Radiation Docket and Information Center is (202)
566-1742.
FOR FURTHER INFORMATION CONTACT: Dr. Deirdre Murphy, Health and
Environmental Impacts Division, Office of Air Quality Planning and
Standards, Mail code C504-06, U.S. Environmental Protection Agency,
Research Triangle Park, NC 27711; telephone number: 919-541-0729; fax
number: 919-541-0237; e-mail address: [email protected]. For
further information specifically with regard to section IV of this
notice, contact Mr. Nealson Watkins, Air Quality Analysis Division,
Office of Air Quality Planning and Standards, Mail code C304-06, U.S.
Environmental Protection Agency, Research Triangle Park, NC 27711;
telephone number: 919-541-5522; fax number: 919-541-1903; e-mail
address: [email protected].
SUPPLEMENTARY INFORMATION:
Table of Contents
The following topics are discussed in this preamble:
I. Background
A. Legislative Requirements
B. Related Carbon Monoxide Control Programs
C. Review of the Air Quality Criteria and Standards for Carbon
Monoxide
D. Summary of Proposed Decisions on Standards for Carbon
Monoxide
E. Organization and Approach to Final Decisions on Standards for
Carbon Monoxide
II. Rationale for Decisions on the Primary Standards
A. Introduction
1. Overview of Air Quality Information
2. Overview of Health Effects Information
a. Carboxyhemoglobin as Biomarker of Exposure and Toxicity
b. Nature of Effects and At-Risk Populations
c. Cardiovascular Effects
3. Overview of Human Exposure and Dose Assessment
B. Adequacy of the Current Primary Standards
1. Rationale for Proposed Decision
2. Comments on Adequacy
3. Conclusions Concerning Adequacy of the Primary Standards
III. Consideration of a Secondary Standard
A. Introduction
B. Rationale for Proposed Decision
C. Comments on Consideration of Secondary Standard
D. Conclusions Concerning a Secondary Standard
IV. Amendments to Ambient Monitoring Requirements
A. Monitoring Methods
1. Proposed Changes to Parts 50 and 53
2. Public Comments
3. Decisions on Methods
B. Network Design
1. Proposed Changes
2. Public Comments
a. Near-Road Monitoring and Collocation With Near-Road Nitrogen
Dioxide Monitors
b. Population Thresholds for Requiring Near-Road Carbon Monoxide
Monitors
c. Implementation Schedule
d. Siting Criteria
e. Area-Wide Monitoring
f. Regional Administrator Authority
3. Conclusions on the Network Design
V. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
B. Paperwork Reduction Act
C. Regulatory Flexibility Act
D. Unfunded Mandates Reform Act
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health and Safety Risks
H. Executive Order 13211: Actions That Significantly Affect
Energy Supply, Distribution or Use
I. National Technology Transfer and Advancement Act
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
K. Congressional Review Act References
I. Background
A. Legislative Requirements
Two sections of the Clean Air Act (CAA) govern the establishment
and revision of the NAAQS. Section 108 (42 U.S.C. 7408) directs the
Administrator to identify and list certain air pollutants and then to
issue air quality criteria for those pollutants. The Administrator is
to list those air pollutants that in her ``judgment, cause or
contribute to air pollution which may reasonably be anticipated to
endanger public health or welfare;'' ``the presence of which in the
ambient air results from numerous or diverse mobile or stationary
sources;'' and ``for which * * * [the Administrator] plans to issue air
quality criteria * * * '' Air quality criteria are intended to
``accurately reflect the latest scientific knowledge useful in
indicating the kind and extent of all identifiable effects on public
health or welfare which may be expected from the presence of [a]
pollutant in the ambient air * * *'' 42 U.S.C. 7408(b). Section 109 (42
U.S.C. 7409) directs the Administrator to propose and promulgate
``primary'' and ``secondary'' NAAQS for pollutants for which air
[[Page 54295]]
quality criteria are issued. Section 109(b)(1) defines a primary
standard as one ``the attainment and maintenance of which in the
judgment of the Administrator, based on such criteria and allowing an
adequate margin of safety, are requisite to protect the public
health.'' \1\ A secondary standard, as defined in section 109(b)(2),
must ``specify a level of air quality the attainment and maintenance of
which, in the judgment of the Administrator, based on such criteria, is
requisite to protect the public welfare from any known or anticipated
adverse effects associated with the presence of [the] pollutant in the
ambient air.'' \2\
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\1\ The legislative history of section 109 indicates that a
primary standard is to be set at ``the maximum permissible ambient
air level * * * which will protect the health of any [sensitive]
group of the population,'' and that for this purpose ``reference
should be made to a representative sample of persons comprising the
sensitive group rather than to a single person in such a group'' S.
Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970).
\2\ Welfare effects as defined in section 302(h) (42 U.S.C.
7602(h)) include, but are not limited to, ``effects on soils, water,
crops, vegetation, man-made materials, animals, wildlife, weather,
visibility and climate, damage to and deterioration of property, and
hazards to transportation, as well as effects on economic values and
on personal comfort and well-being.''
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The requirement that primary standards provide an adequate margin
of safety was intended to address uncertainties associated with
inconclusive scientific and technical information available at the time
of standard setting. It was also intended to provide a reasonable
degree of protection against hazards that research has not yet
identified. See Lead Industries Association v. EPA, 647 F.2d 1130, 1154
(DC Cir. 1980), cert. denied, 449 U.S. 1042 (1980); American Petroleum
Institute v. Costle, 665 F.2d 1176, 1186 (DC Cir. 1981), cert. denied,
455 U.S. 1034 (1982); American Farm Bureau Federation v. EPA, 559 F.3d
512, 533 (DC Cir. 2009); Association of Battery Recyclers v. EPA, 604
F.3d 613, 617-18 (DC Cir. 2010). Both kinds of uncertainties are
components of the risk associated with pollution at levels below those
at which human health effects can be said to occur with reasonable
scientific certainty. Thus, in selecting primary standards that provide
an adequate margin of safety, the Administrator is seeking not only to
prevent pollution levels that have been demonstrated to be harmful but
also to prevent lower pollutant levels that may pose an unacceptable
risk of harm, even if the risk is not precisely identified as to nature
or degree. The CAA does not require the Administrator to establish a
primary NAAQS at a zero-risk level or at background concentration
levels, see Lead Industries v. EPA, 647 F.2d at 1156 n.51, but rather
at a level that reduces risk sufficiently so as to protect public
health with an adequate margin of safety.
In addressing the requirement for an adequate margin of safety, the
EPA considers such factors as the nature and severity of the health
effects involved, the size of sensitive population(s) at risk, and the
kind and degree of the uncertainties that must be addressed. The
selection of any particular approach to providing an adequate margin of
safety is a policy choice left specifically to the Administrator's
judgment. See Lead Industries Association v. EPA, 647 F.2d at 1161-62;
Whitman v. American Trucking Associations, 531 U.S. 457, 495 (2001).
In setting primary and secondary standards that are ``requisite''
to protect public health and welfare, respectively, as provided in
section 109(b), EPA's task is to establish standards that are neither
more nor less stringent than necessary for these purposes. In so doing,
EPA may not consider the costs of implementing the standards. See
generally, Whitman v. American Trucking Associations, 531 U.S. 457,
465-472, 475-76 (2001). Likewise, ``[a]ttainability and technological
feasibility are not relevant considerations in the promulgation of
national ambient air quality standards.'' American Petroleum Institute
v. Costle, 665 F. 2d at 1185.
Section 109(d)(1) requires that ``not later than December 31, 1980,
and at 5-year intervals thereafter, the Administrator shall complete a
thorough review of the criteria published under section 108 and the
national ambient air quality standards * * * and shall make such
revisions in such criteria and standards and promulgate such new
standards as may be appropriate. * * *'' Section 109(d)(2) requires
that an independent scientific review committee ``shall complete a
review of the criteria * * * and the national primary and secondary
ambient air quality standards * * * and shall recommend to the
Administrator any new * * * standards and revisions of existing
criteria and standards as may be appropriate. * * *'' Since the early
1980's, this independent review function has been performed by the
Clean Air Scientific Advisory Committee (CASAC).\3\
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\3\ Lists of CASAC members and of members of the CASAC CO Review
Panel are available at: http://yosemite.epa.gov/sab/sabproduct.nsf/WebCASAC/CommitteesandMembership?OpenDocument.
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B. Related Carbon Monoxide Control Programs
States are primarily responsible for ensuring attainment and
maintenance of ambient air quality standards once EPA has established
them. Under section 110 of the Act, and related provisions, states are
to submit, for EPA approval, state implementation plans (SIPs) that
provide for the attainment and maintenance of such standards through
control programs directed to sources of the pollutants involved. The
states, in conjunction with EPA, also administer the prevention of
significant deterioration program. See CAA sections 160-169. In
addition, Federal programs provide for nationwide reductions in
emissions of these and other air pollutants through the Federal motor
vehicle and motor vehicle fuel control program under title II of the
Act (CAA sections 202-250), which involves controls for emissions from
moving sources and controls for the fuels used by these sources and new
source performance standards for stationary sources under section 111.
C. Review of the Air Quality Criteria and Standards for Carbon Monoxide
EPA initially established NAAQS for CO on April 30, 1971. The
primary standards were established to protect against the occurrence of
carboxyhemoglobin levels in human blood associated with health effects
of concern. The standards were set at 9 parts per million (ppm), as an
8-hour average, and 35 ppm, as a 1-hour average, neither to be exceeded
more than once per year (36 FR 8186). In the 1971 decision, the
Administrator judged that attainment of these standards would provide
the requisite protection of public health with an adequate margin of
safety and would also provide requisite protection against known and
anticipated adverse effects on public welfare, and accordingly set the
secondary (welfare-based) standards identical to the primary (health-
based) standards.
In 1985, EPA concluded its first periodic review of the criteria
and standards for CO (50 FR 37484). In that review, EPA updated the
scientific criteria upon which the initial CO standards were based
through the publication of the 1979 Air Quality Criteria Document for
Carbon Monoxide (AQCD; USEPA, 1979a) and prepared a Staff Paper (USEPA,
1979b), which, along with the 1979 AQCD, served as the basis for the
development of the notice of proposed rulemaking which was published on
August 18, 1980 (45 FR 55066). Delays due to uncertainties
[[Page 54296]]
regarding the scientific basis for the final decision resulted in EPA's
announcing a second public comment period (47 FR 26407). Following
substantial reexamination of the scientific data, EPA prepared an
Addendum to the 1979 AQCD (USEPA, 1984a) and an updated Staff Paper
(USEPA, 1984b). Following review by CASAC (Lippmann, 1984), EPA
announced its decision not to revise the existing primary standards and
to revoke the secondary standard for CO on September 13, 1985, due to a
lack of evidence of effects on public welfare at ambient concentrations
(50 FR 37484).
On August 1, 1994, EPA concluded its second periodic review of the
criteria and standards for CO by deciding that revisions to the CO
NAAQS were not warranted at that time (59 FR 38906). This decision
reflected EPA's review of relevant scientific information assembled
since the last review, as contained in the 1991 AQCD (USEPA, 1991) and
the 1992 Staff Paper (USEPA, 1992). Thus, the primary standards were
retained at 9 ppm with an 8-hour averaging time, and 35 ppm with a 1-
hour averaging time, neither to be exceeded more than once per year (59
FR 38906).
EPA initiated the next periodic review in 1997 and released the
final 2000 AQCD (USEPA, 2000) in August 2000. After release of the
AQCD, Congress requested that the National Research Council (NRC)
review the impact of meteorology and topography on ambient CO
concentrations in high altitude and extreme cold regions of the U.S.
The NRC convened the Committee on Carbon Monoxide Episodes in
Meteorological and Topographical Problem Areas, which focused on
Fairbanks, Alaska, as a case-study.
A final report, ``Managing Carbon Monoxide Pollution in
Meteorological and Topographical Problem Areas,'' was published in 2003
(NRC, 2003) and offered a wide range of recommendations regarding
management of CO air pollution, cold start emissions standards,
oxygenated fuels, and CO monitoring. Following completion of the NRC
report, EPA did not conduct rulemaking to complete the review.
On September 13, 2007, EPA issued a call for information from the
public (72 FR 52369) requesting the submission of recent scientific
information on specified topics. On January 28-29, 2008, a workshop was
held to discuss policy-relevant scientific and technical information to
inform EPA's planning for the CO NAAQS review (73 FR 2490). Following
the workshop, a draft Integrated Review Plan (IRP) (USEPA, 2008a) was
made available in March 2008 for public comment and was discussed by
the CASAC via a publicly accessible teleconference consultation on
April 8, 2008 (73 FR 12998; Henderson, 2008). EPA made the final IRP
available in August 2008 (USEPA, 2008b).
In preparing the Integrated Science Assessment for Carbon Monoxide
(ISA or Integrated Science Assessment), EPA held an authors'
teleconference in November 2008 with invited scientific experts to
discuss preliminary draft materials prepared as part of the ongoing
development of the CO ISA and its supplementary annexes. The first
draft ISA (USEPA, 2009a) was made available for public review on March
12, 2009 (74 FR 10734), and reviewed by CASAC at a meeting held on May
12-13, 2009 (74 FR 15265). A second draft ISA (USEPA, 2009b) was
released for CASAC and public review on September 23, 2009 (74 FR
48536), and it was reviewed by CASAC at a meeting held on November 16-
17, 2009 (74 FR 54042). The final ISA was released in January 2010
(USEPA, 2010a).
In May 2009, OAQPS released a draft planning document, the draft
Scope and Methods Plan (USEPA, 2009c), for consultation with CASAC and
public review at the CASAC meeting held on May 12-13, 2009. Taking into
consideration comments on the draft Scope and Methods Plan from CASAC
(Brain, 2009) and the public, OAQPS staff developed and released for
CASAC review and public comment a first draft Risk and Exposure
Assessment (REA) (USEPA, 2009d), which was reviewed at the CASAC
meeting held on November 16-17, 2009. Subsequent to that meeting and
taking into consideration comments from CASAC (Brain and Samet, 2010a)
and public comments on the first draft REA, a second draft REA (USEPA,
2010d) was released for CASAC review and public comment in February
2010, and reviewed at a CASAC meeting held on March 22-23, 2010.
Drawing from information in the final CO ISA and the second draft REA,
EPA released a draft Policy Assessment (PA) (USEPA, 2010e) in early
March 2010 for CASAC review and public comment at the same meeting.
Taking into consideration comments on the second draft REA and the
draft PA from CASAC (Brain and Samet, 2010b, 2010c) and the public,
staff completed the quantitative assessments which are presented in the
final REA (USEPA, 2010b). Staff additionally took into consideration
those comments and the final REA analyses in completing the final
Policy Assessment (USEPA, 2010c) which was released in October 2010.
The proposed decision (henceforth ``proposal'') on the review of
the CO NAAQS was signed on January 28, 2011, and published in the
Federal Register on February 11, 2011. The EPA held a public hearing to
provide direct opportunity for oral testimony by the public on the
proposal. The hearing was held on February 28, 2011, in Arlington,
Virginia. At this public hearing, EPA heard testimony from five
individuals representing themselves or specific interested
organizations. Transcripts from this hearing and written testimony
provided at the hearing are in the docket for this review.
Additionally, written comments were received from various commenters
during the public comment period on the proposal. Significant issues
raised in the public comments are discussed in the preamble of this
final action. A summary of all other significant comments, along with
EPA's responses (henceforth ``Response to Comments'') can be found in
the docket for this review.
The schedule for completion of this review is governed by a court
order resolving a lawsuit filed in March 2003 by a group of plaintiffs
who alleged that EPA had failed to perform its mandatory duty, under
section 109(d)(1), to complete a review of the CO NAAQS within the
period provided by statute. The court order that governs this review,
entered by the court on November 14, 2008, and amended on August 30,
2010, provides that EPA will sign for publication a notice of final
rulemaking concerning its review of the CO NAAQS no later than August
12, 2011.
Some commenters have referred to and discussed individual
scientific studies on the health effects of CO that were not included
in the ISA (USEPA, 2010a) (``'new' studies''). In considering and
responding to comments for which such ``new'' studies were cited in
support, EPA has provisionally considered the cited studies in the
context of the findings of the ISA.
As in prior NAAQS reviews, EPA is basing its decision in this
review on studies and related information included in the ISA, REA and
Policy Assessment, which have undergone CASAC and public review. The
studies assessed in the ISA and Policy Assessment, and the integration
of the scientific evidence presented in them, have undergone extensive
critical review by EPA, CASAC, and the public. The rigor of that review
makes these studies, and their integrative assessment, the most
reliable source of scientific information on which to base decisions on
the NAAQS, decisions that all parties recognize as of great import.
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NAAQS decisions can have profound impacts on public health and welfare,
and NAAQS decisions should be based on studies that have been
rigorously assessed in an integrative manner not only by EPA but also
by the statutorily mandated independent advisory committee, as well as
the public review that accompanies this process. EPA's provisional
consideration of these studies did not and could not provide that kind
of in-depth critical review.
This decision is consistent with EPA's practice in prior NAAQS
reviews and its interpretation of the requirements of the CAA. Since
the 1970 amendments, the EPA has taken the view that NAAQS decisions
are to be based on scientific studies and related information that have
been assessed as a part of the pertinent air quality criteria, and has
consistently followed this approach. This longstanding interpretation
was strengthened by new legislative requirements enacted in 1977, which
added section 109(d)(2) of the Act concerning CASAC review of air
quality criteria. See 71 FR 61144, 61148 (October 17, 2006) (final
decision on review of NAAQS for particulate matter) for a detailed
discussion of this issue and EPA's past practice.
As discussed in EPA's 1993 decision not to revise the NAAQS for
ozone, ``new'' studies may sometimes be of such significance that it is
appropriate to delay a decision on revision of a NAAQS and to
supplement the pertinent air quality criteria so the studies can be
taken into account (58 FR at 13013-13014, March 9, 1993). In the
present case, EPA's provisional consideration of ``new'' studies
concludes that, taken in context, the ``new'' information and findings
do not materially change any of the broad scientific conclusions
regarding the health effects and exposure pathways of ambient CO made
in the air quality criteria. For this reason, reopening the air quality
criteria review would not be warranted even if there were time to do so
under the court order governing the schedule for this rulemaking.
Accordingly, EPA is basing the final decisions in this review on
the studies and related information included in the CO air quality
criteria that have undergone CASAC and public review. EPA will consider
the ``new'' studies for purposes of decision-making in the next
periodic review of the CO NAAQS, which EPA expects to begin soon after
the conclusion of this review and which will provide the opportunity to
fully assess these studies through a more rigorous review process
involving EPA, CASAC, and the public. Further discussion of these
``new'' studies can be found in the Response to Comments document.
D. Summary of Proposed Decisions on Standards for Carbon Monoxide
For reasons discussed in the notice of proposed rulemaking, the
Administrator proposed to retain the current primary CO standards. With
regard to consideration of a secondary standard, the Administrator
proposed to conclude that no secondary standards should be set at this
time.
E. Organization and Approach to Final Decisions on Standards for Carbon
Monoxide
This action presents the Administrator's final decisions in this
review of the CO standards. Decisions regarding the primary CO
standards are addressed below in section II. Consideration of a
secondary CO standard is addressed below in section III. Ambient
monitoring methods and network design related to implementation of the
CO standards are addressed below in section IV. A discussion of
statutory and executive order reviews is provided in section V.
Today's final decisions are based on a thorough review in the
Integrated Science Assessment of the latest scientific information on
known and potential human health and welfare effects associated with
exposure to CO in the environment. These final decisions also take into
account: (1) Assessments in the Policy Assessment of the most policy-
relevant information in the Integrated Science Assessment as well as
quantitative exposure, dose and risk assessments based on that
information presented in the Risk and Exposure Assessment; (2) CASAC
Panel advice and recommendations, as reflected in its letters to the
Administrator and its discussions of drafts of the Integrated Science
Assessment, Risk and Exposure Assessment and Policy Assessment at
public meetings; (3) public comments received during the development of
these documents, either in connection with CASAC Panel meetings or
separately; and (4) public comments received on the proposed
rulemaking.
II. Rationale for Decisions on the Primary Standards
A. Introduction
This section presents the rationale for the Administrator's
decision that the current primary standards are requisite to protect
public health with an adequate margin of safety, and that they should
be retained. In developing this rationale, EPA has drawn upon an
integrative synthesis in the Integrated Science Assessment of the
entire body of evidence published through mid-2009 on human health
effects associated with the presence of CO in the ambient air. The
research studies evaluated in the ISA have undergone intensive scrutiny
through multiple layers of peer review, with extended opportunities for
review and comment by the CASAC Panel and the public. As with virtually
any policy-relevant scientific research, there is uncertainty in the
characterization of health effects attributable to exposure to ambient
CO. While important uncertainties remain, the review of the health
effects information has been extensive and deliberate. In the judgment
of the Administrator, this intensive evaluation of the scientific
evidence provides an adequate basis for regulatory decision making at
this time. This review also provides important input to EPA's research
plan for improving our future understanding of the relationships
between exposures to ambient CO and health effects.
The health effects information and quantitative exposure/dose
assessment were summarized in sections II.B and II.C of the proposal
(76 FR at 8162-8172) and are only briefly outlined in sections II.A.2
and II.A.3 below. Responses to public comments specific to the material
presented in sections II.A.1 through II.A.3 below are provided in the
Response to Comments document.
Subsequent sections of this preamble provide a more complete
discussion of the Administrator's rationale, in light of key issues
raised in public comments, for concluding that the current standards
are requisite to protect public health with an adequate margin of
safety and that it is appropriate to retain the current primary CO
standards to continue to provide requisite public health protection
(section II.B).
1. Overview of Air Quality Information
This section briefly summarizes the information on CO sources,
emissions, ambient air concentrations and aspects of associated
exposure presented in section II.A of the proposal, as well as in
section 1.3 of the Policy Assessment and chapter 2 of the Risk and
Exposure Assessment.
Carbon monoxide in ambient air is formed by both natural and
anthropogenic processes. In areas of human activity such as urban
areas, it is formed primarily by the incomplete combustion of carbon-
containing fuels with the combustion conditions influencing the rate of
formation. For example, as a result of the combustion
[[Page 54298]]
conditions, CO emissions from large fossil-fueled power plants are
typically very low because optimized fuel consumption conditions make
boiler combustion highly efficient. In contrast, internal combustion
engines used in many mobile sources have widely varying operating
conditions. As a result, higher and more varying CO formation results
from the operation of mobile sources, which continue to be a
significant source sector for CO in ambient air (ISA, sections 3.4 and
3.5; 2000 AQCD, section 7.2; REA, section 2.2 and 3.1.3).
Mobile sources are a substantial contributor to total CO emissions,
particularly in urban areas (ISA, section 3.5.1.3; REA, section 3.1.3).
Highest ambient concentrations in urban areas occur on or near
roadways, particularly highly travelled roadways, and decline somewhat
steeply with distance (ISA, section 3.5.1.3; REA, section 3.1.3;
Baldauf et al., 2008a,b; Zhu et al., 2002). For example, as described
in the ISA, a study by Zhu et al., (2002) documented CO concentrations
at an interstate freeway to be ten times as high as an upwind
monitoring site; concentrations declined rapidly in the downwind
direction to levels only approximately one half roadway concentrations
within 100 to 300 meters (ISA, section 3.5.1.3, Figure 3-29; Zhu et
al., 2002). Factors that can influence the steepness of the gradient
include wind direction and other meteorological variables, and on-road
vehicle density (ISA, section 3.5.1.3, Figures 3-29 and 3-30; Zhu et
al., 2002; Baldauf et al., 2008a, b). These traffic-related ambient
concentrations contribute to the higher short-term ambient CO exposures
experienced near busy roads and particularly in vehicles, as described
in more detail in the REA and PA.
2. Overview of Health Effects Information
This section summarizes information presented in section II.B of
the proposal pertaining to health endpoints associated with the range
of exposures considered to be most relevant to current ambient CO
exposure levels. In recognition of the use of an internal biomarker in
evaluating health risk for CO, the following section summarizes key
aspects of the use of carboxyhemoglobin as an internal biomarker
(section II.A.2.a). This is followed first by a summary of the array of
CO-induced health effects and recognition of at-risk subpopulations
(section II.A.2.b) and then by a summary of the evidence regarding
cardiovascular effects (section II.A.2.c).
a. Carboxyhemoglobin as Biomarker of Exposure and Toxicity
This section briefly summarizes the current state of knowledge, as
described in the Integrated Science Assessment, of the role of
carboxyhemoglobin in mediating toxicity and as a biomarker of exposure.
The section also summarizes the roles of endogenously produced CO and
exposure to ambient and nonambient CO in influencing internal CO
concentrations and carboxyhemoglobin (COHb) levels.
At this time, as during past reviews, the best characterized
mechanism of action of CO is tissue hypoxia caused by binding of CO to
hemoglobin to form COHb in the blood (e.g., USEPA, 2000; USEPA, 1991;
ISA). Increasing levels of COHb in the blood stream with subsequent
decrease in oxygen availability for organs and tissues are of concern
in people who have compromised compensatory mechanisms (e.g., lack of
capacity to increase blood flow in response to hypoxia), such as those
with pre-existing heart disease. For example, the integrative review of
health effects of CO indicates that ``the clearest evidence indicates
that individuals with CAD [coronary artery disease] are most
susceptible to an increase in CO-induced health effects'' (ISA, section
5.7.8).
Carboxyhemoglobin is formed in the blood both from CO originating
in the body (endogenous CO) \4\ and from CO that has been inhaled into
the body (exogenous CO).\5\ The amount of COHb that occurs in the blood
depends on factors specific to both the physiology of the individual
(including disease state) and the exposure circumstances. These include
factors associated with an individual's rate of COHb elimination and
production of endogenous CO, as well as those that influence the intake
of exogenous CO into the blood, such as the differences in CO
concentration (and partial pressure) in inhaled air, exhaled air, and
blood; duration of a person's exposure to changed CO concentrations in
air; and exertion level or inhalation rate (ISA, chapter 4).
---------------------------------------------------------------------------
\4\ Endogenous CO is produced from biochemical reactions
associated with normal breakdown of heme proteins (ISA, section
4.5).
\5\ Exogenous CO includes CO emitted to ambient air, CO emitted
to ambient air that has infiltrated indoors and CO that originates
indoors from sources such as gas stoves, tobacco smoke and gas
furnaces (ISA, section 3.6; REA, section 2.2).
---------------------------------------------------------------------------
Apart from the impairment of oxygen delivery to tissues related to
COHb formation, toxicological studies also indicate several other
pathways by which CO acts in the body, which involve a wide range of
molecular targets and internal CO concentrations (2000 AQCD, sections
5.6-5.9; ISA, section 5.1.3). The role of these alternative less-well-
characterized mechanisms in CO-induced health effects at concentrations
relevant to the current NAAQS, however, is not clear. New research
based on this evidence is needed to further understand these pathways
and their linkage to CO-induced effects in susceptible populations.
Accordingly, COHb level in blood continues to be well recognized and
most commonly used as an important internal dose metric, and is
supported by the evidence as the most useful indicator of CO exposure
that is related to CO health effects of major concern (ISA, p. 2-4,
sections 4.1, 4.2, 5.1.1; 1991 AQCD; 2000 AQCD; 2010 ISA).
b. Nature of Effects and At-Risk Populations
The long-standing body of evidence that has established many
aspects of the biological effects of CO continues to contribute to our
understanding of the health effects of ambient CO (PA, section 2.2.1).
Inhaled CO elicits various health effects through binding to, and
associated alteration of the function of, a number of heme-containing
molecules, mainly hemoglobin (see e.g., ISA, section 4.1). The best
characterized health effect associated with CO levels of concern is
decreased oxygen availability to critical tissues and organs,
specifically the heart, induced by increased COHb levels in blood (ISA,
section 5.1.2). Consistent with this, medical conditions that affect
the biological mechanisms which compensate for this effect (e.g.,
vasodilation and increased coronary blood flow with increased oxygen
delivery to the myocardium) can contribute to a reduced amount of
oxygen available to key body tissues, potentially affecting organ
system function and limiting exercise capacity (2000 AQCD, section
7.1).\6\
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\6\ For example, people with peripheral vascular diseases and
heart disease patients often have markedly reduced circulatory
capacity and reduced ability to compensate for increased circulatory
demands during exercise and other stress (2000 AQCD, p. 7-7).
---------------------------------------------------------------------------
This evidence newly available in this review provides additional
detail and support to our prior understanding of CO effects and
population susceptibility. In this review, the clearest evidence for
ambient CO-related effects is available for cardiovascular effects.
Using an established framework to characterize the evidence as to
likelihood of causal relationships between exposure to ambient CO and
[[Page 54299]]
specific health effects (ISA, chapter 1), the ISA states that ``Given
the consistent and coherent evidence from epidemiologic and human
clinical studies, along with biological plausibility provided by CO's
role in limiting oxygen availability, it is concluded that a causal
relationship is likely to exist between relevant short-term CO
exposures and cardiovascular morbidity'' (ISA, p. 2-6, section 2.5.1).
Using the same established framework, the ISA describes the evidence as
suggestive of causal relationships between relevant ambient CO exposure
and several other health effects: Relevant short- and long-term CO
exposures and central nervous system (CNS) effects, birth outcomes and
developmental effects following long-term exposure, respiratory
morbidity following short-term exposure, and mortality following short-
term exposure (ISA, section 2.5). However, there is only limited
evidence for these relationships, and the current body of evidence
continues to indicate cardiovascular effects, particularly effects
related to the role of CO in limiting oxygen availability to tissues,
as those of greatest concern at low exposures with relevance to ambient
concentrations (ISA, chapter 2). The evidence for these effects is
further described in section II.A.2.c below.
As described in the proposal, the terms susceptibility,
vulnerability, sensitivity, and at-risk are commonly employed in
identifying population groups or life stages at relatively higher risk
for health risk from a specific pollutant. In the ISA for this review,
the term susceptibility has been used broadly to recognize populations
that have a greater likelihood of experiencing effects related to
ambient CO exposure, with use of the term susceptible populations, as
used in the ISA, defined as follows (ISA, section 5.7, p. 5-115):
Populations that have a greater likelihood of experiencing
health effects related to exposure to an air pollutant (e.g., CO)
due to a variety of factors including, but not limited to: Genetic
or developmental factors, race, gender, lifestage, lifestyle (e.g.,
smoking status and nutrition) or preexisting disease, as well as
population-level factors that can increase an individual's exposure
to an air pollutant (e.g., CO) such as socioeconomic status [SES],
which encompasses reduced access to health care, low educational
attainment, residential location, and other factors.
Thus, susceptible populations are at greater risk of CO effects and are
also referred to as at-risk in the summary below.
As described in the proposal, the population with pre-existing
cardiovascular disease continues to be the best-characterized
population at risk of adverse CO-induced effects, with CAD recognized
as ``the most important susceptibility characteristic for increased
risk due to CO exposure'' (ISA, section 2.6.1). An important factor
determining the increased susceptibility of this population is their
inability to compensate for the reduction in tissue oxygen levels due
to an already compromised cardiovascular system. Individuals with a
healthy cardiovascular system (i.e., with healthy coronary arteries)
have operative physiologic compensatory mechanisms (e.g., increased
blood flow and oxygen extraction) for CO-induced tissue hypoxia and are
unlikely to be at increased risk of CO-induced effects (ISA, p. 2-
10).\7\ In addition, the high oxygen consumption of the heart, together
with the inability to compensate for tissue hypoxia, makes the cardiac
muscle of a person suffering from CAD a critical target for CO.
---------------------------------------------------------------------------
\7\ The other well-studied individuals at the time of the last
review were healthy male adults that experienced decreased exercise
duration at similar COHb levels during short term maximal exercise.
This population was of lesser concern since it represented a smaller
sensitive group, and potentially limited to individuals that would
engage in vigorous exercise such as competing athletes (1991 AQCD,
section 10.3.2).
---------------------------------------------------------------------------
Thus, the current evidence continues to support the identification
of people with cardiovascular disease as susceptible to CO-induced
health effects (ISA, 2-12) and those having CAD as the population with
the best-characterized susceptibility (ISA, sections 5.7.1.1 and
5.7.8).\8\ An important susceptibility consideration for this
population is the inability to compensate for CO-induced hypoxia since
individuals with CAD have an already compromised cardiovascular system.
This population includes those with angina pectoris (cardiac chest
pain), those who have experienced a heart attack, and those with silent
ischemia or undiagnosed ischemic heart disease (AHA, 2003). People with
other cardiovascular diseases, particularly heart diseases, are also at
risk of CO-induced health effects.
---------------------------------------------------------------------------
\8\ As recognized in the ISA, ``Although the weight of evidence
varies depending on the factor being evaluated, the clearest
evidence indicates that individuals with CAD are most susceptible to
an increase in CO-induced health effects'' (ISA, p. 2-12).
---------------------------------------------------------------------------
Cardiovascular disease comprises many types of medical disorders,
including heart disease, cerebrovascular disease (e.g., stroke),
hypertension (high blood pressure), and peripheral vascular diseases.
Heart disease, in turn, comprises several types of disorders, including
ischemic heart disease (coronary heart disease [CHD] or CAD, myocardial
infarction, angina), congestive heart failure, and disturbances in
cardiac rhythm (2000 AQCD, section 7.7.2.1).\9\ Other types of
cardiovascular disease may also contribute to increased susceptibility
to the adverse effects of low levels of CO (ISA, section 5.7.1.1). For
example, evidence with regard to other types of cardiovascular disease
such as congestive heart failure, arrhythmia, and non-specific
cardiovascular disease, and more limited evidence for peripheral
vascular and cerebrovascular disease, indicates that ``the continuous
nature of the progression of CAD and its close relationship with other
forms of cardiovascular disease suggest that a larger population than
just those individuals with a prior diagnosis of CAD may be susceptible
to health effects from CO exposure'' (ISA, p. 5-117).
---------------------------------------------------------------------------
\9\ Coronary artery disease (CAD), often also called coronary
heart disease or ischemic heart disease, is a category of
cardiovascular disease associated with narrowed heart arteries.
Individuals with this disease may have myocardial ischemia, which
occurs when the heart muscle receives insufficient oxygen delivered
by the blood. Exercise-induced angina pectoris (chest pain) occurs
in many of them. Among all patients with diagnosed CAD, the
predominant type of ischemia, as identified by electrocardiogram ST
segment depression, is asymptomatic (i.e., silent). Patients who
experience angina typically have additional ischemic episodes that
are asymptomatic (2000 AQCD, section 7.7.2.1). In addition to such
chronic conditions, CAD can lead to sudden episodes, such as
myocardial infarction (ISA, p. 5-24).
---------------------------------------------------------------------------
As described in the proposal, several other populations are
potentially at risk of CO-induced effects, including: Those with other
pre-existing diseases that may already have limited oxygen
availability, increased COHb levels or increased endogenous CO
production, such as people with obstructive lung diseases, diabetes and
anemia; older adults; fetuses during critical phases of development and
young infants or newborns; those who spend a substantial time on or
near heavily traveled roadways; visitors to high-altitude locations;
and people ingesting medications and other substances that enhance
endogenous or metabolic CO formation (ISA, section 2.6.1). While the
evidence suggests a potential susceptibility of these populations,
information characterizing susceptibility for these groups is limited.
For example, information is lacking on specific CO exposures or COHb
levels that may be associated with health effects in these other groups
and the nature of those effects, as well as a way to relate the
specific evidence
[[Page 54300]]
available for the CAD population to these other populations (PA,
section 2.2.1).
c. Cardiovascular Effects
Similar to the previous review, results from controlled human
exposure studies of individuals with coronary artery disease (CAD)
(Adams et al., 1988; Allred et al., 1989a, 1989b, 1991; Anderson et
al., 1973; Kleinman et al., 1989, 1998; Sheps et al., 1987\10\) are the
``most compelling evidence of CO-induced effects on the cardiovascular
system'' (ISA, section 5.2). Additionally, the use of an internal dose
metric, COHb, adds to the strength of the findings in these controlled
exposure studies. As a group, these studies demonstrate the role of
short-term CO exposures in increasing the susceptibility of people with
CAD to incidents of exercise-associated myocardial ischemia.
---------------------------------------------------------------------------
\10\ Statistical analyses of the data from Sheps et al., (1987)
by Bissette et al. (1986) indicate a significant decrease in time to
onset of angina at 4.1% COHb if subjects that did not experience
exercise-induced angina during air exposure are also included in the
analyses.
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Among the controlled human exposure studies, the ISA places
principal emphasis on the study of CAD patients by Allred et al.
(1989a, 1989b, 1991) \11\ (which was also considered in the previous
review) for the following reasons: (1) Dose-response relationships were
observed; (2) effects were observed at the lowest COHb levels tested
(mean of 2-2.4% COHb \12\ following experimental CO exposure), with no
evidence of a threshold; (3) objective measures of myocardial ischemia
(ST-segment depression) \13\ were assessed, as well as the subjective
measure of decreased time to induction of angina; (4) measurements were
taken both by CO-oximetry (CO-Ox) and by gas chromatography (GC), which
provides a more accurate measurement of COHb blood levels \14\; (5) a
large number of study subjects were used; (6) a strict protocol for
selection of study subjects was employed to include only CAD patients
with reproducible exercise-induced angina; and (7) the study was
conducted at multiple laboratories around the U.S. This study evaluated
changes in time to exercise-induced onset of markers of myocardial
ischemia resulting from two short (approximately 1-hour) CO exposures
targeted to result in mean study subject COHb levels of 2% and 4%,
respectively (ISA, section 5.2.4). In this study, subjects (n = 63) on
three separate occasions underwent an initial graded exercise treadmill
test, followed by 50 to 70-minute exposures under resting conditions to
room air CO concentrations or CO concentrations targeted for each
subject to achieve blood COHb levels of 2% and 4%. The exposures were
to average CO concentrations of 0.7 ppm (room air concentration range
0-2 ppm), 117 ppm (range 42-202 ppm) and 253 ppm (range 143-357 ppm).
After the 50- to 70-minute exposures, subjects underwent a second
graded exercise treadmill test, and the percent change in time to onset
of angina and time to ST endpoint between the first and second exercise
tests was determined. For the two CO exposures, the average post-
exposure COHb concentrations were reported as 2.4% and 4.7%, and the
subsequent post-exercise average COHb concentrations were reported as
2.0% and 3.9%.\15\
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\11\ Other controlled human exposure studies of CAD patients
(listed in Table 2-2 of the PA, and discussed in more detail in the
1991 and 2000 AQCDs) similarly provide evidence of reduced time to
exercise-induced angina associated with elevated COHb resulting from
controlled short-duration exposure to increased concentrations of
CO.
\12\ These levels and other COHb levels described for this study
below are based on gas chromatography analysis unless otherwise
specified. Matched measurements available for CO-oximetry (CO-Ox)
and gas chromatography (GC) in this study indicate CO-Ox
measurements of 2.65% (post-exercise mean) and 3.21% (post-exposure
mean) corresponding to the GC measurement levels of 2.00% (post-
exercise mean) to 2.38% (post-exposure mean) for the lower exposure
level assessed in this study (Allred et al., 1991).
\13\ The ST-segment is a portion of the electrocardiogram,
depression of which is an indication of insufficient oxygen supply
to the heart muscle tissue (myocardial ischemia). Myocardial
ischemia can result in chest pain (angina pectoris) or such
characteristic changes in ECGs or both. In individuals with coronary
artery disease, it tends to occur at specific levels of exercise.
The duration of exercise required to demonstrate chest pain and/or a
1-mm change in the ST segment of the ECG were key measurements in
the multicenter study by Allred et al. (1989a, 1989b, 1991).
\14\ As stated in the ISA, the gas chromatographic technique for
measuring COHb levels ``is known to be more accurate than
spectrophotometric measurements, particularly for samples containing
COHb concentrations < 5%'' (ISA, p. 5-41). CO-oximetry is a
spectrophotometric method commonly used to rapidly provide
approximate concentrations of COHb during controlled exposures (ISA,
p. 5-41). At the low concentrations of COHb (< 5%) more relevant to
ambient CO exposures, co-oximeters are reported to overestimate COHb
levels compared to GC measurements, while at higher concentrations,
this method is reported to produce underestimates (ISA, p. 4-18).
\15\ While the COHb blood level for each subject during the
exercise tests was intermediate between the post-exposure and
subsequent post-exercise measurements (e.g., mean 2.4-2.0% and 4.7-
3.9%), the study authors noted that the measurements at the end of
the exercise test represented the COHb concentrations at the
approximate time of onset of myocardial ischemia as indicated by
angina and ST segment changes. The corresponding ranges of CO-Ox
measurements for the two exposures were 2.7-3.2% and 4.7-5.6%. In
this document, we refer to the GC-measured mean of 2.0% or 2.0-2.4%
for the COHb levels resulting from the lower experimental CO
exposure.
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Across all subjects, the mean time to angina onset for control
(``room'' air) exposures was approximately 8.5 minutes, and the mean
time to ST endpoint was approximately 9.5 minutes (Allred et al.,
1989b). Relative to room-air exposure that resulted in a mean COHb
level of 0.6% (post-exercise), exposures to CO resulting in post-
exercise mean COHb concentrations of 2.0% and 3.9% were observed to
decrease the exercise time required to induce ST-segment depression by
5.1% (p = 0.01) and 12.1% (p < 0.001), respectively. These changes were
well correlated with the onset of exercise-induced angina, the time to
which was shortened by 4.2% (p = 0.027) and 7.1% (p = 0.002),
respectively, for the two experimental CO exposures (Allred et al.,
1989a, 1989b, 1991).\16\ As at the time of the last review, while ST-
segment depression is recognized as an indicator of myocardial
ischemia, the exact physiological significance of the observed changes
among those with CAD is unclear (ISA, p. 5-48).
---------------------------------------------------------------------------
\16\ Another indicator measured in the study was the combination
of heart rate and systolic blood pressure which provides a clinical
index of the work of the heart and myocardial oxygen consumption,
since heart rate and blood pressure are major determinants of
myocardial oxygen consumption (Allred et al., 1991). A decrease in
oxygen to the myocardium would be expected to be paralleled by
ischemia at lower heart rate and systolic blood pressure. This heart
rate-systolic blood pressure indicator at the time to ST-endpoint
was decreased by 4.4% at the 3.9% COHb dose level and by a
nonstatistically-significant, smaller amount at the 2.0% COHb dose
level.
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No controlled human exposure studies have been specifically
designed to evaluate the effect of controlled short-term exposures to
CO resulting in COHb levels lower than a study mean of 2% (ISA, section
5.2.6). However, an important finding of the multi-laboratory study was
the dose-response relationship observed between COHb and the markers of
myocardial ischemia, with effects observed at the lowest increases in
COHb tested, without evidence of a measurable threshold effect. As
reported by the authors, the results comparing ``the effects of
increasing COHb from baseline levels (0.6%) to 2 and 3.9% COHb showed
that each produced further changes in objective ECG measures of
ischemia'' implying that ``small increments in COHb could adversely
affect myocardial function and produce ischemia'' (Allred et al.,
1989b, 1991).
The epidemiological evidence has expanded considerably since the
last review including numerous additional studies that are coherent
with the evidence on markers of myocardial
[[Page 54301]]
ischemia from controlled human exposure studies of CAD patients (ISA,
section 2.7). The most recent set of epidemiological studies in the
U.S. have evaluated the associations between ambient concentrations of
multiple pollutants (i.e., fine particles or PM2.5, nitrogen
dioxide, sulfur dioxide, ozone, and CO) at fixed-site ambient monitors
and increases in emergency department visits and hospital admissions
for specific cardiovascular health outcomes including ischemic heart
disease (IHD), myocardial infarction, congestive heart failure (CHF),
and cardiovascular diseases (CVD) as a whole (Bell et al., 2009; Koken
et al., 2003; Linn et al., 2000; Mann et al., 2002; Metzger et al.,
2004; Symons et al., 2006; Tolbert et al., 2007; Wellenius et al.,
2005). As noted by the ISA, ``[s]tudies of hospital admissions and
[emergency department] visits for IHD provide the strongest
[epidemiological] evidence of ambient CO being associated with adverse
CVD outcomes'' (ISA, p. 5-40, section 5.2.3). With regard to studies
for other measures of cardiovascular morbidity, the ISA notes that
``[t]hough not as consistent as the IHD effects, the effects for all
CVD hospital admissions (which include IHD admissions) and CHF hospital
admissions also provide evidence for an association of cardiovascular
outcomes and ambient CO concentrations'' (ISA, section 5.2.3). While
noting the difficulty in determining the extent to which CO is
independently associated with CVD outcomes in this group of studies as
compared to CO as a marker for the effects of another traffic-related
pollutant or mix of pollutants, the ISA concludes that the
epidemiological evidence, particularly when considering the copollutant
analyses, provides support to the clinical evidence for a direct effect
of short-term ambient CO exposure on CVD morbidity (ISA, pp. 5-40 to 5-
41).
3. Overview of Human Exposure and Dose Assessment
Our consideration of the scientific evidence in the current review,
as at the time of the last review, is informed by results from a
quantitative analysis of estimated population exposure and resultant
COHb levels. This analysis provides estimates of the percentages of
simulated at-risk populations expected to experience daily maximum COHb
levels at or above a range of benchmark levels under varying air
quality scenarios (e.g., just meeting the current or alternative
standards), as well as characterizations of the kind and degree of
uncertainties inherent in such estimates. The benchmark COHb levels
were identified based on consideration of the evidence discussed in
section II.A.2 above. In this section, we provide a short overview of
key aspects of the assessment conducted for this review. The assessment
is summarized more fully in section II.C of the proposal, discussed in
detail in the REA and summarized in the PA (section 2.2.2). The results
of the analyses as they relate to considerations of the adequacy of the
current standards are discussed in section II.B.3 below.
As noted in the proposal notice, people can be exposed to CO in
ambient air when they are outdoors and also when they are in indoor
locations into which ambient (outdoor) air has infiltrated (ISA,
sections 3.6.1 and 3.6.5). Indoor locations may also contain CO from
indoor sources, such as gas stoves and tobacco smoke. Where present,
these indoor sources can be important contributors to total CO exposure
and can contribute to much greater CO exposures and associated COHb
levels than those associated with ambient sources (ISA, section
3.6.5.2). For example, indoor source-related exposures, such as faulty
furnaces or other combustion appliances, have been estimated in the
past to lead to COHb levels on the order of twice as high as short-term
elevations in ambient CO that were more likely to be encountered by the
general public (2000 AQCD, p. 7-4). Further, some exposure/dose
assessments performed for previous reviews have included modeling
simulations both without and with indoor (nonambient) sources (gas
stoves and tobacco smoke) to provide context for the assessment of
ambient CO exposure and dose (e.g., USEPA, 1992; Johnson et al., 2000),
and these assessments have found that nonambient sources have a
substantially greater impact on the highest total exposures and COHb
levels experienced by the simulated population than do ambient sources
(Johnson et al., 2000; REA, sections 1.2 and 6.3). While recognizing
this potential for indoor sources, where present, to play a role in CO
exposures and COHb levels, the exposure modeling in the current review
(described below) did not include indoor CO sources in order to focus
on the impact of ambient CO on population COHb levels.
The assessment estimated ambient CO exposure and associated COHb
levels in simulated at-risk populations in two urban study areas in
Denver and Los Angeles, in which current ambient CO concentrations are
below the current standards. Estimates were developed for exposures to
ambient CO associated with current ``as is'' conditions (2006 air
quality) and also for higher ambient CO concentrations associated with
air quality conditions simulated to just meet the current 8-hour
standard,\17\ as well as for air quality conditions simulated to just
meet several potential alternative standards. Although we consider it
unlikely that air concentrations in many urban areas across the U.S.
that are currently well below the current standards would increase to
just meet the 8-hour standard, we recognize the potential for CO
concentrations in some areas currently below the standard to increase
to just meet the standard. We additionally recognize that this
simulation can provide useful information in evaluating the current
standard, although we recognize the uncertainty associated with
simulating this hypothetical profile of higher CO concentrations that
just meet the current 8-hour standard.
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\17\ As noted elsewhere, the 8-hour standard is the controlling
standard for ambient CO concentrations.
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The exposure and dose modeling for the assessment, presented in
detail in the REA, relied on version 4.3 of EPA's Air Pollutant
Exposure model (APEX4.3), which estimates human exposure using a
stochastic, event-based microenvironmental approach (REA, chapter 4).
The review of the CO standards completed in 1994 relied on population
exposure and dose estimates generated from the probabilistic NAAQS
exposure model (pNEM), a model that, among other differences from the
current modeling approach with APEX4.3, employed a cohort-based
approach (Johnson et al., 1992; USEPA, 1992).18 19 Each of
the model developments since the use of pNEM in that review have been
designed to allow APEX to better represent human behavior, human
physiology, and
[[Page 54302]]
microenvironmental concentrations and to more accurately estimate
variability in CO exposures and COHb levels (REA, chapter 4).\20\
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\18\ When using the cohort approach, each cohort is assumed to
contain persons with identical exposures during the specified
exposure period. Thus, variability in exposure will be attributed to
differences in how the cohorts are defined, not necessarily
reflecting differences in how individuals might be exposed in a
population. In the assessment for the review completed in 1994, a
total of 420 cohorts were used to estimate population exposure based
on selected demographic information (11 groups using age, gender,
work status), residential location, work location, and presence of
indoor gas stoves (Johnson, et al., 1992; USEPA, 1992).
\19\ The use of pNEM in the prior review also (1) relied on a
limited set of activity pattern data (approximately 3,600 person-
days), (2) used four broadly defined categories to estimate
breathing rates, and (3) implemented a geodesic distance range
methodology to approximate workplace commutes (Johnson et al., 1992;
USEPA, 1992). Each of these approaches used by pNEM, while
appropriate given the data available at that time, would tend to
limit the ability to accurately model expected variability in the
population exposure and dose distributions.
\20\ APEX4.3 includes new algorithms to (1) simulate
longitudinal activity sequences and exposure profiles for
individuals, (2) estimate activity-specific minute-by-minute oxygen
consumption and breathing rates, (3) address spatial variability in
home and work-tract ambient concentrations for commuters, and (4)
estimate event-based microenvironmental concentrations (PA, section
2.2.2).
---------------------------------------------------------------------------
As used in the current assessment, APEX probabilistically generates
a sample of hypothetical individuals from an actual population database
and simulates each individual's movements through time and space (e.g.,
indoors at home, inside vehicles) to estimate his or her exposure to
ambient CO (REA, chapter 4). Based on exposure concentrations, minute-
by-minute activity levels, and physiological characteristics of the
simulated individuals (see REA, chapters 4 and 5), APEX estimates the
level of COHb in the blood for each individual at the end of each hour
based on a nonlinear solution to the Coburn-Forster-Kane equation (REA,
section 4.4.7).
As discussed in section II.A.2.b above, people with cardiovascular
disease are the population of primary focus in this review, and, more
specifically, coronary artery disease, also known as coronary heart
disease, is the ``most important susceptibility characteristic for
increased risk due to CO exposure'' (ISA, p. 2-11). Controlled human
exposure studies have provided quantitative COHb dose-response
information for this specific population with regard to effects on
markers of myocardial ischemia. Accordingly, based on the current
evidence with regard to quantitative information of COHb levels and
association with specific health effects, the at-risk populations
simulated in the quantitative assessment were (1) adults with CHD (also
known as IHD or CAD), both diagnosed and undiagnosed, and (2) adults
with any heart diseases, including undiagnosed ischemia.\21\ Evidence
characterizing the nature of specific health effects of CO in other
populations is limited and does not include specific COHb levels
related to health effects in those groups. As a result, the
quantitative assessment does not develop separate quantitative dose
estimates for populations other than those with CHD or HD.
---------------------------------------------------------------------------
\21\ As described in section1.2 above, this is the same
population group that was the focus of the CO NAAQS exposure/dose
assessments conducted previously (e.g., USEPA, 1992; Johnson et al.,
2000).
---------------------------------------------------------------------------
APEX simulations performed for this review focused on exposures to
ambient CO occurring in eight microenvironments,\22\ absent any
contribution to microenvironment concentrations from indoor
(nonambient) CO sources. Previous assessments, that have included
modeling simulations both with and without certain indoor sources,
indicated that the impact of such sources can be substantial with
regard to the portion of the at-risk population experiencing higher
exposures and COHb levels (Johnson et al., 2000). While we are limited
with regard to information regarding CO emissions from indoor sources
today and how they may differ from the time of the 2000 assessment, we
note that ambient contributions have notably declined, and indoor
source contributions from some sources may also have declined. Thus, as
indicated in the Policy Assessment, we have no firm basis to conclude a
different role for indoor sources today with regard to contribution to
population CO exposure and COHb levels.
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\22\ The 8 microenvironments modeled in the REA comprised a
range of indoor and outdoor locations including residences as well
as motor vehicle-related locations such as inside vehicles, and
public parking and fueling facilities, where the highest exposures
were estimated (REA, sections 5.9 and 6.1).
---------------------------------------------------------------------------
In considering the REA dose estimates in the Policy Assessment,
staff considered estimates of the portion of the simulated at-risk
populations estimated to experience daily maximum end-of-hour absolute
COHb levels above identified benchmark levels (at least once and on
multiple occasions), as well as estimates of the percentage of
population person-days (the only metric available from the modeling for
the 1994 review), and also population estimates of daily maximum
ambient contribution to end-of-hour COHb levels.\23\ In identifying
COHb benchmark levels of interest, primary attention was given to the
multi-laboratory study in which COHb was analyzed by the more accurate
GC method (Allred et al., 1989a, 1989b, 1991) discussed in section
II.A.2.c above. As summarized in the proposal, the Policy Assessment
recognized distinctions between the REA ``baseline'' (arising from
prior ambient exposure and endogenous CO production) and the pre-
exposure COHb levels in the controlled human exposure study (arising
from ambient and nonambient exposure history, as well as from
endogenous CO production), and also noted the impact of ``baseline''
COHb levels on COHb levels occurring in response to short ambient CO
exposure events such as those simulated in the REA.
---------------------------------------------------------------------------
\23\ As summarized in the proposal and described more fully in
the REA and PA, absolute COHb refers to the REA estimates of COHb
levels resulting from endogenously produced CO and exposure to
ambient CO (in the absence of any nonambient sources). The
additional REA estimates of ambient CO exposure contribution to COHb
levels were calculated by subtracting COHb estimates obtained in the
absence of CO exposure--i.e., that due to endogenous CO production
alone (see REA, Appendix B.6)--from the corresponding end-of-hour
absolute COHb estimates for each simulated individual. Thus, the REA
reports estimates of the maximum end-of-hour ambient contributions
across the simulated year, in addition to the maximum absolute end-
of hour COHb levels.
---------------------------------------------------------------------------
Numerous improvements have been made over the last decade that have
reduced the uncertainties associated with the models used to estimate
COHb levels resulting from ambient CO exposures under different air
quality conditions, including those associated with just meeting the
current CO NAAQS (REA, section 4.3). This progression in exposure model
development has led to the model currently used by the agency
(APEX4.3), which has an enhanced capacity to estimate population CO
exposures and more accurately predicts COHb levels in persons exposed
to CO. Our application of APEX4.3 in this review, using updated data
and new algorithms to estimate exposures and doses experienced by
individuals, better represents the variability in population exposure
and COHb dose levels than the model version used in previous CO
assessments.\24\ However, while APEX 4.3 is greatly improved when
compared with previously used exposure models, its application is still
limited with regard to data to inform our understanding of spatial
relationships in ambient CO concentrations and within microenvironments
of particular interest. Further information regarding model
improvements and exposure modeling uncertainties is summarized in
section 2.2.2 of the Policy Assessment and described in detail in
chapter 7 of the REA.
---------------------------------------------------------------------------
\24\ APEX4.3 provides estimates for percent of population
projected to experience a single or multiple occurrences of a daily
maximum COHb level above the various benchmark levels, as well as
percent of person-days.
---------------------------------------------------------------------------
Taking into consideration improvements in the model algorithms and
data since the last review, and having identified and characterized
these uncertainties, the Policy Assessment concludes that the estimates
associated with the current analysis, at a minimum, better reflect the
full distribution of exposures and dose as compared to results from the
1992 analysis. As noted in the Policy Assessment, however, potentially
greater uncertainty remains in our characterization of the upper and
lower
[[Page 54303]]
percentiles of the distribution of population exposures and COHb dose
levels relative to that of other portions of the respective
distribution. When considering the overall quality of the current
exposure modeling approach, the algorithms, and the input data used,
alongside the identified limitations and uncertainties, the REA and
Policy Assessment conclude that the quantitative assessment provides
reasonable estimates of CO exposure and COHb dose for the simulated
population the assessment is intended to represent (i.e., the
population residing within the urban core of each study area). The
Policy Assessment additionally notes the impact on the REA dose
estimates for ambient CO contribution to COHb of the lack of nonambient
sources in the model simulations. This aspect of the assessment design
may contribute to higher estimates of the contribution of short-
duration ambient CO exposures to total COHb than would result from
simulations that include the range of commonly encountered CO sources
beyond just those contributing to ambient air CO concentrations.
Although the specific quantitative impact of this on estimates of
population percentages discussed in this document is unknown,
consideration of COHb estimates from the 2000 assessment indicates a
potential for the inclusion of nonambient sources to appreciably affect
absolute COHb (REA, section 6.3) and accordingly implies the potential,
where present, for an impact on overall ambient contribution to a
person's COHb level. Key results of the exposure and dose analyses were
presented in the Policy Assessment and summarized in the proposal
(Tables 1 and 2 of the proposal).
B. Adequacy of the Current Primary Standards
In considering the evidence and quantitative exposure and dose
estimates with regard to judgments on the adequacy afforded by the
current standards, the final decision is largely a public health policy
judgment. A final decision must draw upon scientific information and
analyses about health effects and risks, as well as judgments about how
to consider the range and magnitude of uncertainties that are inherent
in the scientific evidence and analyses. Our approach to informing
these judgments is based on the recognition that the available health
effects evidence generally reflects a continuum, consisting of ambient
levels at which scientists generally agree that health effects are
likely to occur, through lower levels at which the likelihood and
magnitude of the response become increasingly uncertain. This approach
is consistent with the requirements of the NAAQS provisions of the Act
and with how EPA and the courts have historically interpreted the Act.
These provisions require the Administrator to establish primary
standards that, in the Administrator's judgment, are requisite to
protect public health with an adequate margin of safety. In so doing,
the Administrator seeks to establish standards that are neither more
nor less stringent than necessary for this purpose. The Act does not
require that primary standards be set at a zero-risk level, but rather
at a level that avoids unacceptable risks to public health, including
the health of sensitive groups.\25\
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\25\ The sensitive population groups identified in a NAAQS
review may (or may not) be comprised of low income or minority
groups. Where low income/minority groups are among the sensitive
groups, the rulemaking decision will be based on providing
protection for these and other sensitive population groups. To the
extent that low income/minority groups are not among the sensitive
groups, a decision based on providing protection of the sensitive
groups would be expected to provide protection for the low income/
minority groups (as well as any other less sensitive population
groups).
---------------------------------------------------------------------------
In evaluating whether it is appropriate to revise the current CO
standards, the Administrator's considerations build on the general
approach used in the last review and reflect the broader body of
evidence and information now available. The approach used is based on
an integration of information on health effects associated with
exposure to ambient CO; expert judgment on the adversity of such
effects on individuals; and policy judgments as to when the standards
are requisite to protect public health with an adequate margin of
safety, which are informed by air quality and related analyses,
quantitative exposure and risk assessments when possible, and
qualitative assessment of impacts that could not be quantified. The
Administrator has taken into account both evidence-based and
quantitative exposure- and risk-based considerations in developing
conclusions on the adequacy of the current primary CO standards.
The Administrator's proposed conclusions on the adequacy of the
current primary standards are summarized below (section II.B.1),
followed by consideration of comments received on the proposal (section
II.B.2) and the Administrator's final decision with regard to the
adequacy of the current primary standards (II.B.3).
1. Rationale for Proposed Decision
At the time of the proposal, in considering the adequacy of the
current standards, the Administrator carefully considered the available
evidence and conclusions contained in the Integrated Science
Assessment; the information, exposure/dose assessment, rationale and
conclusions presented in the Policy Assessment; the advice and
recommendations from CASAC; and public comments as of that date. In so
doing, the Administrator noted the following: (1) The long-standing
evidence base concerning effects associated with exposure to CO,
including the key role played by hypoxia (reduced oxygen availability)
induced by increased COHb blood levels, and the use of COHb as the
bioindicator and dose metric for evaluating CO exposure and the
potential for health effects; (2) the strong evidence of cardiovascular
effects of short-term CO exposures including the evidence from
controlled human exposure studies that demonstrate a reduction in time
to onset of exercise-induced markers of myocardial ischemia in response
to increased COHb, and the health significance of responses observed at
the 2% COHb level induced by 1-hour CO exposure, as compared to higher
COHb levels; and (3) the identification of people with cardiovascular
disease as a key population at risk from short-term ambient CO
exposures. In the proposal, as at the time of the last review, the
Administrator additionally considered and took particular note of the
exposure and dose modeling results, recognizing key limitations and
uncertainties, and in light of judgments noted above regarding the
health significance of findings from the controlled human exposure
studies, placing less weight on the health significance of infrequent
or rare occurrences of COHb levels at or just above 2% and more weight
to the significance of repeated such occurrences, as well as
occurrences of higher COHb levels.
The Administrator also considered the newly available and much-
expanded epidemiological evidence, including the complexity associated
with quantitative interpretation of these studies with regard to CO,
particularly the few studies available in areas where the current
standards are met. Further, the Administrator considered the advice of
CASAC, including their overall agreement with the Policy Assessment
conclusion that the current evidence and quantitative exposure and dose
estimates provide support for retaining the current standards, their
view that, in
[[Page 54304]]
light of the epidemiological studies, revisions to lower the standards
should be considered and their preference for a lower standard, and
also their advice regarding the complications associated with
interpreting the epidemiological studies for CO. Although CASAC
expressed a preference for a lower standard, CASAC also indicated that
the current evidence provides support for retaining the current suite
of standards and CASAC's recommendations appear to recognize that their
preference for a lower standard was contingent on a judgment as to the
weight to be placed on the epidemiological evidence. For the reasons
explained in the proposal, after full consideration of CASAC's advice
and the epidemiological evidence, as well as its associated
uncertainties and limitations, the Administrator proposed to judge
those uncertainties and limitations to be too great for the
epidemiological evidence to provide a basis for revising the current
standards.
Taking all these considerations together, the Administrator
proposed to conclude that the current suite of standards provides a
very high degree of protection for the COHb levels and associated
health effects of concern, as indicated by the extremely low estimates
of occurrences, and provides slightly less but a still high degree of
protection for the effects associated with lower COHb levels, the
physiological significance of which is less clear. The Administrator
additionally proposed to conclude that consideration of the
epidemiological studies does not lead her to identify a need for any
greater protection. Thus, the Administrator proposed to conclude that
the current suite of standards provides an adequate margin of safety
against adverse effects associated with short-term ambient CO
exposures. For these and all of the reasons discussed above, and
recognizing the CASAC conclusion that, overall, the current evidence
and REA results provide support for retaining the current standards,
the Administrator proposed to conclude that the current suite of
primary CO standards is requisite to protect public health with an
adequate margin of safety from effects of ambient CO.
2. Comments on Adequacy
In considering comments on the adequacy of the current standards,
the Administrator first notes the advice and recommendations from
CASAC. In the context of CASAC's review of the documents prepared
during the course of the review, CASAC sent EPA five letters providing
advice regarding assessment and interpretation of the available
scientific evidence and the REA for the purposes of judging the
adequacy of the current CO standards (Brain and Samet, 2009; Brain and
Samet, 2010a; Brain and Samet, 2010b; Brain and Samet, 2010c; Brain and
Samet, 2010d). In conveying comments on the draft Policy Assessment,
CASAC agreed with the conclusion that the current evidence provides
support for retaining the current suite of standards, while they also
expressed a preference for a lower standard and stated that the
epidemiological evidence could indicate the occurrence of adverse
health effects at levels of the standards (Brain and Samet, 2010c).
With regard to the interpretation of epidemiological studies on CO,
CASAC's collective advice included recommendations regarding the weight
to be placed on the epidemiological evidence (Brain and Samet, 2010c),
as well as cautionary statements regarding interpretation of the
epidemiological studies. Such statements included the observation that
``[d]istinguishing the effects of CO per se from the consequences of CO
as a marker of pollution or vehicular traffic is a challenge, which
[the ISA] needs to confront as thoroughly as possible'' (Brain and
Samet, 2009, p. 2). In another letter CASAC further cautioned (Brain
and Samet, 2010d, p. 2):
The problem of co-pollutants serving as potential confounders is
particularly problematic for CO. Since exposure levels for CO are
now low, consideration needs to be given to the possibility that in
some situations CO may be a surrogate for exposure to a mix of
pollutants generated by fossil fuel combustion. A better
understanding of the possible role of co-pollutants is relevant to
regulation and to the design, analysis, and interpretation of
epidemiologic studies on the health effects of CO.
CASAC additionally noted concerns regarding the spatial coverage of the
existing CO monitoring network and the sensitivity of deployed monitors
(Brain and Samet, 2009; Brain and Samet, 2010a; Brain and Samet, 2010b;
Brain and Samet, 2010d). On a related note, they cautioned that
``[u]nderstanding the extent of exposure measurement error is critical
for evaluating epidemiological evidence'' (Brain and Samet, 2009).
General comments from the public based on relevant factors that
either support or oppose retention of the current primary CO standards
are addressed in this section. Other specific public comments related
to consideration of the adequacy of the current standards, as well as
general comments based on implementation-related factors that are not a
permissible basis for considering the need to revise the current
standards, are addressed in the Response to Comments document.
The public comments received on the proposal were divided with
regard to support for the Agency's proposed conclusion as to the
adequacy of the current standards. All of the state and local
environmental agencies or governments that provided comments on the
standards concurred with EPA's proposed conclusions as did the three
industry commenters. All of these commenters generally noted their
agreement with the rationale provided in the proposal, with some
additionally citing CASAC's recognition of support in the evidence for
the adequacy of the current standards. Some of these commenters noted
agreement with the weight given to the epidemiological studies in the
proposal and also noted the little change in exposure/risk estimates
since the time of the last review. One commenter additionally stated
their view that the REA overstates the exposure and risk associated
with the current standards.
As described in section II.B.3 below, the EPA generally agrees with
these commenters regarding the adequacy of the current CO standards and
with CASAC that the evidence provides support for the conclusion that
the current CO standards protect public health with an adequate margin
of safety. EPA additionally has given consideration to CASAC's advice
regarding interpretation of epidemiological evidence for CO,
recognizing the limitations associated with its use in drawing
quantitative interpretations regarding levels of ambient CO related to
health outcomes.
Two submissions recommending revision of the standards were
received from national environmental or public health organizations.
Additional submissions recommending revision were received from a
private consultant; a group of scientists, physicians, and others; and
a group of private citizens. In support of their position, these
commenters variously cited CASAC comments regarding emphasis to give
epidemiological studies and CASAC's stated preference for a lower
standard. These submissions generally disagreed with EPA's
consideration of the epidemiological evidence in the proposal and
recommended that EPA give greater emphasis to epidemiological studies
of a range of endpoints, including developmental and respiratory
effects, based on the commenters' view that the epidemiological studies
provided evidence of harm associated with ambient CO levels below the
current
[[Page 54305]]
standards and inadequate protection for sensitive populations. Among
these submissions, those that specified levels for revised standards
recommended levels that were no higher than the lowest part of the
ranges for the two standards that were identified for consideration in
the Policy Assessment and the example options that CASAC suggested for
inclusion in the Policy Assessment. Additionally, one commenter
described the view that the CO standards should be revised to levels at
or below the range of CO concentrations in exhaled breath of healthy
non-smokers.
EPA generally disagrees with these commenters regarding conclusions
that can be drawn from the evidence, including the epidemiological
studies, pertaining to the adequacy of the current CO standards. In
considering the adequacy of the current standards, it is important to
consider both the extent to which the evidence supports a causal
relationship between ambient CO exposures and adverse health effects,
as well as the extent to which there is evidence pertinent to such
effects under air quality conditions in which the current standards are
met. With regard to the latter point, and focusing on the
epidemiological evidence, it is the studies involving air quality
conditions in which the current standards were met that are most
informative in evaluating the adequacy of the standards (PA, p. 2-30).
We note that very few of the epidemiological studies observing an
association of cardiovascular disease-related outcomes with short-term
CO concentrations (or those observing associations for other health
effects) were conducted in areas that met the current standards
throughout the period of study, thus limiting their usefulness with
regard to judging the adequacy of the current standards (PA, pp. 2-33,
2-36).
Further, as CASAC has cautioned, ``the problem of co-pollutants
serving as potential confounders is particularly problematic for CO''
(Brain and Samet, 2010d). While some CO epidemiological studies have
applied the commonly used statistical method, two-pollutant regression
models, to inform conclusions regarding CO as the pollutant eliciting
the effects in these studies, and while, in some studies, the CO
associations remain robust after adjustment for another traffic
combustion-related pollutant, such as PM2.5 or nitrogen
dioxide (NO2) (PA, pp. 2-36 to 2-37), the potential exists
for there to be etiologically relevant pollutants that are correlated
with CO yet absent from the analysis, particularly given the many
pollutants associated with fossil fuel combustion. The CASAC
specifically recognized this potential in stating that ``consideration
needs to be given to the possibility that in some situations CO may be
a surrogate for exposure to a mix of pollutants generated by fossil
fuel combustion'' and ``a better understanding of the possible role of
co-pollutants is relevant to * * * the interpretation of epidemiologic
studies on the health effects of CO'' (Brain and Samet, 2010d).
In light of these issues related to potential confounding by co-
pollutants in the case of CO, uncertainty related to exposure error for
CO is of particular concern in quantitatively interpreting the
epidemiological evidence (e.g., with regard to ambient concentrations
contributing to health outcomes).\26\ As noted above, CASAC cautioned
the Agency on the importance of understanding the extent of exposure
error in evaluating the epidemiological evidence for CO (Brain and
Samet, 2009). There are two aspects to the epidemiological studies in
the specific case of CO (as contrasted with other pollutants such as PM
and NO2) that may contribute exposure error in the studies
(PA, pp. 2-34 to 2-38; 76 FR 8177-8178). The first relates to the
uncertainty associated with quantitative interpretation of the
epidemiological study results at low ambient concentrations in light of
the sizeable portion of ambient CO measurements that are at or below
monitor method detection limits (MDLs). As described in the proposal,
uncertainty related to the prevalence of ambient CO monitor
concentrations at or below MDLs is a greater concern for the more
recently available epidemiological studies in which the study areas
have much reduced ambient CO concentrations compared with those in the
past (PA, pp. 2-37 to 2-38). This complicates our interpretation of
specific ambient CO concentrations associated with health effects (ISA,
p. 3-91; Brain and Samet, 2010d), providing us with reduced confidence
in quantitative interpretations of epidemiological studies for CO.
Additionally, as described in the proposal, there is uncertainty and
potential error associated with exposure estimates in the CO
epidemiological studies that relate to the use of area-wide or central-
site monitor CO concentrations in light of information about the steep
gradient in CO concentrations with distance from source locations such
as highly-trafficked roadways (ISA, section 3.5.1.3). As a result of
differences in factors related to pollutant formation, this gradient is
steeper for CO than for other traffic combustion-related pollutants,
such as PM2.5 and NO2, contributing to a greater
potential for exposure misclassification in the case of CO by the
reliance on central site monitors in the CO epidemiological studies.
Thus, as noted in the proposal, we recognize that the expanded body of
epidemiological evidence available in this review includes its own set
of uncertainties which complicates its interpretation, particularly
with regard to ambient concentrations that may be eliciting health
outcomes.
---------------------------------------------------------------------------
\26\ In contrasting the strength of the epidemiological evidence
available for the 2000 AQCD with that in the current review, the ISA
notes that uncertainties identified in 2000 remain, including the
ability of community fixed-site monitors to represent spatially
variable ambient CO concentrations and personal exposures; the small
expected increase in COHb due to ambient CO concentrations; the lack
of biological plausibility for health effects to occur at such COHb
levels, even in diseased individuals; and the possibility that
ambient CO is serving as a surrogate for a mixture of combustion-
related pollutants. These uncertainties complicate the quantitative
interpretation of the epidemiologic findings, ``particularly
regarding the biological plausibility of health effects occurring at
COHb levels resulting from exposures to ambient CO concentrations
measured at AQS monitors'' (ISA, pp. 2-16 to 2-17).
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In our integrated assessment across all types of evidence in the
ISA for this review, we conclude that a causal relationship is likely
to exist for short-term exposures to ambient concentrations of CO and
cardiovascular morbidity. In reaching this conclusion, the ISA notes
that the most compelling evidence comes from the controlled human
exposure studies (ISA, p. 2-5), which also document a significant dose-
response relationship over a range of COHb concentrations relevant to
consideration of the NAAQS (ISA, p. 2-13). In considering the
epidemiological evidence for relevant cardiovascular outcomes, which
includes multiple studies reporting associations with ambient CO
concentrations under conditions when the current standards were not met
(PA, p. 2-30), the ISA notes that these studies are coherent with the
findings from the controlled human exposure studies (ISA, p. 2-17).
However, as summarized here, various aspects of the evidence complicate
quantitative interpretation of it with regard to ambient concentrations
that might be eliciting the reported health outcomes.
An additional complication to our consideration of the CO
epidemiological evidence is that, in contrast to the health effects
evidence for all other criteria pollutants, the epidemiological studies
for CO use a different exposure/dose metric from that which is the
focus of the broader health evidence base, and
[[Page 54306]]
additional information that might be used to bridge this gap is
lacking. In the case of CO, the epidemiological studies use air
concentration as the exposure/dose metric, while much of the broader
health effects evidence for CO, and particularly that related to
cardiovascular effects, demonstrates and focuses on an internal
biomarker of CO exposure (COHb) which has been considered a critical
key to CO toxicity.\27\ The strong evidence describing the role of COHb
in CO toxicity is important to consider in interpreting the CO
epidemiological studies and contributes to the biological plausibility
of the ischemia-related health outcomes that have been associated with
ambient CO concentrations. Yet, we do not have information on the COHb
levels of epidemiological study subjects that we can evaluate in the
context of the COHb levels eliciting health effects in the controlled
human exposure studies. Further, we lack additional information on the
CO exposures of the epidemiological study subjects to both ambient and
nonambient sources of CO that might be used to estimate their COHb
levels and bridge the gap between the two study types. Additionally the
ISA recognizes that the changes in COHb that would likely be associated
with exposure to the low ambient CO concentrations assessed in some of
the epidemiological studies would be smaller than changes associated
with ``substantially reduced [oxygen] delivery to tissues,'' that might
plausibly lead to the outcomes observed in those studies, with
additional investigation needed to determine whether there may be
another mechanism of action for CO that contributes to the observed
outcomes at low ambient concentrations (ISA, p. 5-48). Thus, there are
uncertainties associated with the epidemiological evidence that
``complicate the quantitative interpretation of the epidemiologic
findings, particularly regarding the biological plausibility of health
effects occurring at COHb levels resulting from exposures to the
ambient CO concentrations'' assessed in these studies (ISA, p. 2-17).
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\27\ In the case of the only other criteria pollutant for which
the health evidence relies on an internal dose metric--lead--the
epidemiological studies also use that metric. For lead (Pb), in
contrast to CO, the epidemiological evidence is focused on
associations of Pb-related health effects with measurements of Pb in
blood, providing a direct linkage between the pollutant, via the
internal biomarker of dose, and the health effects. Thus, for Pb, as
compared to the case for CO, we have less uncertainty in our
interpretations of the epidemiological studies with regard to the
pollutant responsible for the health effects observed. For other
criteria pollutants, including PM and NO2, air
concentrations are used as the exposure/dose metric in both the
epidemiological studies and the other types of health evidence.
Thus, there is no comparable aspect in the PM or NO2
evidence base.
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With regard to health effects other than cardiovascular outcomes,
in addition to noting the complications cited above with regard to
quantitative interpretation of the epidemiological evidence, we note
that the evidence for these other categories of health effects is
considered limited and only suggestive of a causal relationship with
relevant exposures to CO in ambient air, or inadequate to infer such a
relationship, or it supports the conclusion that such a relationship is
not likely (see section II.A.2.b above). As described in the proposal
sections II.B.2 and II.D.2.a, with regard to categories of health
effects or outcomes for which the evidence is considered suggestive,
evidence is lacking that might lend biological plausibility to
epidemiological study results, and also sufficiently rule out the role
of chance, bias and confounding in the epidemiological associations
observed, for outcomes such as developmental or respiratory (ISA,
chapters 1 and 2).
Thus, EPA disagrees with the commenters' conclusion that the
epidemiological evidence establishes that a range of health effects,
including developmental or respiratory effects, are occurring as a
result of exposures to CO in ambient air at or below the current
standards. We additionally disagree with commenters' statements that
imply EPA has inadequately considered the evidence with regard to
protection of sensitive populations and to the protection provided by
the CO standards. As noted in section II.A.2.b above, EPA's assessment
of the current evidence presented in the Integrated Science Assessment
concludes that ``the most important susceptibility characteristic for
increased risk due to CO exposure is [CAD or CHD]'' (ISA, p. 2-10).
Accordingly, the proposal recognized people with cardiovascular disease
as a key population at risk from short-term ambient CO exposures
(proposal, section II.D.4). However, based on assessment of the
evidence in the ISA, the proposal and other documents in this review
also recognize the potential for susceptibility for several other
populations and lifestages, including people with pre-existing diseases
that may already have limited oxygen availability to tissues, increased
COHb levels or increased endogenous CO production, older adults, and
fetuses during critical phases of development (as summarized in section
II.A.2.b above). For these groups and lifestages, the evidence is
incomplete with regard to specific CO exposures or COHb levels that may
be associated with health effects in these groups and the nature of
those effects, as well as a way to relate the specific evidence
available for the CAD population to the limited evidence for these
other populations. Further, the currently available evidence does not
indicate a greater susceptibility for any of the other populations or
lifestages recognized as potentially at risk from exposure to ambient
CO. In reaching a decision on the adequacy of the current standards in
protecting public health in section II.B.3 below, however, the
Administrator has considered EPA's conclusions with regard to the
effects likely to be causally associated with exposure to ambient CO
and population groups particularly at risk, as well as those regarding
the evidence with regard to the potential for other effects and
sensitive groups, and the associated uncertainty. In so doing, as
indicated below, the Administrator judges the current standards to
provide the requisite protection for public health, including the
health of sensitive populations, with an adequate margin of safety.
3. Conclusions Concerning Adequacy of the Primary Standards
Having carefully considered the public comments, as discussed
above, the Administrator believes that the fundamental scientific
conclusions on the effects of CO in ambient air reached in the
Integrated Science Assessment and Policy Assessment, summarized in
sections II.B and II.D of the proposal remain valid. Additionally, the
Administrator believes the judgments she reached in the proposal
(section II.D.4) with regard to consideration of the evidence and
quantitative exposure/dose assessments and advice from CASAC remain
appropriate. Thus, as described below, the Administrator concludes that
the current primary standards provide the requisite protection of
public health with an adequate margin of safety and should be
retained.\28\
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\28\ As explained below in section IV.A, EPA is repromulgating
the Federal Reference Method (FRM) for CO, as set forth in Appendix
C of 40 CFR part 50. Consistent with EPA's decision to retain the
standards, the recodification clarifies and updates the text of the
FRM, but does not make substantive changes to it.
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In considering the adequacy of the current suite of primary CO
standards, the Administrator has carefully considered the available
evidence and conclusions contained in the Integrated Science
Assessment; the information, exposure/dose assessment, rationale and
conclusions presented in the Policy
[[Page 54307]]
Assessment; the advice and recommendations from CASAC; and public
comments. The Administrator places primary consideration on the
evidence obtained from controlled human exposure studies that
demonstrates a reduction in time to onset of exercise-induced markers
of myocardial ischemia in response to increased COHb resulting from
short-term CO exposures, and recognizes the greater significance
accorded both to larger reductions in time to myocardial ischemia and
to more frequent occurrences of myocardial ischemia. As at the time of
the review completed in 1994, the Administrator also takes note of the
results for the modeling of exposures to ambient CO under conditions
simulated to just meet the current, controlling, 8-hour standard in two
study areas, as described in the REA and Policy Assessment, and the
public health significance of those results. She also considers the
newly available and much-expanded epidemiological evidence, including
the complexity associated with quantitative interpretation of these
studies, particularly the few studies available in areas where the
current standards are met. In so doing, she notes that in considering
the adequacy of the current standards, it is important to consider both
the extent to which the evidence supports a causal relationship between
ambient CO exposures and adverse health effects, as well as the extent
to which there is evidence pertinent to such effects under air quality
conditions in which the current standards are met. Further, the
Administrator considers the advice of CASAC, including both their
overall agreement with the Policy Assessment conclusion that the
current evidence and quantitative exposure and dose estimates provide
support for retaining the current standards, as well as their view that
in light of the epidemiological studies, revisions to lower the
standards should be considered and their preference for a lower
standard.
As an initial matter, the Administrator places weight on the long-
standing evidence base that has established key aspects of CO toxicity
that are relevant to this review as they were to the review completed
in 1994. These aspects include the key role played by hypoxia (reduced
oxygen availability) induced by increased COHb blood levels, the
identification of people with cardiovascular disease as a key
population at risk from short-term ambient CO exposures, and the use of
COHb as the bioindicator and dose metric for evaluating CO exposure and
the potential for health effects. The Administrator also recognizes the
Integrated Science Assessment's conclusion that a causal relationship
is likely to exist between relevant short-term exposures to CO and
cardiovascular morbidity.
In placing weight on the controlled human exposure studies, the
Administrator also recognizes the uncertain health significance
associated with the smaller responses to the lowest COHb level assessed
in the study given primary consideration in this review (Allred et al.,
1989a, 1989b, 1991) and with single occurrences of such responses. In
the study by Allred et al. (1989a, 1989b, 1991), a 4-5% reduction in
time (approximately 30 seconds) to the onset of exercise-induced
markers of myocardial ischemia was associated with the 2% COHb level
induced by 1-hour CO exposure. In considering the significance of the
magnitude of the time decrement to onset of myocardial ischemia
observed at the 2% COHb level induced by short-term CO exposure, as
well as the potential for myocardial ischemia to lead to more adverse
outcomes, the EPA generally places less weight on the health
significance associated with infrequent or rare occurrences of COHb
levels at or just above 2% as compared to that associated with repeated
occurrences and occurrences of appreciably higher COHb levels in
response to short-term CO exposures. For example, at the 4% COHb level,
the study by Allred et al., (1989a, 1989b, 1991) observed a 7-12%
reduction in time to the onset of exercise-induced markers of
myocardial ischemia. The Administrator places more weight on this
greater reduction in time to onset of exercise-induced markers compared
to the reduction in time to onset at 2% COHb. The Administrator also
notes that at the time of the 1994 review, an intermediate level of
approximately 3% COHb was identified as a level at which adverse
effects had been demonstrated in persons with angina. Now, as at the
time of the 1994 review, the Administrator primarily considers the 2%
COHb level, resulting from 1-hour CO exposure, in the context of a
margin of safety against effects of concern that have been associated
with higher COHb levels, such as 3-4% COHb.
The Administrator additionally takes note of the now much-expanded
evidence base of epidemiological studies, including the multiple
studies that observe positive associations between cardiovascular
outcomes and short-term ambient CO concentrations across a range of CO
concentrations, including conditions above as well as below the current
NAAQS. She notes particularly the Integrated Science Assessment
conclusion that the findings of CO-associated cardiovascular effects in
these studies are logically coherent with the larger, long-standing
health effects evidence base for CO and the conclusions drawn from it
regarding cardiovascular disease-related susceptibility. In further
considering the epidemiological evidence base with regard to the extent
to which it provides support for conclusions regarding adequacy of the
current standards, the Administrator takes note of CASAC's conclusions
that ``[i]f the epidemiological evidence is given additional weight,
the conclusion could be drawn that health effects are occurring at
levels below the current standard, which would support the tightening
of the current standard'' (Brain and Samet, 2010c). Additionally, the
Administrator places weight on the final Policy Assessment
consideration of aspects that complicate quantitative interpretation of
the epidemiological studies with regard to ambient concentrations that
might be eliciting the reported health outcomes.
For purposes of evaluating the adequacy of the current standards,
the Administrator takes note of the multiple complicating features of
the epidemiological evidence base, as described in more detail in the
final Policy Assessment and in section II.D.2.a of the proposal. First,
while a number of studies observed positive associations of
cardiovascular disease-related outcomes with short-term CO
concentrations, very few of these studies were conducted in areas that
met the current standards throughout the period of study. Additionally,
in CASAC's advice regarding interpretation of the currently available
evidence, they stated that ``[t]he problem of co-pollutants serving as
potential confounders is particularly problematic for CO'' and that
given the currently low ambient CO levels, there is a possibility that
CO is acting as a surrogate for a mix of pollutants generated by fossil
fuel combustion. The CASAC further stated that ``[a] better
understanding of the possible role of co-pollutants is relevant to
regulation'' (Brain and Samet, 2010d). As described in the Policy
Assessment and summarized in section II.B.2 above, there are also
uncertainties related to representation of ambient CO exposures given
the steep concentration gradient near roadways, as well as the
prevalence of measurements below the MDL across the database. The CASAC
additionally indicated the need to consider the potential for
confounding effects of
[[Page 54308]]
indoor sources of CO (Brain and Samet, 2010c). As discussed in section
II.D.2.a of the proposal, the interpretation of epidemiological studies
for CO is further complicated because, in contrast to the situation for
all other criteria pollutants, the epidemiological studies for CO use
an exposure/dose metric (air concentration) that differs from the
metric commonly used in the other key CO health studies (COHb).
The Administrator notes that although CASAC expressed a preference
for a lower standard, CASAC also indicated that the current evidence
provides support for retaining the current suite of standards. CASAC's
recommendations appear to recognize that their preference for a lower
standard was contingent on a judgment as to the weight to be placed on
the epidemiological evidence. Further, as noted above and summarized in
section II.C.2, CASAC has provided a range of advice regarding
interpretation of the CO epidemiological studies in light of the
associated uncertainties. Accordingly, in consideration of the current
evidence with regard to conclusions to be drawn as to the adequacy of
the current standards, the Administrator gives consideration to the
full breadth of CASAC's advice.
In considering the evidence and quantitative exposure and dose
estimates available in this review with regard to the adequacy of
public health protection provided by the current primary standards, the
Administrator recognizes that, as noted in section II.B. above, the
final decision on such judgments is largely a public health policy
judgment, which draws upon scientific information and analyses about
health effects and risks, as well as judgments about how to consider
the range and magnitude of uncertainties that are inherent in the
information and analyses. These judgments are informed by the
recognition that the available health effects evidence generally
reflects a continuum, consisting of ambient levels at which scientists
generally agree that health effects are likely to occur, through lower
levels at which the likelihood and magnitude of the response become
increasingly uncertain. Accordingly, the final decision requires
judgment based on an interpretation of the evidence and other
information that neither overstates nor understates the strength and
limitations of the evidence and information nor the appropriate
inferences to be drawn. As described in section I.A above, the Act does
not require that primary standards be set at a zero-risk level; the
NAAQS must be sufficient but not more stringent than necessary to
protect public health, including the health of sensitive groups, with
an adequate margin of safety.
In considering the judgments to be made regarding adequacy of the
level of protection provided by the current standards, the
Administrator takes particular note of the findings of the exposure and
dose assessment in light of considerations discussed above regarding
the weight given to different COHb levels and their frequency of
occurrence. As described in the proposal, the exposure and dose
assessment results indicate that only a very small percentage of the
at-risk population is estimated to experience a single occurrence in a
year of daily maximum COHb at or above 3.0% COHb under conditions just
meeting the current 8-hour standard in the two study areas evaluated,
and no multiple occurrences are estimated. The Administrator also notes
the results indicating that only a small percentage of the at-risk
populations are estimated to experience a single occurrence of 2% COHb
in a year under conditions just meeting the standard, and still fewer
are estimated to experience multiple such occurrences. Additionally,
consistent with findings of the assessment performed for the review
completed in 1994, less than 0.1% of person-days for the at-risk
populations were estimated to include occurrences of COHb at or above
2% COHb. Taken together, the Administrator judges the current standard
to provide a very high degree of protection for the COHb levels and
associated health effects of concern, as indicated by the extremely low
estimates of occurrences, and to provide slightly less but a still high
degree of protection for the effects associated with lower COHb levels,
the physiological significance of which is less clear.
In further considering the adequacy of the margin of safety
provided by the current standards, the Administrator has additionally
considered conclusions drawn in the Integrated Science Assessment and
Policy Assessment with regard to interpretation of the limited and less
certain information concerning a relationship between exposure to
relevant levels of ambient CO and health effects in other, potentially,
susceptible groups, and with regard to the uncertainties concerning
quantitative interpretation of the available epidemiological studies.
In so doing, the Administrator additionally judges the current
standards to provide adequate protection against the risk of other
health effects for which the evidence is less certain. Further, the
Administrator concludes that consideration of the epidemiological
studies does not lead her to identify a need for any greater
protection. For these and all of the reasons discussed above, and
recognizing the CASAC conclusion that, overall, the current evidence
and REA results provide support for retaining the current standards,
the Administrator concludes that the current suite of primary CO
standards is requisite to protect public health with an adequate margin
of safety from effects of ambient CO.
III. Consideration of a Secondary Standard
As noted in section I.A. above, section 109(b) of the Clean Air Act
requires the Administrator to establish secondary standards that, in
the judgment of the Administrator, are requisite to protect the public
welfare from any known or anticipated adverse effects associated with
the presence of the pollutant in the ambient air. In so doing, the
Administrator seeks to establish standards that are neither more nor
less stringent than necessary for this purpose. The Act does not
require that secondary standards be set to eliminate all risk of
adverse welfare effects, but rather at a level requisite to protect
public welfare from those effects that are judged by the Administrator
to be adverse.
This section presents the rationale for the Administrator's final
decision not to set a secondary NAAQS for CO. In considering the
current air quality criteria, evidence of CO-related welfare effects at
or near ambient levels that are unrelated to climate has not been
identified. Accordingly, in considering whether a secondary standard is
requisite to protect the public welfare, the Administrator has
primarily considered conclusions based on the evidence of a role for CO
in effects on climate. Evaluation of this evidence in the Integrated
Science Assessment and staff considerations in the Policy Assessment
highlighted the limitations in this evidence and provided information
indicating that this role for atmospheric CO is predominantly indirect,
through its role in chemical reactions in the atmosphere which result
in increased concentrations of pollutants with direct contributions to
the greenhouse effect or that deplete stratospheric ozone. Given the
evaluation of the evidence, as well as the views of CASAC, the
Administrator concludes that no secondary standard should be set at
this time because, as in the past reviews, having no standard is
requisite to protect public welfare from any known or anticipated
adverse effects from ambient CO exposures.
In this section, we first summarize the evidence currently
available for welfare
[[Page 54309]]
effects to inform decisions in this review in section III.A. Next, the
rationale for the proposed conclusions is summarized in section III.B.
Public comments and CASAC advice regarding consideration of a secondary
standard in this review are summarized in section III.C. Lastly, the
Administrator's final conclusions with regard to a secondary standard
for CO are presented in section III.D.
A. Introduction
In evaluating whether establishment of a secondary standard for CO
is appropriate at this time, we adopted an approach in this review that
builds upon the general approach used in the last review and reflects
the broader body of evidence and information now available.
Consideration of the evidence available in this review focuses on the
following overarching question: Does the currently available scientific
information provide support for considering the establishment of a
secondary standard for CO?
In considering this overarching question, the Policy Assessment
first noted that the extensive literature search performed for the
current review did not identify any evidence of public welfare effects
of CO unrelated to climate at or near ambient levels (ISA, section 1.3
and p. 1-3). However, ambient CO has been associated with welfare
effects related to climate (ISA, section 3.3). Climate-related effects
of CO were considered for the first time in the 2000 AQCD and are given
somewhat greater focus in the current ISA relative to the 2000 AQCD in
reflection of comments from CASAC and increased attention to the role
of CO in climate forcing (Brain and Samet, 2009; ISA, section 3.3).
Based on the current evidence, the ISA concludes that ``a causal
relationship exists between current atmospheric concentrations of CO
and effects on climate'' (ISA, section 2.2). Accordingly, the
discussion in the Policy Assessment (summarized in the proposal)
focuses on climate-related effects of CO in addressing the question
posed above.
The currently available information summarized in the ISA (ISA
section, 3.3) does not alter the current well-established understanding
of the role of urban and regional CO in continental and global-scale
chemistry, as outlined in the 2000 AQCD (PA, section 3.2). CO absorbs
outgoing thermal infrared radiation very weakly; thus, the direct
contribution of CO itself to climate forcing (or greenhouse warming) is
very small (ISA, p. 3-11). Rather, the most significant effects on
climate are indirect, resulting from CO's role as the major atmospheric
sink for hydroxyl radicals. Through this role of CO in global
atmospheric chemistry, CO influences the abundance of chemically
reactive, major greenhouse gases, such as methane and ozone, that
contribute directly to the greenhouse effect and of other gases that
exert their effect on climate through depletion of stratospheric ozone
(ISA, section 3.3 and p. 3-11). There is significant uncertainty
concerning this effect, and it appears to be highly variable, with the
ISA recognizing that climate effects of changes to emissions of a
short-lived pollutant such as CO are very likely dependent on localized
conditions (ISA section 3.3, pp. 3-12, 3-15, 3-16). As noted in the
ISA, however, ``the indirect [global warming potential] values
evaluated and summarized by [the Intergovernmental Panel on Climate
Change] are global and cannot reflect effects of localized emissions or
emissions changes'' (ISA at p. 3-16). Accordingly, the Policy
Assessment stated that, as a result of the spatial and temporal
variation in emissions and concentrations of CO and the localized
chemical interdependencies that cause the indirect climate effects of
CO, it is highly problematic to evaluate the indirect effects of CO on
climate (PA, p. 3-3).
Based upon the information and considerations summarized above, the
Policy Assessment concluded as an initial matter that, with respect to
non-climate welfare effects, including ecological effects and impacts
to vegetation, there is no currently available scientific information
that supports a CO secondary standard (PA, section 3.4). Secondly, with
respect to climate-related effects, the Policy Assessment recognized
the evidence of climate forcing effects associated with CO, most
predominantly through its participation in chemical reactions in the
atmosphere which contribute to increased concentrations of other more
direct acting climate-forcing pollutants (ISA, sections 2.2 and 3.3).
The PA also noted, however, that the available information provides no
basis for estimating how localized changes in the temporal and spatial
patterns of ambient CO likely to occur across the U.S. with (or
without) a secondary standard would affect local, regional, or
nationwide changes in climate. Moreover, more than half of the indirect
forcing effect of CO is attributable to ozone (O3)
formation, and welfare-related effects of O3 are more
appropriately considered in the context of the review of the
O3 NAAQS, rather than in this CO NAAQS review (PA, section
3.4). For these reasons, the Policy Assessment concluded that there is
insufficient information at this time to support the consideration of a
secondary standard based on CO effects on climate processes (PA,
section 3.4).
B. Rationale for Proposed Decision
In considering a secondary standard for CO, the proposed
conclusions presented in the proposal were based on the assessment and
integrative synthesis of the scientific evidence presented in the ISA,
building on the evidence described in the 2000 AQCD, as well as staff
consideration of this evidence in the Policy Assessment and CASAC
advice. As an initial matter, the proposal concluded that the currently
available scientific information with respect to non-climate welfare
effects, including ecological effects and impacts to vegetation, does
not support a CO secondary standard. Secondly, with respect to climate-
related effects, the proposal took note of staff considerations in the
Policy Assessment and concurred with staff conclusions that information
is insufficient at this time to provide support for a CO secondary
standard. Thus, based on consideration of the evidence, staff
considerations in the Policy Assessment, as well as the views of CASAC,
the Administrator proposed to conclude that no secondary standards
should be set at this time because, as in the past reviews, having no
standard is requisite to protect public welfare from any known or
anticipated adverse effects from ambient CO exposures.
C. Comments on Consideration of Secondary Standard
In considering the need for a secondary standard, the Administrator
first notes the advice and recommendations from CASAC based on their
review of two drafts of the Integrated Science Assessment and of the
draft Policy Assessment. With regard to consideration of a secondary
standard for CO, CASAC noted without objection or disagreement the
staff's conclusions that there is insufficient information to support
consideration of a secondary standard at this time (Brain and Samet,
2010c). One public comment generally concerning EPA's proposed decision
on a secondary standard is addressed below. Other more specific public
comments related to consideration of a secondary standard are addressed
in the Response to Comments document.
One comment (joint submission from Center for Biological Diversity
and others) stated that due to the global influence of CO on climate,
EPA must
[[Page 54310]]
establish a secondary NAAQS. The comment provided no information as to
what form, level, or other elements of a secondary standard would be
appropriate in light of the substantial uncertainties and regional
variation in the indirect effects of CO. Rather, the comment asserted
that there is ``a substantial body of knowledge, as reviewed in the
ISA, regarding CO and climate'' and that ``uncertainty does not absolve
the EPA of the obligation to protect public welfare'' (Center for
Biological Diversity comments at p. 9).
As noted by the commenter, the ISA reviewed the body of knowledge
regarding CO and climate. As discussed above, the ISA concluded that CO
has climate-related effects, that the direct effects of CO are weak,
that there are significant uncertainties concerning the indirect
climate effects of CO, and that these effects appear to be highly
variable and dependent on localized conditions. Further, as noted in
the Policy Assessment, the spatial and temporal variation in emissions
and concentrations of CO and the localized chemical interdependencies
that cause the indirect climate effects of CO make it highly
problematic to evaluate the indirect effects of CO on climate. In light
of the fact that the climate effects of CO are not only uncertain but
highly variable and dependent on local conditions (e.g., concentrations
of other pollutants), EPA believes that there is not adequate
information available to conclude that a secondary standard in the
United States is requisite to protect public welfare. The comment
points to the estimated global effects of CO on climate, but nowhere
does the comment provide evidence that EPA's conclusion regarding
adequacy of the available information is in error.
EPA fully appreciates that the NAAQS are often established on the
frontiers of scientific knowledge, and EPA continually assesses
scientific uncertainties in judging what NAAQS are requisite to protect
public health and welfare. EPA is not asserting that the fact that
there are some uncertainties prevents EPA from setting a standard.
Rather, EPA has judged that, in light of both the significant
uncertainties and the evidence of the direct effects being weak and the
indirect effects being highly variable and dependent on local
conditions, particularly in light of CO's short lifetime, it is not
possible to anticipate how any secondary standard that would limit
ambient CO concentrations in the United States would in turn affect
climate and thus any associated welfare effects. As additionally
discussed in section III.D below, EPA has reviewed the available
information and judged the absence of a standard as being requisite to
protect public welfare.
D. Conclusions Concerning a Secondary Standard
The conclusions presented here are based on the assessment and
integrative synthesis of the scientific evidence presented in the ISA,
building on the evidence described in the 2000 AQCD, as well as staff
consideration of this evidence in the Policy Assessment and CASAC
advice, and with consideration of the views of public commenters on the
need for a secondary standard.
In considering whether the currently available scientific
information supports setting a secondary standard for CO, EPA takes
note of the ISA and Policy Assessment consideration of the body of
available evidence (briefly summarized above in section III.A). First,
EPA concludes that the currently available scientific information with
respect to non-climate welfare effects, including ecological effects
and impacts to vegetation, does not support the need for a CO secondary
standard. Secondly, with respect to climate-related effects, the EPA
takes note of the ISA's conclusions that there are significant
uncertainties concerning the indirect climate effects of CO, and that
these effects appear to be highly variable and dependent on localized
conditions as well as staff considerations in the Policy Assessment and
concurs with staff conclusions that information is insufficient at this
time to support the need for a CO secondary standard. More
specifically, as more fully discussed in consideration of public
comments in section III.C above, EPA has judged that, in light of both
the significant uncertainties and the evidence of the direct effects of
CO on climate being weak and the indirect effects being highly variable
and dependent on local conditions, particularly in light of CO's short
lifetime, it is not possible to anticipate how any secondary standard
that would limit ambient CO concentrations in the United States would
affect climate. Consequently, information that might indicate the need
for additional protection from CO environmental effects and on which
basis EPA might identify a secondary standard for the purposes of
protecting against CO effects on climate processes is not available.
Thus, in considering the evidence, staff considerations in the
Policy Assessment summarized here, as well as the views of CASAC and
the public, summarized above, the Administrator concludes that no
secondary standards should be set at this time because, as in the past
reviews, having no standard is requisite to protect public welfare from
any known or anticipated adverse effects from ambient CO exposures.
IV. Amendments to Ambient Monitoring Requirements
The EPA is finalizing changes to ambient air CO monitoring methods
and the ambient monitoring network design requirements to support the
NAAQS for CO discussed above in Section II. Because ambient CO
monitoring data are essential to the implementation of the NAAQS for
CO, EPA is finalizing minimum monitoring requirements for the ambient
CO monitoring network. State, local, and Tribal monitoring agencies
(``monitoring agencies'') collect ambient CO monitoring data in
accordance with the monitoring requirements contained in 40 CFR parts
50, 53, and 58.
A. Monitoring Methods
This section provides background and rationale for the amendments
that EPA proposed to the Federal Reference Method (FRM) for CO and to
the associated performance specifications for automated CO analyzers.
It also discusses the public comments on those proposed amendments and
the few minor changes made to them as they are being promulgated today.
The use of FRMs for the collection of air monitoring data provides
uniform, reproducible measurements of pollutant concentrations in
ambient air. Federal equivalent methods (FEMs) allow for the
introduction of new or alternative technologies for the same purpose,
provided these methods produce measurements directly comparable to the
reference methods. EPA has established procedures for determining and
designating FRMs and FEMs at 40 CFR part 53.
For ambient air monitoring data for CO to be used for determining
compliance with the CO NAAQS, such data must be obtained using either
an FRM or an FEM, as defined in 40 CFR parts 50 and 53. All CO
monitoring methods in use currently by state and local monitoring
agencies are EPA-designated FRM analyzers. No FEM analyzer, i.e. one
using an alternative measurement principle, has yet been designated by
EPA for CO. These continuous FRM analyzers have been used in monitoring
networks for many years and provide CO monitoring data adequate for
determining CO NAAQS compliance. The current list of all approved FRMs
capable of providing ambient CO data for this purpose may be found on
the EPA Web site, http://www.epa.gov/ttn/amtic/files/ambient/
[[Page 54311]]
criteria/reference-equivalent-methods-list.pdf. Although both the
existing CO FRM in 40 CFR part 50 and the FRM and FEM designation
requirements in part 53 remain adequate to support the CO NAAQS, EPA
nevertheless proposed editorial revisions to the CO FRM and both
technical and editorial revisions to part 53, as discussed below.
1. Proposed Changes to Parts 50 and 53
Reference methods for criteria pollutants are described in several
appendices to 40 CFR part 50; the CO FRM is set forth in appendix C. A
non-dispersive infrared photometry (NDIR) measurement principle is
formally prescribed as the basis for the CO FRM. Appendix C describes
the technical nature of the NDIR measurement principle stipulated for
CO FRM analyzers as well as two acceptable calibration procedures for
CO FRM analyzers. It further requires that an FRM analyzer must meet
specific performance, performance testing, and other requirements set
forth in 40 CFR part 53.
The CO FRM was first promulgated on April 30, 1971 (36 FR 8186), in
conjunction with EPA's establishment (originally as 42 CFR part 410) of
the first NAAQS for six pollutants (including CO) as now set forth in
40 CFR part 50. The method was amended in 1982 and 1983 (47 FR 54922;
48 FR 17355) to incorporate minor updates, but no substantive changes
in the fundamental NDIR measurement technique have been made since its
original promulgation.
In connection with the current review of the NAAQS for CO, EPA
reviewed the existing CO FRM to determine if it was still adequate or
if improved or more suitable measurement technology has become
available to better meet current FRM needs as well as potential future
FRM requirements. EPA determined that no new ambient CO measurement
technique has become available that is superior to the NDIR technique
specified for the current FRM, and that the existing FRM continues to
be well suited for both FRM purposes and for use in routine CO
monitoring. No substantive changes were needed to the basic NDIR FRM
measurement principle. Several high quality FRM analyzer models have
been available for many years and continue to be offered and supported
by multiple analyzer manufacturers.
However, EPA found that the existing CO FRM should be improved and
updated to clarify the language of some provisions, to make the format
match more closely the format of more recently promulgated automated
FRMs, and to better reflect the design and improved performance of
current, commercially available CO FRM analyzers. Accordingly, EPA
proposed appropriate, albeit minor, changes to the FRM. Because these
mostly editorial changes were quite numerous, the entire text of the CO
FRM was revised and re-proposed.
In close association with the proposed editorial revision to the CO
FRM described above, EPA also proposed to update the performance
requirements for CO FRM analyzers that are contained in 40 CFR part 53.
These requirements were established in the 1970's, based primarily on
the NDIR CO measurement technology available at that time. While the
fundamental NDIR measurement principle, as implemented in commercial
FRM analyzers, has changed little over several decades, FRM analyzer
performance has improved markedly. Contemporary advances in digital
electronics, sensor technology, and manufacturing capabilities have
permitted today's NDIR analyzers to exhibit substantially improved
measurement performance, reliability, and operational convenience at
modest cost. This improved instrument performance was not reflected in
the previous performance requirements for CO FRM analyzers specified in
40 CFR part 53, indicating a need for an update to reflect that
improved performance.
The updated performance requirements that EPA proposed for CO
analyzers make them more consistent with the typical performance
capability available in contemporary FRM analyzers and will ensure that
newly designated FRM analyzers will have this improved measurement
performance. A review of analyzer manufacturers' specifications has
determined that all existing CO analyzer models currently in use in the
monitoring network already meet the proposed new requirements (for the
standard measurement range). Also in conjunction with this
modernization of the analyzer performance requirements, EPA proposed
new, more stringent performance requirements applicable, on an optional
basis, to analyzers that feature one or more lower, more sensitive
measurement ranges. Such lower ranges will support improved monitoring
data quality in areas of low CO concentrations.
These updated and new performance requirements are being
promulgated as amendments to subpart B of 40 CFR part 53, which
prescribes the explicit procedures to be used for testing specified
performance aspects of candidate FRM and FEM analyzers, along with the
minimum performance requirements that such analyzers must meet to
qualify for FRM or FEM designation. In particular, the new performance
requirements appear in table B-1 of subpart B of 40 CFR part 53.
Although table B-1 covers candidate methods for sulfur dioxide
(SO2), O3, CO, and NO2, the updates to
table B-1 that EPA is promulgating today affect only candidate methods
for CO.
The updated performance requirements apply to candidate CO
analyzers that operate on the specified ``standard'' measurement range
(0 to 50 ppm). This measurement range remains unchanged from the
existing requirements as it appropriately addresses the monitoring data
needed for assessing attainment. The measurement noise limit is reduced
from 0.5 to 0.2 ppm, and the lower detectable limit is reduced from 1
to 0.4 ppm. Limits for zero drift and span drift are lowered,
respectively, from 1.0 to 0.5 ppm, and from 2.5% to 2.0%. The
previously existing mid-span drift limit requirement, tested at 20% of
the upper range limit (URL), is withdrawn, as EPA has found that the
mid-span drift requirement was unnecessary for CO instruments because
the upper level span drift (tested at 80% of the URL) completely and
more accurately measures analyzer span drift performance.
The lag time limit is reduced from 10 to 2 minutes, and the rise
and fall time limits are lowered from 5 to 2 minutes. For precision,
EPA is changing the form of the precision limit specifications from an
absolute measure (ppm) to percent (of the URL) for CO analyzers and
setting the precision limit at 1 percent tested at both 20% and 80% of
the URL. One percent is equivalent to the previous limit value of 0.5
ppm for precision for the standard (0 to 50 ppm) measurement range.
This change in units from ppm to percent makes the requirement
responsive to higher and lower measurement ranges (i.e., more demanding
for lower ranges).
The interference equivalent limit of 1 ppm for each interferent is
not changed, but EPA is withdrawing the previously existing limit
requirement for the total of all interferents. EPA has found that the
total interferent limit is unnecessary because modern CO analyzers are
subject to only a few interferences, and they tend to be well
controlled.
The new performance requirements apply only to newly designated CO
FRM or FEM analyzers; however, essentially all existing FRM analyzers
in use today, as noted previously, already meet these requirements, so
existing FRM analyzers are not required to be re-tested and re-
[[Page 54312]]
designated under the new requirements. All currently designated FRM
analyzers retain their original FRM designations.
EPA also recognized that some CO monitoring objectives (e.g., area-
wide monitoring away from major roads and rural area surveillance)
require analyzers with lower, more sensitive measurement ranges than
the standard range used for typical ambient monitoring. To improve data
quality for such lower-range measurements, EPA is adding a separate set
of performance requirements that apply specifically to lower ranges
(i.e., those having a URL of less than 50 ppm) for CO analyzers. These
additional, lower-range requirements are listed in the revised table B-
1. A candidate analyzer that meets the table B-1 requirements for the
standard measurement range (0 to 50 ppm) can optionally have one or
more lower ranges included in its FRM or FEM designation by further
testing to show that it also meets these supplemental, lower-range
requirements.
Although no substantive changes were determined to be needed to the
test procedures and associated provisions of subpart B for CO, the
detailed language in many of the subpart B sections was in need of
significant updates, clarifications, refinement, and (in a few cases)
correction of minor typographical errors. These changes to the subpart
B text (apart from the changes proposed for table B-1 discussed above)
are very minor and almost entirely editorial in nature, but quite
numerous. Therefore, EPA has revised and is re-promulgating the entire
text of subpart B text.
As discussed previously, table B-1, which sets forth the pollutant-
specific performance limits, is being amended only as applicable to CO
analyzers. EPA amended table B-1 as applicable to SO2
methods on June 22, 2010 and intends to amend table B-1 for
O3 and NO2 later, if appropriate, when the
associated NAAQS are reviewed.
2. Public Comments
EPA notes first that CASAC stated that ``more sensitive and precise
monitors need to be deployed to measure levels that are less than or
equal to 1 ppm.'' (Brain and Samet 2010b). Comments from the public on
the proposed revisions to CO monitoring methods are addressed in this
section or in the Response to Comments document. Comments on the
proposed changes to the CO monitoring methodology were received from
only one member of the public, the American Petroleum Institute. The
commenter was generally supportive of EPA's efforts to clarify and
update the regulations for the CO FRM and the CO analyzer performance
requirements. In regard to the CO FRM (40 CFR part 50, appendix C), the
commenter questioned EPA's proposed relaxation in a flow rate control
requirement in the dilution-method calibration procedure, from 1% to
2%. However, EPA believes that the original 1% requirement is
unnecessarily stringent, and that this change is appropriate and
commensurate with the existing 2% flow rate measurement accuracy and
with the overall calibration accuracy needed to obtain adequate data
quality with the method.
To further improve clarity of the FRM calibration section, the
commenter also suggested a minor change to Equation 1 and the addition
of language indicating that the measurement display or read-out device
connected to the analyzer to monitor its reading during calibration
should be the actual, or at least closely representative of the actual,
data recording system used during field operation of the analyzer. EPA
has accepted both of these suggestions, and appropriate changes have
been incorporated into the changes being made to the CO FRM in this
action.
Another comment questioned the proposed withdrawal of the previous
total interference limit requirement. In response to this comment, EPA
re-evaluated the efficacy of this limit for CO analyzers and again
determined that the limit was not necessary, because the number of
individual interferences to which FRM (and most potential FEM) CO
analyzers are subject is small (only 2 for FRMs), as listed in table B-
3 of 40 CFR part 53. Also, response to these interferents is typically
well controlled in modern CO analyzers. In addition, the new,
individual interference limit for the lower measurement ranges is one
half the limit for the standard range, which further mitigates any need
for a separate, total interference limit.
The commenter questioned EPA's proposed withdrawal of the
previously existing limit requirement for span drift measured at 20% of
the upper range limit (URL), contending that this limit was important
because it is closer in concentration to the existing NAAQS than the
span drift measured at 80% of the URL. However, the purpose of the span
drift limit is not to directly assess measurement error at a
particular, mid-scale concentration level. That purpose is served by
the 1-point quality control check for CO monitors described in section
3.2.1 of appendix A of 40 CFR part 58. Rather, for the purpose of
analyzer performance testing, the linear input/output functional
characteristic of the analyzer is best described by its zero point and
its slope, because these parameters are generally subject to change
(drift) independently. Thus, zero drift (change in the zero point) and
span drift (change in the slope) are tested separately. Zero drift is,
of course, measured at zero concentration, and span drift is most
accurately measured at a concentration near the URL. The span drift
test at 80% URL (when the zero drift is within the specified
requirement) more accurately determines any change in the slope
parameter then a test at 20% URL. The previously specified test at 20%
URL thus serves little, if any, purpose in regard to determining change
in the slope. Therefore, EPA has concluded that this requirement can be
withdrawn.
Finally, the commenter was concerned that existing FRM analyzers
approved under the previously existing performance requirements may
provide data quality inferior to that of analyzers approved under the
proposed new requirements and that older analyzers may be unacceptable
for some applications that demanded higher performance or higher data
quality. A ``tiered'' approach was suggested to handle this situation.
In proposing more stringent performance requirements for approval
of new FRM and FEM analyzers, EPA noted that the performance of
analyzers approved under the existing performance requirements was
fully adequate for most routine compliance monitoring applications, and
that the proposed new requirements were largely to bring the base FRM
and FEM performance requirements up to date and more commensurate with
the performance of modern commercially available CO analyzers. EPA
further noted that all currently designated FRM analyzers already meet
the proposed new requirements. This means that the quality of routine
CO monitoring data currently being obtained is already of the higher
level portended by the proposed new performance requirements.
In the proposal, however, EPA did recognize that some special CO
monitoring applications do require a higher level of performance than
that required for routine applications. Therefore, EPA is promulgating
optional, more stringent performance requirements for analyzers having
a more sensitive, ``lower range'' available for such applications. This
is, in fact, a ``tiered'' approach. Applicants would be able to elect
to have such lower ranges approved as part of their FRM or FEM
designation. These new, special performance requirements will alert
monitoring agencies that they should
[[Page 54313]]
consider low-range performance of an analyzer for those applications
that may require better low-level performance, and they can select an
analyzer that has such a lower range approved under its FRM (or FEM)
designation.
3. Decisions on Methods
As discussed above, a few relatively minor changes have been
incorporated into the proposed revised CO FRM in appendix C of part 50,
in response to public comments received by EPA. With these changes, the
revised appendix C is being promulgated as otherwise proposed. Only one
change has been made to the revision proposed for subpart B of part 53,
to fix a typographical error that appeared in proposed table B-1
concerning reversed entries for the span drift limits for the 20% and
80% URL for the CO ``lower range'' column. Aside from this correction,
the revised subpart B is being promulgated exactly as proposed.
B. Network Design
This section on CO network design provides information on the
proposed network design, the public comments received on the proposed
network design, and the EPA's conclusions, including rationale and
details, on the final changes to the CO network design requirements.
1. Proposed Changes
The objective of an ambient monitoring network is to (1) provide
air pollution data to the general public in a timely manner, (2)
support compliance with ambient air quality standards and emissions
strategy development, and (3) provide support for air pollution
research (40 CFR part 58, appendix D). The proposed CO network design
was intended to directly support the NAAQS by requiring monitoring that
provides data for use in the designation process and ongoing assessment
of air quality. In particular, the proposed network design was intended
to require a sufficient number of monitors to collect data for
compliance purposes in the near-road environment, where, as noted in
section II.A.1 above, the highest ambient CO concentrations generally
occur, particularly in urban areas (ISA, section 3.5.1.3; REA, section
3.1.3).
The EPA proposed CO monitors to be required within a subset of
near-road NO2 monitoring stations, which are required in 40
CFR part 58, appendix D, section 4.3. Per the preamble to the final
rule for the NO2 NAAQS promulgated on February 9th, 2010 (75
FR 6474), near-road NO2 monitoring stations are intended to
be placed in the near-road environment at locations of expected maximum
1-hour NO2 concentrations and are triggered for metropolitan
areas based on Core Based Statistical Area (CBSA) population thresholds
and a traffic-related threshold based on annual average daily traffic
(AADT).\29\ The EPA proposed that CO monitors be required to operate in
any CBSA having a population of 1 million or more persons, collocated
with required near-road NO2 monitoring stations. Based upon
2009 Census Bureau estimates and 2008 traffic statistics maintained by
the US Department of Transportation (US DOT) Federal Highways
Administration (FHWA), the CO monitoring proposal was estimated to
require approximately 77 CO monitors to be collocated with near-road
NO2 monitors within 53 CBSAs.\30\
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\29\ One near-road NO2 monitor is required in any
CBSA having a population of 500,000 or more persons. Two near-road
NO2 monitors are required in any CBSA having a population
of 2.5 million or more persons, or in any CBSA that has one or more
road segments with an AADT count of 250,000 or more (40 CFR part 58,
appendix D, section 4.3).
\30\ Since the proposal, EPA has estimated that using 2010
Census Bureau counts the proposed rule would have resulted in
approximately 75 monitors in 52 CBSAs being required.
---------------------------------------------------------------------------
The EPA proposed that any required near-road CO monitors shall be
reflected in State annual monitoring network plans due in July 2012.
Further, the Agency proposed that required near-road CO monitors be
operational by January 1, 2013. Due to the proposed collocation of
required CO monitors with required near-road NO2 monitors,
these implementation dates were proposed in order to match those of the
forthcoming near-road NO2 monitoring network.
In light of the proposal to require near-road CO monitors be
collocated with required near-road NO2 monitors, the EPA
proposed that siting criteria for microscale CO monitors be revised to
match those of microscale near-road NO2 monitors (and also
microscale PM2.5 monitors). In particular, the EPA proposed
that microscale CO siting criteria for probe height and horizontal
spacing be changed to match those of near-road NO2 monitors
as prescribed in 40 CFR part 58 appendix E, sections 2, 4(d), 6.4(a),
and table E-4. Specifically, EPA proposed the following: (1) To allow
microscale CO monitor inlet probes to be between 2 and 7 meters above
the ground; (2) that microscale near-road CO monitor inlet probes be
placed so they have an unobstructed air flow, where no obstacles exist
at or above the height of the monitor probe, between the monitor probe
and the outside nearest edge of the traffic lanes of the target road
segment; and (3) that required near-road CO monitor inlet probes shall
be as near as practicable to the outside nearest edge of the traffic
lanes of the target road segment, but shall not be located at a
distance greater than 50 meters in the horizontal from the outside
nearest edge of the traffic lanes of the target road segment.
Finally, the EPA recognized that a single monitoring network design
may not always be sufficient for fulfilling specific or otherwise
unique data needs or monitoring objectives for every area across the
nation. As such, the EPA proposed to provide the Regional
Administrators with the discretion to require monitoring above the
minimum requirements as necessary to address situations where minimum
monitoring requirements are not sufficient to meet monitoring
objectives.
2. Public Comments
EPA first notes that CASAC expressed concern over the current
monitoring network, stating ``[m]ore extensive coverage may be
warranted for areas where concentrations may be more elevated, such as
near roadway locations. The Panel found that in some instances current
networks underestimated carbon monoxide levels near roadways.'' (Brain
and Samet 2010b). General comments from the public based on relevant
factors that either support or oppose the proposed changes to the CO
network design are addressed in this section. Specific public comments
related to the network design, but with regard to material which was
not specifically proposed by the EPA or posed for solicitation of
comment, are addressed in the Response to Comments document.
a. Near-Road Monitoring and Collocation With Near-Road Nitrogen Dioxide
Monitors
The EPA received multiple public comments on the overall merit of
monitoring for CO in the near-road environment, the proposal that
required CO monitors be collocated with required near-road
NO2 monitors, and the number of required CO monitors that
might be appropriate. In general, public health and environmental
groups (e.g., American Lung Association [ALA], American Thoracic
Society [ATS], Environmental Defense Fund [EDF]), some states or state
environmental agencies or organizations (e.g. National Association of
Clean Air Agencies [NACAA], Northeast States for Coordinated Air Use
Management [NESCAUM], New York State Department of Environment
Conservation [NYSDEC], and State of Wisconsin Department of Natural
[[Page 54314]]
Resources [WIDNR]), and some private citizen commenters provided
support for a requirement for CO monitors in the near-road environment.
For example, ALA, ATS, and EDF state that they ``* * * are pleased to
see EPA take seriously the public health threats that are posed to
millions of residents and other sensitive receptors who live near or
work on or near highways as well as other high exposure areas.'' They
go on to note that ``[near-road ambient monitoring] data have been
sorely lacking from the national monitoring network and are long
overdue.'' Further, many of the commenters who were supportive of near-
road monitoring were supportive of collocating CO monitors with near-
road NO2 monitors as it establishes multipollutant
monitoring within the ambient air monitoring network. For example,
NACAA stated the following in their comments: ``* * * NACAA supports
EPA's proposal to collocate CO near roadway monitors at a subset of
NO2 near-roadway sites. This is consistent with the
recommendations of EPA's Clean Air Scientific Advisory Committee
(CASAC), which urged the agency to develop the near roadway monitoring
network with a multipollutant focus and included CO in its list of
pollutants that should be measured.''
Some industry commenters (e.g., Association of Automobile
Manufacturers [AAM] and American Electric Power Service Corporation
[AEPSC]) and a number of other states or state groups (e.g., Indiana
Department of Environmental Management [IDEM], North Carolina
Department of Air Quality [NCDAQ], New Mexico Air Quality Bureau
[NMAQB], South Carolina Department of Health and Environmental Control
[SCDHEC], Southeast Michigan Council of Governments [SEMCOG], and Texas
Commission on Environmental Quality [TCEQ]) generally did not support
the proposed near-road CO monitoring requirements. For example, IDEM
stated that ``CO measured by roadside monitors is not representative of
ambient air quality everywhere in a city or county containing the
roadway'' and that ``* * * roadside monitoring measurements represent
source-specific data. Therefore, Indiana does not believe that roadside
monitoring should apply to an ambient air quality standard.'' SCDHEC
stated it ``* * * does not believe that the use of a near-road
monitoring network in a state-wide ambient air monitoring network is
the appropriate choice to protect our community's public health'' and
that ``this monitoring method biases the monitoring effort into areas
of little or no population while monitoring for the community
population exposure is neglected.'' Similarly, industry commenter AAM
stated that ``the current proposal does not include a requirement that
the near-roadway monitors be sited in locations where there is actual
human exposure to the ambient air for time periods corresponding to the
1-hour or 8-hour CO NAAQS.''
The EPA stated in the CO proposal (76 FR 8158) that the proposed
near-road CO monitoring requirements were intended to ensure a network
of adequate size and focus to provide data for comparison to the NAAQS,
support health studies and model verification, and to fulfill Agency
multipollutant monitoring objectives. In response to the comment that
near-road monitoring data would be ``source-specific'' and may not be
appropriately applicable to an ambient air standard, the Agency notes
that monitoring for CO in the near-road environment (as a mobile source
oriented measurement) is a longstanding agency practice, as evidenced
by the first monitoring rule promulgated in 1979 (44 FR 27558, May 10,
1979). That 1979 monitoring rule included the requirement to monitor
for ``peak'' CO concentrations in urban areas having populations of
500,000 people or more in locations ``* * * around major traffic
arteries and near heavily traveled streets in downtown areas.'' The
Agency believes that the use of near-road CO monitors as proposed is
not a departure from the Agency's longstanding intent to measure peak
concentrations of CO in the near-road environment. Rather, the proposal
was consistent with the Agency's approach to require monitors for CO,
and other criteria pollutants, in locations that likely experience peak
ambient concentrations. The Agency also notes that source-oriented
monitoring is and has long been a common practice in ambient monitoring
networks, although more often associated with stationary sources, where
the ambient data collected are used for comparison to the NAAQS. Data
on ambient air concentrations, including near-road data, which may be
most appropriately classified as on-road mobile source oriented, are
appropriate to compare to the NAAQS.
With regard to the comments asserting that near-road monitoring
would result in monitoring areas of ``little or no population'' and
thus population exposure is not represented, the EPA notes that on-road
mobile sources are ubiquitous in urban areas and are a dominant
component of the national CO emissions inventory, at nearly 60% of the
total inventory, based on the 2008 NEI. As such, microenvironments
influenced by on-road mobile sources are important contributors to
ambient CO exposures, particularly in urban areas (REA, section 2.7).
Further, the ambient CO exposures of most concern are short-term.
Accordingly, near-road monitoring is focused on characterizing peak or
elevated ambient concentrations. The relevance of this focus for the
purposes of both ensuring compliance with the NAAQS and gathering data
to inform our consideration of ambient CO exposures is demonstrated by
the ubiquity of on-road mobile sources throughout urban areas, the time
spent by people on or near roadways and the large number of American
citizens living in urban areas and near roadways. As was noted in the
ISA, the 2007 American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs07/ahs07.html) estimates that 17.9 million housing units
are within 300 feet (~91 meters) of a 4-lane highway, airport, or
railroad. Using the same survey, and considering that the average
number of residential occupants in a housing unit is approximately
2.25, an estimate can be made that at least 40 million American
citizens live near 4-lane highways, airports, or railroads. Among these
three transportation facilities, roads are the most pervasive of the
three, suggesting that a significant number of people may live near
major roads. Furthermore, the 2008 American Time Use Survey (http://www.bls.gov/tus/) reported that the average U.S. civilian spent over 70
minutes traveling per day. Based on these considerations, the Agency
has concluded that monitoring in the near-road environment would
characterize the ambient concentrations that contribute to ambient CO
exposure for a significant portion of the population that would
otherwise not be captured.
The AAM also commented that the EPA ``* * * proposal to locate more
near roadway monitors appears to be an attempt to find problems where
none are likely to exist.'' The Agency proposal for near-road monitors
is in line with longstanding monitoring objectives to monitor for peak
or elevated ambient pollutant concentrations where they may occur. The
Agency agrees that CO is no longer as pervasive a problem as it was in
the past; however, there is still a responsibility to appropriately
characterize and assess ambient concentrations to ensure that they do
not exceed the NAAQS. In comments on the first draft of the ISA, CASAC
advised that ``* * * relying only on
[[Page 54315]]
EPA's [current] fixed monitoring network, CO measurements may
underestimate CO exposures for specific vulnerable populations such as
individuals residing near heavily trafficked roads and who commute to
work on a daily basis.'' In comments on the second draft of the ISA,
CASAC commented that ``the panel expresses concern about the existing
CO monitoring network, both for its [spatial] coverage and for its
utility in estimating human exposure'' and that ``CO exposures may not
be adequately characterized for populations that may be exposed to
higher CO levels because of where they live and work,'' such as the
near-road environment. Finally, in comments on the second draft of the
REA, CASAC stated that ``the approach for siting monitors needs greater
consideration. More extensive coverage may be warranted for areas where
concentrations may be more elevated, such as near-roadway locations.''
In light of these comments and upon a review of the existing CO
network, the Administrator concluded that the current CO monitoring
network (circa 2010) lacked a necessary focus. While some currently
existing sites that were established in the 1970s and 1980s continue to
monitor near-road locations in downtown areas or within urban street
canyons, and a minimum number of area-wide monitors are currently
required at National Core (NCore) multipollutant stations, few monitors
exist that characterize the more heavily trafficked roads that are
prevalent in the modern roadway network, particularly in our larger
urban areas. The Agency's proposal was intended to require a modest but
appropriate number of CO monitors to characterize the near-road
environment where peak or elevated ambient CO concentrations are
expected to occur near heavily trafficked roads, as compared with
neighborhood or urban background concentrations. If CO levels turn out
to be low in these near-road locations, so much the better for public
health, and monitoring networks can be adjusted in the future, as they
have over time in response to an increased understanding of where
levels of concern to public health are likely to occur.
Although the EPA received a number of comments that were largely
supportive for the proposed requirement of collocating CO monitors
within the forthcoming near-road NO2 monitoring stations,
several commenters encouraged the Agency to provide flexibility to
allow for the separation of the newly required CO monitors from the
near-road NO2 sites, if necessary, to better monitor peak
near-road CO concentrations. In their comments supporting the
collocation concept, NACAA also stated that their organization ``* * *
also encourages EPA to allow flexibility for state and local agencies
to use alternative siting of near-roadway CO monitors on a case-by-case
basis, where there is a scientific justification for siting the CO
monitor in a different location from the NO2 monitor, to
ensure the best possible measurement of near roadway CO
concentrations.'' Similarly, NCDAQ recognized that ``* * * light duty
vehicles tend to have more impact on CO concentrations than do heavy
[duty] vehicles'' and went on to surmise that ``* * * not all near-road
NO2 monitoring stations will be well situated to measure
maximum CO concentrations.''
The Agency has expressed its intent to pursue the integration of
monitoring networks and programs through the encouragement of
multipollutant monitoring wherever possible, as evidenced by actions
taken in the 2006 monitoring rule that created the NCore network, the
expression of the multipollutant paradigm in the 2008 Ambient Air
Monitoring Strategy for State, Local, and Tribal Air Agencies, and
within this rulemaking process as part of the rationale in proposing
the collocation of required near-road CO monitors with near-road
NO2 monitors. Multipollutant monitoring is viewed as a means
to broaden the understanding of air quality conditions and pollutant
interactions, furthering the capability to evaluate air quality models,
develop emission control strategies, and support research, including
health studies. However, the Agency also recognizes that the
measurement objectives of individual pollutants may not always
correspond in a way that would support multipollutant monitoring as the
most appropriate option in a network design. On the issue raised by
NACAA and NCDAQ concerning the potential difference in locations of
peak CO and NO2 concentrations in the near-road environment,
the EPA recognizes the primary influence to be the different emission
characteristics between light duty (LD) and heavy duty (HD) vehicles
and vehicle operating conditions, which were discussed in section
III.B.2 of the CO proposal. The public comments suggesting the need for
flexibility in siting near-road CO monitors derives from the fact that
near-road NO2 sites will be sited at locations where peak
NO2 are expected to occur. Since NO2 is more
heavily influenced by HD vehicles and CO is more heavily influenced by
LD vehicles on a per vehicle basis, respectively, there may be cases
where the peak CO and NO2 concentrations could occur along
different road segments within the same CBSA. As a general observation,
the EPA believes that this situation may have more likelihood of
occurring in the relatively larger (by population) CBSAs where a higher
number of heavily trafficked roads with a wider variety of fleet mix
(e.g. HD to LD vehicle ratios) tend to exist versus relatively smaller
CBSAs. In recognition of these considerations, the final regulation
allows for flexibility in CO monitor placement in the near-road
environment when justified, as discussed below in section IV.B.3.
b. Population Thresholds for Requiring Near-Road Carbon Monoxide
Monitors
The EPA proposed that required CO monitors be collocated with every
required near-road NO2 monitor in a CBSA with a population
of 1 million or more persons. Due to the requirement to locate one CO
monitor at each required near-road NO2 site, the proposal
would have required two monitors in each CBSA having 2.5 million or
more persons or having one or more road segments with Annual Average
Daily Traffic (AADT) counts of 250,000 or more. The proposal would have
also required one monitor within those CBSAs having 1 million or more
persons (but fewer than 2.5 million persons).\31\ Based upon 2009
Census Bureau estimates and US DOT maintained traffic summary data, the
proposal was estimated to require 77 monitors within 53 CBSAs. Using
recent 2010 Census data, and US DOT maintained traffic summary data,
the proposal would have required approximately 75 monitors within 52
CBSAs.
---------------------------------------------------------------------------
\31\ One near-road NO2 monitor is required in any
CBSA having a population of 500,000 or more persons. Two near-road
NO2 monitors are required in CBSAs with population of
greater than 2.5 million, or in any CBSA with a population of
500,000 or more persons that has one or more roadway segments with
annual average daily traffic (AADT) counts of 250,000 or more. (40
CFR part 58, Appendix D, Section 4.3).
---------------------------------------------------------------------------
The EPA received a number of comments supporting different
population thresholds by which to require near-road CO monitors. Those
state agencies or state agency groups who generally supported required
CO monitoring in the near-road environment (e.g., NACAA, NESCAUM,
NYSDEC, and WIDNR) suggested a population threshold of 2.5 million by
which near-road CO monitors should be required. In addition, NCDAQ, who
did not support near-road CO monitoring,
[[Page 54316]]
suggested that if it is required, it be required only within CBSAs of
2.5 million or more. The use of a population threshold of 2.5 million
persons, versus 1 million as proposed, would require approximately 42
near-road CO monitors within 21 CBSAs, based on 2010 Census data.
Industry commenter American Petroleum Institute (API) stated that the
proposed population threshold of 1 million persons ``* * * appears
appropriate, but EPA should not require that both [near-road
NO2] sites in the largest CBSAs host CO monitors.'' API's
suggestion would require approximately 52 near-road CO monitors within
52 CBSAs. Finally, the public health and environmental groups ALA, ATS,
and EDF suggested the EPA promulgate minimum monitoring requirements
``* * * to encompass cities in smaller metro areas, including cities
with populations of 500,000 or more, similar to the requirements for
NO2 roadside monitoring.'' ALA, ATS, and EDF's suggestion
would result in the requirement of approximately 126 monitors within
103 CBSAs.
As was noted in the proposal, the Agency believes that with the
continuing decline of ambient CO levels, as summarized in the EPA's
most recent trends report Our Nation's Air: Status and Trends Through
2008 (http://www.epa.gov/airtrends/2010/), there is less likelihood for
high CO concentrations in relatively smaller CBSAs (by population).
Accordingly, the Agency proposed the requirement for what it believed
would be a sufficient number of CO monitors, which would be collocated
with required near-road NO2 monitors in CBSAs having
populations of 1 million or more persons. The Administrator considered
alternative population thresholds, including the 2.5 million and
500,000 person thresholds, but concluded that those thresholds would
require too few or too many monitors, respectively, in light of
existing information on CO emissions data, ambient data, and the lack
of data for locations near highly trafficked roads. The rationale for
the proposed 1 million person threshold was to require a modest but
sufficiently sized network that would effectively assess near-road CO
concentrations for comparison to the NAAQS and could also provide data
from within a multipollutant framework to support research (which
includes health studies), facilitate model verification, and assess and
evaluate emissions control strategies. However, after considering
public comments, the EPA has concluded that one monitor in each CBSA of
1 million or more persons will provide for monitoring of a wide range
of diverse situations with regard to traffic volume, traffic patterns,
roadway designs, terrain/topography, meteorology, climate, as well as
surrounding land use and population characteristics. Accordingly, in
the final rule EPA has modified the proposed requirements for CO
monitors so that only one CO monitor is required in CBSAs of 1 million
or more persons, as discussed in Section IV.B.3 below.
c. Implementation Schedule
The EPA received a number of comments on the timeline for
implementation of any required CO monitoring promulgated as part of
this rulemaking. ALA, ATS, and EDF stated that they ``* * * support
EPA's requirement that CO monitors be installed in near-highway
locations by July 1, 2013.'' In light of the support these commenters
expressed for rapid deployment of near road CO monitors, these
commenters may have intended to support the proposed implementation
date of January 1, 2013 instead of July 1, 2013 as quoted. The Agency
received a number of comments from state agencies, state agency
organizations, and industry encouraging the Agency to extend the time
by which any required monitoring must be implemented. For example, API
suggested that the proposed date by which required near-road CO
monitors be established be extended to July 1, 2013, while NACAA and
WIDNR suggested January 1, 2014. Several commenters suggested that
required near-road monitors should be phased in over a period of time.
For example, NACAA, stated ``[i]t may be necessary to develop a program
for phasing in new monitoring sites and reevaluate network
implementation.'' NACAA also pointed to comments from CASAC that it
would be advisable to phase in near-road monitoring for NO2,
because ``[t]he first round of sites could be used to gather
information on appropriate siting in the near roadway environment, near
roadway gradient, and spatial relationships.''
The EPA recognizes that states are already implementing newly
required monitoring related to lead and NO2, and that the
current financial and logistical burdens may make the implementation of
new monitoring requirements difficult. A number of state and industry
commenters noted the need for funding to accommodate a new monitoring
requirement, and some also noted the financial and logistical hardships
that many states are currently experiencing (e.g., IDEM, NACAA, NCDAQ,
SCDHEC, and WIDNR). The EPA recognizes the significance of the
financial and logistical burden that new monitoring requirements pose
and the impact of multiple new monitoring requirements stemming from
other recent rulemakings. As such, the Agency has taken these comments
into consideration in the final rule with regard to when required CO
monitors are to be operational, as discussed in Section IV.B.3 below.
d. Siting Criteria
The EPA received comments regarding the proposed revisions to
microscale CO siting criteria. Those who commented (AAM, API, and
NCDAQ) all supported having two sets of siting criteria that would
apply to near-road CO monitors such as those that might be collocated
with near-road NO2 monitors and to those CO monitors
operating in downtown areas and urban street canyon locations,
respectively. AAM stated that ``* * * there should be two separate
criteria for siting microscale CO monitors. The earlier height and
distance guidelines are still appropriate for downtown areas and
arterial highways with sidewalks, but a separate set of guidelines
should be established for limited access, heavily-travelled
expressways.'' API commented that ``* * * the proposed CO [near-road]
criteria are acceptable. EPA should create two-tiered siting criteria
for microscale CO monitoring * * *'' and that ``there will be an
ongoing need for CO monitoring in downtown, urban and/or street
canyon[s] for health-related concerns as well as SIP-related issues.''
Finally, NCDAQ stated that ``* * * the US EPA should maintain separate
siting criteria for the two types of micro-scale CO monitoring sites *
* *'' noting that the current siting criteria intended for downtown
areas and urban street canyon sites ``* * * are still valid for that
purpose and CO monitoring stations being placed for this purpose should
still be required to meet these siting criteria.''
The EPA agrees with the commenters that the existing siting
criteria are still appropriate for any existing or future downtown area
or urban street canyon CO monitoring site, and that new siting criteria
are appropriate for CO monitors being collocated with near road
NO2 monitors. As such, the Agency is finalizing siting
criteria for microscale CO sites that include criteria for both
downtown area/urban street canyon microscale sites and other near-road
microscale CO sites, as presented below in Section IV.B.3.
e. Area-Wide Monitoring
The EPA received a number of comments from transportation groups,
[[Page 54317]]
public health and environmental groups, and an industry commenter
(e.g., AAM, ALA/ATS/EDF, American Association of State Highway and
Transportation Officials [AASHTO], New York State Department of
Transportation [NYSDOT], Texas Department of Transportation [TXDOT],
and Virginia Department of Transportation [VDOT]) regarding the fate of
many of the CO monitors in the current network that characterize
concentrations representative of neighborhood or larger spatial
scales,\32\ known as area-wide monitors. For example, AASHTO commented
that ``EPA appears to be proposing that CO monitoring sites to
characterize area-wide CO concentration levels at the neighborhood and
larger spatial scales is no longer required. AASHTO is concerned that
this proposal will de-emphasize the need for neighborhood scale CO
monitors.'' AASHTO and some state DOTs expressed that the data for
neighborhood scale monitors are used for other purposes, such as
National Environmental Policy Act (NEPA) and transportation conformity,
and that they are concerned about the potential loss of these types of
data in the future. In another example, ALA/ATS/EDF stated that they
call upon EPA to ``establish a comprehensive roadside air pollution
network, while retaining the current area-wide CO network.''
---------------------------------------------------------------------------
\32\ Spatial scales are defined in 40 CFR Part 58 Appendix D,
Section 1.2, where the scales of representativeness of most interest
for the monitoring site types include:
1. Microscale--Defines the concentration in air volumes
associated with area dimensions ranging from several meters up to
about 100 meters.
2. Middle scale--Defines the concentration typical of areas up
to several city blocks in size, with dimensions ranging from about
100 meters to 0.5 kilometers.
3. Neighborhood scale--Defines concentrations within some
extended area of the city that has relatively uniform land use with
dimensions in the 0.5 to 4.0 kilometers range.
4. Urban scale--Defines concentrations within an area of city-
like dimensions, on the order of 4 to 50 kilometers. Within a city,
the geographic placement of sources may result in there being no
single site that can be said to represent air quality on an urban
scale. The neighborhood and urban scales have the potential to
overlap in applications that concern secondarily formed or
homogeneously distributed air pollutants.
5. Regional scale--Defines usually a rural area of reasonably
homogeneous geography without large sources, and extends from tens
to hundreds of kilometers.
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The EPA notes that prior to this final rulemaking, the only
required CO monitoring within 40 CFR part 58, appendix D was for the
operation of a CO monitor within all NCore multipollutant monitoring
stations. There are approximately 80 NCore stations nationwide, and by
design, they are area-wide monitoring sites. In the proposal, the
Agency estimated that 345 CO monitors were operational at some point
during 2009. A more recent examination of AQS data (utilizing EPA's Air
Explorer Web tools located at http://www.epa.gov/airexplorer) indicate
that approximately 328 CO monitors were operational as of May 20, 2011.
These 328 active CO monitors include the 80 NCore monitors now in
operation nationwide. This means that a significant portion of the
current network is composed of monitors that are additional to those
required by EPA as part of a national network design. It is critical to
note that in this rulemaking the EPA is actually increasing the total
number of required sites in the national CO monitoring network design
and is not removing any area-wide monitoring requirements as AASHTO and
other commenters suggested. Some of the potential for misperception on
this issue may have arisen from the Agency's stated expectation that
state and local air monitoring agencies will likely move existing CO
monitors into near-road locations to satisfy the minimum monitoring
requirements promulgated in this rulemaking. Based on this final rule,
state and local agencies would only move, at most, approximately 52
monitors out of the 328 in operation (circa May 2011). Therefore a
majority of CO monitors would likely continue operating in their
existing locations. However, it should be noted that with ambient CO
concentrations well below the NAAQS, particularly at area-wide sites,
states may identify some area-wide CO monitors to be no longer
necessary. As such, the retirement of these sites may be justified, and
their removal would save state and local resources. The EPA does
recognize the value of maintaining some level of area-wide CO
monitoring to meet the overarching monitoring objectives, which
includes tracking long-term trends and to support research. In the
proposal, the Agency did not propose establishing requirements for
additional area-wide monitoring sites because: (1) There is the
existing NCore requirement, and (2) there is an expectation based on
experience that some number of non-required area-wide sites will
continue to operate in the future without minimum monitoring
requirements. Regarding the removal or shutdown of any individual
ambient air pollutant monitor, the Agency notes that there is a
publicly transparent process by which any existing CO monitor would be
shut-down. The shut-down of any State and Local Air Monitoring Station
(SLAMS) monitor is allowable under certain conditions specified in 40
CFR 58.14 System Modification. These conditions provide state and local
air agencies multiple options by which they may propose, with
justification, for a monitor to be shut down. Whatever the
justification may be, each monitor proposed to be shut-down must go
through an established process to receive EPA Regional Administrator
approval for shut-down. As part of that process, the EPA Regional
Administrator provides opportunity for public comment before making a
decision to approve or disapprove the request. In conclusion, the EPA
believes that even without requirements for area-wide CO monitors
additional to the NCore sites, some number of area-wide monitors will
continue to operate into the future. EPA anticipates that monitors that
states find useful for other regulatory purposes, such as NEPA, would
be among the monitors that may continue to operate. The NCore sites,
along with monitors currently operating in the absence of other area-
wide monitoring requirements, will likely provide a sufficient set of
area-wide monitors to meet monitoring objectives.
The EPA also received a number of comments from transportation
groups, state and local groups, and an industry commenter (e.g., AAM,
AASHTO, NESCAUM, NYSDEC, NYSDOT, TXDOT, and VDOT) suggesting that
required near-road CO monitors should be paired with an area-wide CO
monitor within the same CBSA. For example, AASHTO recommended that ``*
* * EPA ensure that adequate coverage continues from neighborhood-scale
monitors to estimate background concentration levels, and that there is
at least one neighborhood scale monitor in every urbanized area that is
required to have a near-road monitor.'' NESCAUM recommended ``* * *
that EPA locate near-road CO monitors near urban NCore CO sites'' (as
noted above, NCore sites are area-wide sites by design).
The EPA recognizes that a pairing of near-road CO monitors with
area-wide CO monitors will provide information by which an estimate of
the difference between near-road concentrations to relative background
concentrations might be determined. As noted earlier, the Agency
believes that the combination of required NCore sites and those area-
wide monitors currently operating in the absence of minimum monitoring
requirements (of which many will likely continue operating in the
future) will largely fulfill the area-wide component of any near-road
site/area-wide site pairing in an urban area. An analysis of NCore site
locations (site data available from http://www.epa.gov/ttn/amtic/ncore/index.html), along with
[[Page 54318]]
all those area-wide CO monitors believed to be operating as of May 20,
2011 (utilizing EPA's Air Explorer Web tools located at http://www.epa.gov/airexplorer) indicated that of the 52 CBSAs with a
population of 1 million persons or more, based on 2010 Census data,,
only 4 are believed to be without an area-wide CO monitor.\33\ The EPA
believes that, based on the considerations discussed above, the
existing network will likely provide sufficient area-wide CO
concentration information on which a near-road to area-wide data
comparison could be based.
---------------------------------------------------------------------------
\33\ The EPA notes that of the 52 CBSAs that have 1 million or
more persons, 39 CBSAs contain an NCore monitoring station, which
includes a CO monitor.
---------------------------------------------------------------------------
f. Regional Administrator Authority
The EPA received a number of comments from states and
transportation groups (e.g., AASHTO, NYSDOT, TCEQ, TXDOT, and VDOT) on
the proposal for Regional Administrators to have the discretion to
require monitoring above the minimum requirements as necessary to
address situations where minimum monitoring requirements are not
sufficient to meet monitoring objectives. For example, AASHTO commented
that ``the proposed rule includes some examples of where additional
monitors may be necessary. AASHTO is concerned that these brief
examples may not be sufficient to ensure uniform application of this
additional authority among the EPA Regions,'' and that EPA should
provide guidance on this so that there is ``reasonable uniformity
between EPA Regions in the implementation of these provisions.'' TCEQ
commented that it ``does not agree that this discretion is appropriate,
particularly where EPA has not proposed a process by which Regional
Administrators must consult with states and the public regarding these
decisions.'' Further TCEQ stated that ``* * * the potential requirement
for additional monitors when `minimum monitoring requirements are not
sufficient to meet monitoring objectives' is overly broad and should be
refined to include objective criteria that will consistently applied
across all EPA Regions.''
The EPA notes that the authority of Regional Administrators to
require additional monitoring above the minimum required is not unique
to the CO NAAQS. For example, Regional Administrators have the
authority to use their discretion to require additional NO2,
lead, and sulfur dioxide monitors (40 CFR part 58 appendix D sections
4.3.4, 4.4.3, and 4.5, respectively) and to work with state and local
air agencies in designing and/or maintaining an appropriate ozone
monitoring network (40 CFR part 58 appendix D section 4.1). The EPA
believes that a nationally applicable network design may not always
account for all locations in every area where monitors may be
warranted. Example situations where the Regional Administrator
authority could be utilized, which were provided in the proposal, could
be for unmonitored locations where data or other information suggest
that CO concentrations may be approaching or exceeding the NAAQS due to
stationary CO sources, in downtown areas or urban street canyons, or in
areas that are subject to high ground-level CO concentrations
particularly due to or enhanced by topographical and meteorological
impacts. The Agency cannot anticipate every example that may exist
where the Regional Administrator authority might be used for inclusion
in this preamble text. However, the Agency believes it is important for
Regional Administrators to have the authority to address possible gaps
in the minimally required monitoring network in situations such as
those examples provided here. In response to public comments, the EPA
notes that Regional Administrators would use their authority in
collaboration with state agencies, working with stakeholders to design
and/or maintain the most appropriate CO monitoring network to meet the
needs of a given area. Finally, the Agency notes that any monitor
required by the Regional Administrator (or any new monitor proposed by
the state itself) is not done so with unfettered discretion. Any such
action would be included in the Annual Monitoring Network Plan per 40
CFR 58.10, and this plan must be made available for public inspection
and comment before any decisions are made by the EPA Regional
Administrator.
3. Conclusions on the Network Design
This section provides the rationale and details for the final
decision on changes to the CO monitoring network design and siting
criteria. As discussed above in section IV.B.2.a, motor vehicle
emissions are important contributors to ambient CO concentrations (REA,
section 2.2), contributing nearly 60% of the total CO emitted
nationally (per the 2008 NEI). As a result, microenvironments
influenced by on-road mobile sources are important contributors to
ambient CO exposures, particularly in urban areas (REA, section 2.7).
Therefore, the Administrator has concluded that monitoring in the near-
road environment to characterize and assess ambient CO concentrations
continues to be an appropriate objective for the CO monitoring network.
The EPA believes that the promulgation of minimum requirements for CO
monitors in the near-road environment is necessary to ensure a network
of adequate size and focus to provide data for comparison to the NAAQS,
support research which includes health studies, allow for model
verification, and fulfill multipollutant monitoring objectives.
Further, considering the lack of CO monitors assessing higher
trafficked roads in urban areas and CASAC's advice that the Agency
develop greater monitoring capacity for CO in near-road environments
(Brain and Samet, 2010b), the Agency believes that a number of CO
monitors should be focused in such locations. Highly trafficked roads
are expected to show elevated CO concentrations relative to area-wide
concentrations and to represent the locations where ambient CO
concentrations may be highest in an area. Regarding the locations where
required near-road CO monitors might be placed, the EPA proposed that
they be collocated with a subset of near-road NO2 monitors.
The EPA expects required near-road NO2 monitors (as
prescribed in 40 CFR part 58, appendix D, Section 4.3) to be adjacent
to highly trafficked roads within the CBSAs where they are required.
Recognizing this and also recognizing the benefits associated with
collocating monitors at the same site, the Agency is finalizing
requirements for CO monitors that will leverage required near-road
NO2 monitoring sites to house collocated near-road CO
monitors to create data for comparison to the NAAQS, support research
which includes health studies, provide data for model evaluation, and
foster the fulfillment of multipollutant objectives.
As noted in section IV.B.2.b above, after considering public
comments, EPA has modified the requirements for CO monitors from that
which was proposed so that only one CO monitor is required in each CBSA
in which near-road CO monitoring is required.\34\ This approach reduces
the total number of monitors that would have been required under the
proposal from 75 monitors within 52 CBSAs to 52 monitors within 52
CBSAs (based on 2010 Census data). The EPA believes this network design
addresses public comments while maintaining monitoring in a
sufficiently diverse set
[[Page 54319]]
of locations throughout 52 different urban areas around the country. By
having monitors within 52 different CBSAs, this network design is
expected to provide for monitoring in a wide range of diverse
situations with regard to traffic volumes, traffic patterns, roadway
designs, terrain/topography, meteorology, climate, as well as
surrounding land use and population characteristics.
---------------------------------------------------------------------------
\34\ This approach only requires one CO monitor to be installed
in those CBSAs that have two required near-road NO2
monitors.
---------------------------------------------------------------------------
The EPA is generally requiring CO monitors to be collocated with
near-road NO2 monitors. However, upon consideration of
public comments, the Agency is allowing flexibility for states to use
an alternate near-road location, which includes downtown areas, urban
street canyons, and other near-road locations. This flexibility is
provided for a required CO monitor, on a case-by-case basis, with EPA
Regional Administrator approval, when the state can provide
quantitative justification showing the expectation of higher peak CO
concentrations for that alternate location compared to a near-road
NO2 location. Such requests could be based upon appropriate
modeling, exploratory monitoring, or other methods, comparing the
alternative CO location and the near-road NO2 location.
In summary, based upon 2010 Census Bureau data this final rule will
require approximately 52 CO monitors to be collocated with near-road
NO2 monitors (or otherwise operated at an alternate, EPA
Regional Administrator approved, near-road location where peak CO
concentrations are expected) within 52 CBSAs that have populations of 1
million or more persons.
Regarding the deployment and operation of required CO monitors, the
Agency recognizes that many state and local air agencies are under
financial and related resource duress. EPA has concluded that allowing
additional time for installing CO monitors will provide an opportunity
for state and local agencies to work with EPA Regions to identify which
existing CO monitors may be appropriate to relocate to the near-road
locations. In many cases, EPA and the state may believe it is
appropriate to relocate monitors, including some of those that are
currently operated pursuant to existing maintenance plans. In these
cases, additional time may be necessary to allow states to revisit and
possibly revise, in consultation with (and subject to the approval of)
the EPA Regions, existing maintenance plans in a way that may allow
certain CO monitors to be free for relocation, if appropriate. Further,
if a state chooses to investigate whether it will request that a
required near-road CO monitor be sited in a near-road location other
than a required near-road NO2 site, the time allotted by the
final rule is expected to provide states with adequate time to perform
necessary analyses for submission to the Regional Administrator for
approval. Furthermore, EPA has concluded that public comments
suggesting a phased-in implementation, allowing for later stages to
benefit from experience in an initial round of monitor installations,
have merit.
As a result, the EPA has chosen not to require the implementation
of required CO sites by January 1, 2013 as was proposed. Instead, the
Agency is finalizing a two-phased implementation requirement. Those CO
monitors required within CBSAs having 2.5 million or more persons are
to be operational by January 1, 2015, although the Agency strongly
encourages the implementation of these required monitors as soon as
practicable. Those CO monitors required in CBSAs having 1 million or
more persons (and fewer than 2.5 million persons) are to be operational
by January 1, 2017. EPA intends to review the experience of states with
the first round of near-road CO monitors and the data produced by such
monitors and consider whether adjustments to the network requirements
are warranted. These required CO monitors shall be reflected in a
state's annual monitoring network plans due six months prior to
installation, i.e., on July 1, 2014 or July 1, 2016, respectively.
Regarding siting criteria, the EPA received public support to
adjust microscale CO siting criteria to match those of near-road
NO2 monitors (and microscale PM2.5 monitors). The
Agency also was urged to retain the existing microscale siting
criteria, for explicit use with microscale CO sites in downtown areas
or urban street canyon settings. As a result, the EPA is retaining the
existing siting criteria for microscale CO monitors in downtown areas
and urban street canyons and is finalizing the additional siting
criteria for those near-road microscale CO monitors outside of downtown
areas and urban street canyons to have probe height and horizontal
spacing to match those of near-road NO2 monitors as
prescribed in 40 CFR part 58 appendix E, sections 2, 4(d), 6.4(a), and
table E-4.
Specifically, the Agency is finalizing the following: (1) A
microscale near-road CO monitor inlet probe shall be between 2 and 7
meters above the ground; (2) a microscale CO monitor inlet probe in the
near-road environment shall be placed so it has an unobstructed air
flow, where no obstacles exist at or above the height of the monitor
probe, between the monitor probe and the outside nearest edge of the
traffic lanes of the target road segment; and (3) that CO monitors in
the near-road environment shall have inlet probes as near as
practicable to the outside nearest edge of the traffic lanes of the
target road segment, but shall not be located at a distance greater
than 50 meters in the horizontal from the outside nearest edge of the
traffic lanes of the target road segment.
Further, as suggested through public comments, the EPA is retaining
existing regulatory siting criteria language for microscale CO monitors
in downtown areas or urban street canyon locations, where: (1) The
inlet probe for a near-road microscale CO monitor in a downtown area or
urban street canyon shall be between 2.5 meters and 3.5 meters above
ground level; (2) the inlet probe for a near-road microscale CO monitor
in a downtown area or urban street canyon shall be within 10 meters
from the edge of the nearest traffic lane; and (3) near-road microscale
CO monitors in street canyons are required to be at least 10 meters
from an intersection.
Finally, the EPA recognizes that a monitoring network design may
not always require monitoring on a national scale that is sufficient in
fulfilling specific or otherwise unique data needs or monitoring
objectives for every area across the nation. Thus, the EPA is
finalizing the provision that EPA Regional Administrators have the
authority to require monitoring above the minimum requirements, as
necessary, in any area, to address situations where the minimally
required monitoring network is not sufficient to meet monitoring
objectives. Example situations where the Regional Administrator
Authority could be utilized include, but are not limited to, those
unmonitored locations where data or other information suggest that CO
concentrations may be approaching or exceeding the NAAQS due to
stationary CO sources, in downtown areas or urban street canyons, or in
areas that are subject to high ground-level CO concentrations
particularly due to or enhanced by topographical and meteorological
impacts. In all cases in which a Regional Administrator may consider
the need for additional monitoring, it is expected that the Regional
Administrators will work with the state or local air agencies to
evaluate evidence or needs to determine whether a particular area may
warrant additional monitoring.
[[Page 54320]]
V. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
Under Executive Order 12866 (58 FR 51735, October 4, 1993), this
action is a ``significant regulatory action'' because it was deemed to
``raise novel legal or policy issues.'' Accordingly, EPA submitted this
action to the Office of Management and Budget (OMB) for review under
Executive Orders 12866 and 13563 (76 FR 3821, January 21, 2011) and any
changes made in response to OMB recommendations have been documented in
the docket for this action.
B. Paperwork Reduction Act
The information collection requirements in this final rule have
been submitted for approval to the Office of Management and Budget
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The
information collection requirements are not enforceable until OMB
approves them. The Information Collection Request (ICR) document
prepared by EPA for these revisions to part 58 has been assigned EPA
ICR number 0940.24.
The information collected under 40 CFR part 53 (e.g., test results,
monitoring records, instruction manual, and other associated
information) is needed to determine whether a candidate method intended
for use in determining attainment of the NAAQS in 40 CFR part 50 will
meet comparability requirements for designation as a FRM or FEM. We do
not expect the number of FRM or FEM determinations to increase over the
number that is currently used to estimate burden associated with CO
FRM/FEM determinations provided in the current ICR for 40 CFR part 53
(EPA ICR numbers 0940.24). As such, no change in the burden estimate
for 40 CFR part 53 has been made as part of this rulemaking.
The information collected and reported under 40 CFR part 58 is
needed to determine compliance with the NAAQS, to characterize air
quality and associated health impacts, to develop emissions control
strategies, and to measure progress for the air pollution program. The
amendments would revise the technical requirements for CO monitoring
sites, require the relocation or siting of ambient CO air monitors, and
the reporting of the collected ambient CO monitoring data to EPA's Air
Quality System (AQS). The annual average reporting burden for the
collection under 40 CFR part 58 (averaged over the first 3 years of
this ICR) for a network of 311 CO monitors is $7,235,483. Burden is
defined at 5 CFR 1320.3(b). State, local, and Tribal entities are
eligible for State assistance grants provided by the Federal government
under the CAA which can be used for monitors and related activities.
An agency may not conduct or sponsor, and a person is not required
to respond to, a collection of information unless it displays a
currently valid OMB control number. The OMB control numbers for EPA's
regulations in 40 CFR are listed in 40 CFR part 9. When this ICR is
approved by OMB, the Agency will publish a technical amendment to 40
CFR part 9 in the Federal Register to display the OMB control number
for the approved information collection requirements contained in this
final rule.
C. Regulatory Flexibility Act
The Regulatory Flexibility Act (RFA) generally requires an agency
to prepare a regulatory flexibility analysis of any rule subject to
notice and comment rulemaking requirements under the Administrative
Procedure Act or any other statute unless the agency certifies that the
rule will not have a significant economic impact on a substantial
number of small entities. Small entities include small businesses,
small organizations, and small governmental jurisdictions.
For purposes of assessing the impacts of today's rule on small
entities, small entity is defined as: (1) A small business that is a
small industrial entity as defined by the Small Business
Administration's (SBA) regulations at 13 CFR 121.201; (2) a small
governmental jurisdiction that is a government of a city, county, town,
school district or special district with a population of less than
50,000; and (3) a small organization that is any not-for-profit
enterprise which is independently owned and operated and is not
dominant in its field.
After considering the economic impacts of this final rule on small
entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities. This final
rule will not impose any requirements on small entities. Rather, this
rule retains existing national standards for allowable concentrations
of CO in ambient air as required by section 109 of the CAA. See also
American Trucking Associations v. EPA. 175 F. 3d at 1044-45 (NAAQS do
not have significant impacts upon small entities because NAAQS
themselves impose no regulations upon small entities). Similarly, the
amendments to 40 CFR part 58 address the requirements for States to
collect information and report compliance with the NAAQS and will not
impose any requirements on small entities.
D. Unfunded Mandates Reform Act
This rule does not contain a Federal mandate that may result in
expenditures of $100 million or more for State, local, and Tribal
governments, in the aggregate, or the private sector in any one year.
This rule retains the existing national ambient air quality standards
for carbon monoxide. The expected costs associated with the monitoring
requirements are described in EPA's ICR document, but those costs are
expected to be well less than $100 million (adjusted for inflation) in
the aggregate for any year. Furthermore, as indicated previously, in
setting a NAAQS, EPA cannot consider the economic or technological
feasibility of attaining ambient air quality standards. Thus, this rule
is not subject to the requirements of sections 202 or 205 of the UMRA.
This rule is also not subject to the requirements of section 203 of
the UMRA because it imposes no enforceable duty on any small
governments.
E. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government, as
specified in Executive Order 13132. The rule does not alter the
relationship between the Federal government and the States regarding
the establishment and implementation of air quality improvement
programs as codified in the CAA. Under section 109 of the CAA, EPA is
mandated to establish and review NAAQS; however, CAA section 116
preserves the rights of States to establish more stringent requirements
if deemed necessary by a State. Furthermore, this rule does not impact
CAA section 107 which establishes that the States have primary
responsibility for implementation of the NAAQS. Finally, as noted in
section D (above) on UMRA, this rule does not impose significant costs
on State, local or Tribal governments or the private sector. Thus,
Executive Order 13132 does not apply to this rule.
[[Page 54321]]
F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
This action does not have Tribal implications, as specified in
Executive Order 13175 (65 FR 67249, November 9, 2000). It does not have
a substantial direct effect on one or more Indian Tribes, since Tribes
are not obligated to adopt or implement any NAAQS. Thus, Executive
Order 13175 does not apply to this action.
G. Executive Order 13045: Protection of Children From Environmental
Health and Safety Risks
This action is not subject to EO 13045 (62 FR 19885, April 23,
1997) because it is not economically significant as defined in EO
12866, and because the Agency does not believe the environmental health
or safety risks addressed by this action present a disproportionate
risk to children. This action's health and risk assessments are
described in section II.A.
H. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution or Use
This action is not a ``significant energy action'' as defined in
Executive Order 13211 (66 FR 28355 (May 22, 2001)) because it is not
likely to have a significant adverse effect on the supply,
distribution, or use of energy. The rule concerns the review of the
NAAQS for CO. The rule does not prescribe specific pollution control
strategies by which these ambient standards will be met. Such
strategies are developed by States on a case-by-case basis, and EPA
cannot predict whether the control options selected by States will
include regulations on energy suppliers, distributors, or users.
I. National Technology Transfer and Advancement Act
Section 12(d) of the National Technology Transfer and Advancement
Act of 1995 (NTTAA), Public Law 104- 113, section 12(d) (15 U.S.C. 272
note) directs EPA to use voluntary consensus standards in its
regulatory activities unless to do so would be inconsistent with
applicable law or otherwise impractical. Voluntary consensus standards
are technical standards (e.g., materials specifications, test methods,
sampling procedures, and business practices) that are developed or
adopted by voluntary consensus standards bodies. The NTTAA directs EPA
to provide Congress, through OMB, explanations when the Agency decides
not to use available and applicable voluntary consensus standards.
This rulemaking involves technical standards with regard to ambient
monitoring of CO. We have not identified any potentially applicable
voluntary consensus standards that would adequately characterize
ambient CO concentrations for the purposes of determining compliance
with the CO NAAQS and none have been brought to our attention in
comments. Therefore, EPA has decided to use the method ``Measurement
Principle and Calibration Procedure for the Measurement of Carbon
Monoxide in the Atmosphere (Non-Dispersive Infrared Photometry)'' (40
CFR part 50, appendix C), as revised by this action, for the purposes
of ambient monitoring of CO concentrations.
J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations
Executive Order 12898 (59 FR 7629 (Feb. 16, 1994)) establishes
Federal executive policy on environmental justice. Its main provision
directs Federal agencies, to the greatest extent practicable and
permitted by law, to make environmental justice part of their mission
by identifying and addressing, as appropriate, disproportionately high
and adverse human health or environmental effects of their programs,
policies, and activities on minority populations and low-income
populations in the United States.
EPA has determined that this final rule will not have
disproportionately high and adverse human health or environmental
effects on minority or low-income populations because it does not
affect the level of protection provided to human health or the
environment. The action in this notice is to retain without revision
the existing NAAQS for CO. Therefore this action will not cause
increases in source emissions or air concentrations.
K. Congressional Review Act
The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the
Small Business Regulatory Enforcement Fairness Act of 1996, generally
provides that before a rule may take effect, the agency promulgating
the rule must submit a rule report, which includes a copy of the rule,
to each House of the Congress and to the Comptroller General of the
United States. EPA will submit a report containing this rule and other
required information to the U.S. Senate, the U.S. House of
Representatives, and the Comptroller General of the United States prior
to publication of the rule in the Federal Register. A major rule cannot
take effect until 60 days after it is published in the Federal
Register. This action is not a ``major rule'' as defined by 5 U.S.C.
804(2). This rule will be effective October 31, 2011.
References
Adams K.F.; Koch G.; Chatterjee B.; Goldstein G.M.; O'Neil J.J.;
Bromberg P.A.; Sheps D.S.; McAllister S.; Price C.J.; Bissette J.
(1988) Acute elevation of blood carboxyhemoglobin to 6% impairs
exercise performance and aggravates symptoms in patients with
ischemic heart disease. J. Am. Coll. Cardiol. 12:900-909.
Allred E.N.; Bleecker E.R.; Chaitman B.R.; Dahms T.E.; Gottlieb
S.O.; Hackney J.D.; Pagano M.; Selvester R.H.; Walden S.M.; Warren
J. (1989a) Short-term effects of carbon monoxide exposure on the
exercise performance of subjects with coronary artery disease. N.
Engl. J. Med. 321:1426-1432.
Allred E.N.; Bleecker,E.R.; Chaitman B.R.; Dahms T.E.; Gottlieb
S.O.; Hackney J.D.; Hayes D.; Pagano M.; Selvester R.H.; Walden
S.M.; Warren J. (1989b) Acute effects of carbon monoxide exposure on
individuals with coronary artery disease. Cambridge, MA: Health
Effects Institute; research report no. 25.
Allred E.N.; Bleecker E.R.; Chaitman B.R.; Dahms T.E.; Gottlieb
S.O.; Hackney J.D.; Pagano M.; Selvester R.H.; Walden S.M.; Warren
J. (1991) Effects of carbon monoxide on myocardial ischemia.
Environ. Health Perspect. 91:89-132.
AHA. (2003) Heart and Stroke Facts. American Heart Association,
Dallas, TX. Available at: http://www.americanheart.org/downloadable/heart/1056719919740HSFacts2003text.pdf.
Anderson E.W.; Andelman R.J.; Strauch J.M.; Fortuin N.J. and
Knelson, J.H. (1973) Effect of low level carbon monoxide exposure on
onset and duration of angina pectoris. Annals of Internal Medicine
79:46-50.
Baldauf R.; Thoma E.; Hays M.; Shores R.; Kinsey J.; Gullett B.;
Kimbrough S.; Isakov V.; Long T.; Snow R.; Khlystov A.; Weinstein
J.; Chen F.L.; Seila R.; Olson D.; Gilmour I.; Cho S.H.; Watkins N.;
Rowley P.; Bang J. (2008a). Traffic and meteorological impacts on
near-road air quality: Summary of methods and trends from the
Raleigh near-road study. J Air Waste Manag Assoc, 58:865-878. 190239
Baldauf R.; Thoma E.; Khlystov A.; Isakov V.; Bowker G.; Long T.;
Snow R. (2008b). Impacts of noise barriers on near-road air quality.
Atmos Environ, 42:7502-7507.
Bell M.L.; Peng R.D.; Dominici F.; Samet J.M. (2009) Emergency
admissions for cardiovascular disease and ambient levels of carbon
monoxide: Results for 126 U.S. urban counties, 1999-2005.
Circulation, 120:949-955.
Bissette J.; Carr G.; Koch G.G.; Adams K.F.; Sheps D.S. (1986)
Analysis of (events/time at risk) ratios from two period crossover
studies. In: American Statistical Association 1986 proceedings of
the Biopharmaceutical Section; August; Chicago, IL., Washington, DC:
[[Page 54322]]
American Statistical Asssociation; pp. 104-108.
Brain, J.D. (2009) Letter from Dr. J.D. Brain to Administrator Lisa
Jackson. Re: Consultation on EPA's Carbon Monoxide National Ambient
Air Quality Standards: Scope and Methods Plan for Health Risk and
Exposure Assessment. CASAC-09-012. July 14, 2009.
Brain J. and Samet J. (2009) Letter from Drs. J.D. Brain and J.M.
Samet to Administrator Lisa Jackson. Re: Review of EPA's Integrated
Science Assessment for Carbon Monoxide (First External Review Draft)
EPA-CASAC-09-011. June 24, 2009.
Brain, J.D. and Samet, J.M. (2010a) Letter from Drs. J.D. Brain and
J.M. Samet to Administrator Lisa Jackson. Re: Review of the Risk and
Exposure Assessment to Support the Review of the Carbon Monoxide
(CO) Primary National Ambient Air Quality Standards: First External
Review Draft. EPA-CASAC-10-006. February 12, 2010.
Brain J.D. and Samet J.M. (2010b) Letter from Drs. J.D. Brain and
J.M. Samet to Administrator Lisa Jackson. Re: Review of the Risk and
Exposure Assessment to Support the Review of the Carbon Monoxide
(CO) Primary National Ambient Air Quality Standards: Second External
Review Draft. EPA-CASAC-10-012. May 19, 2010.
Brain J.D. and Samet J.M. (2010c) Letter from Drs. J.D. Brain and
J.M. Samet to Administrator Lisa Jackson. Re: Review of the Policy
Assessment for the Review of the Carbon Monoxide National Ambient
Air Quality Standards (NAAQS): External Review Draft. EPA-CASAC-10-
013. June 8, 2010.
Brain J.D. and Samet J.M. (2010d) Letter from Drs. J.D. Brain and
J.M. Samet to Administrator Lisa Jackson. Re: Review of Integrated
Science Assessment for Carbon Monoxide (Second External Review
Draft). EPA-CASAC-10-005. January 20, 2010.
Henderson R. (2008) Letter from Dr. Rogene Henderson, Chairman,
Clean Air Scientific Advisory Committee, to Administrator Stephen
Johnson. Re: Consultation on EPA's Draft Plan for Review of the
Primary NAAQS for Carbon Monoxide CASAC-08-013. June 12, 2008.
Johnson T.; Capel J.; Paul R.; Wijnberg L. (1992) Estimation of
Carbon Monoxide Exposure and associated Carboxyhemoglobin levels in
Denver Residents Using a Probabalistic verion of NEM, prepared by
International Technology for U.S. EPA, Office of Air Quality
Planning and Standards, Durham, NC, Contract No. 68-D0-0062.
Johnson T.; Mihlan G.; LaPointe J.; Fletcher K.; Capel J. (2000)
Estimation of Carbon Monoxide Exposures and Associated
Carboxyhemoglobin Levels for Residents of Denver and Los Angeles
Using pNEM/CO (Version 2.1). Report prepared by ICF Consulting and
TRJ Environmental, Inc., under EPA Contract No. 68-D6-0064. U.S.
Environmental Protection Agency, Research Triangle Park, North
Carolina. Available at: http://www.epa.gov/ttn/fera/human_related.html. June 2000.
Kleinman M.T.; Davidson D.M.; Vandagriff R.B.; Caiozzo V.J.;
Whittenberger J.L. (1989) Effects of short-term exposure to carbon
monoxide in subjects with coronary artery disease. Arch. Environ.
Health 44:361-369.
Kleinman M.T.; Leaf D.A.; Kelly E.; Caiozzo V.; Osann K.; O'Niell T.
(1998) Urban angina in the mountains: effects of carbon monoxide and
mild hypoxemia on subjects with chronic stable angina. Arch.
Environ. Health 53:388-397.
Koken P.J.M.; Piver W.T.; Ye F.; Elixhauser A.; Olsen L.M.; Portier
C.J. (2003) Temperature, air pollution, and hospitalization for
cardiovascular diseases among elderly people in Denver. Environ
Health Perspect, 111:1312-1317.
Lippmann, M. (1984) CASAC Findings and Recommendations on the
Scientific Basis for a Revised NAAQS for Carbon Monoxide. [Letter to
W.D. Ruckelshous, EPA Administrator]. May 17.
Linn W.S.; Szlachcic Y.; Gong H. Jr; Kinney P.L.; Berhane K.T.
(2000) Air pollution and daily hospital admissions in metropolitan
Los Angeles. Environ Health Perspect, 108:427-434.
Mann J.K.; Tager I.B.; Lurmann F.; Segal M.; Quesenberry C.P. Jr;
Lugg M.M.; Shan J.; Van den Eeden S.K. (2002) Air pollution and
hospital admissions for ischemic heart disease in persons with
congestive heart failure or arrhythmia. Environ Health Perspect,
110:1247-1252.
Metzger K.B.; Tolbert P.E.; Klein M.; Peel J.L.; Flanders W.D.; Todd
K.H.; Mulholland J.A.; Ryan P.B.; Frumkin H. (2004) Ambient air
pollution and cardiovascular emergency department visits.
Epidemiology, 15:46-56.
National Research Council. (2003) Managing Carbon Monoxide Pollution
in Meteorological and Topographical Problem Areas. The National
Academies Press, Washington, DC.
Sheps D.S.; Adams K.F. Jr.; Bromberg P.A.; Goldstein G.M.; O'Neil
J.J.; Horstman D.; Koch G. (1987) Lack of effect of low levels of
carboxyhemoglobin on cardiovascular function in patients with
ischemic heart disease. Arch. Environ. Health 42:108-116.
Symons J.M.; Wang L.; Guallar E.; Howell E.; Dominici F.; Schwab M.;
Ange B.A.; Samet J.; Ondov J.; Harrison D.; Geyh A. (2006) A case-
crossover study of fine particulate matter air pollution and onset
of congestive heart failure symptom exacerbation leading to
hospitalization. Am J Epidemiol, 164:421-433.
Tolbert P.E.; Klein M.; Peel J.L.; Sarnat S.E.; Sarnat J.A. (2007)
Multipollutant modeling issues in a study of ambient air quality and
emergency department visits in Atlanta. J Expo Sci Environ
Epidemiol, 17:S29-S35.
U.S. Environmental Protection Agency. (1979a) Air Quality Criteria
for Carbon Monoxide. Office of Health and Environmental Assessment,
Environmental Criteria and Assessment Office, Research Triangle
Park, NC. EPA-600/8-79-022.
U.S. Environmental Protection Agency. (1979b) Assessment of Adverse
Health Effects from Carbon Monoxide and Implications for Possible
Modifications of the Standard. Office of Air Quality Planning and
Standards, Research Triangle Park, NC.
U.S. Environmental Protection Agency. (1984a) Revised Evaluation of
Health Effects Associated with Carbon Monoxide Exposure: An Addendum
to the 1979 EPA Air Quality Criteria Document for Carbon Monoxide.
Office of Health and Environmental Assessment, Environmental
Criteria and Assessment Office, Research Triangle Park, NC. EPA-600/
8-83-033F.
U.S. Environmental Protection Agency. (1984b) Review of the NAAQS
for Carbon Monoxide: Reassessment of Scientific and Technical
Information. Office of Air Quality Planning and Standards, Research
Triangle Park. NC. EPA-450/584-904.
U.S. Environmental Protection Agency. (1991) Air Quality Criteria
for Carbon Monoxide. Office of Health and Environmental Assessment,
Environmental Criteria and Assessment Office, Research Triangle
Park, NC. EPA/600/8-90/045F. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_pr.html.
U.S. Environmental Protection Agency. (1992) Review of the National
Ambient Air Quality Standards for Carbon Monoxide: Assessment of
Scientific and Technical Information, OAQPS Staff Paper. Office of
Air Quality Planning and Standards, Research Triangle Park, NC. EPA/
452/R-92-004.
U.S. Environmental Protection Agency. (2000) Air Quality Criteria
for Carbon Monoxide. National Center for Environmental Assessment,
Office of Research and Development, Research Triangle Park, NC. EPA/
600/P-99/001F. Available at: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=18163.
U.S. Environmental Protection Agency. (2008a) Draft Plan for Review
of the National Ambient Air Quality Standards for Carbon Monoxide.
Also known as Draft Integrated Review Plan. National Center for
Environmental Assessment and Office of Air Quality Planning and
Standards, Research Triangle Park, NC. EPA-452/D-08-001. Available
at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pd.html.
U.S. Environmental Protection Agency. (2008b) Plan for Review of the
National Ambient Air Quality Standards for Carbon Monoxide. Also
known as Integrated Review Plan. National Center for Environmental
Assessment and Office of Air Quality Planning and Standards,
Research Triangle Park, NC. EPA-452/R-08-005. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pd.html.
U.S. Environmental Protection Agency. (2009a) Integrated Science
Assessment for Carbon Monoxide, First External Review Draft.
National Center for Environmental Assessment, Research
[[Page 54323]]
Triangle Park, NC. EPA/600/R-00/019. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_isa.html.
U.S. Environmental Protection Agency. (2009b) Integrated Science
Assessment for Carbon Monoxide, Second External Review Draft.
National Center for Environmental Assessment, Research Triangle
Park, NC. EPA/600/R-09/019B. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_isa.html.
U.S. Environmental Protection Agency. (2009c) Carbon Monoxide
National Ambient Air Quality Standards: Scope and Methods Plan for
Health Risk and Exposure Assessment. Draft. Office of Air Quality
Planning and Standards, Research Triangle Park, NC. EPA-452/R-09-
004. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pd.html.
U.S. Environmental Protection Agency. (2009d) Risk and Exposure
Assessment to Support the Review of the Carbon Monoxide Primary
National Ambient Air Quality Standards, First External Review Draft.
Office of Air Quality Planning and Standards, Research Triangle
Park, NC. EPA-452/P-09-008. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_rea.html.
U.S. Environmental Protection Agency. (2010a) Integrated Science
Assessment for Carbon Monoxide. National Center for Environmental
Assessment, Research Triangle Park, NC. EPA/600/R-09/019F. Available
at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_isa.html.
U.S. Environmental Protection Agency. (2010b) Quantitative Risk and
Exposure Assessment for Carbon Monoxide--Amended. Office of Air
Quality Planning and Standards, Research Triangle Park, NC. EPA-452/
R-10-009. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_rea.html.
U.S. Environmental Protection Agency. (2010c) Policy Assessment for
the Review of the Carbon Monoxide National Ambient Air Quality
Standards. Office of Air Quality Planning and Standards, Research
Triangle Park, NC. EPA 452/R-10-007. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pa.html.
U.S. Environmental Protection Agency. (2010d) Risk and Exposure
Assessment to Support the Review of the Carbon Monoxide Primary
National Ambient Air Quality Standards, Second External Review
Draft, U.S Environmental Protection Agency, Research Triangle Park,
NC, report no. EPA-452/P-10-004. Available at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_rea.html.
U.S. Environmental Protection Agency. (2010e) Policy Assessment for
the Review of the Carbon Monoxide National Ambient Air Quality
Standards, External Review Draft. Office of Air Quality Planning and
Standards, Research Triangle Park, NC. EPA-452/P-10-005. Available
at: http://www.epa.gov/ttn/naaqs/standards/co/s_co_cr_pa.html.
Watkins N. and Thompson R. (2010) CO Monitoring Network Background
and Review. Memorandum to the Carbon Monoxide NAAQS Review Docket.
EPA-HQ-OAR-2008-0015.
Wellenius G.A.; Bateson T.F.; Mittleman M.A.; Schwartz J. (2005)
Particulate air pollution and the rate of hospitalization for
congestive heart failure among medicare beneficiaries in Pittsburgh,
Pennsylvania. Am J Epidemiol 161:1030-1036.
Zhu Y.; Hinds W.C.; Kim S.; Shen S.; Sioutas C. (2002) Study of
ultrafine particles near a major highway with heavy-duty diesel
traffic. Atmos Environ, 36:4323-4335.
List of Subjects
40 CFR Part 50
Environmental protection, Air pollution control, Carbon monoxide,
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.
40 CFR Part 53
Environmental protection, Administrative practice and procedure,
Air pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements.
40 CFR Part 58
Environmental protection, Administrative practice and procedure,
Air pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements.
Dated: August 12, 2011.
Lisa P. Jackson,
Administrator.
For the reasons stated in the preamble, title 40, chapter I of the
Code of Federal Regulations is amended as follows:
PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY
STANDARDS
0
1. The authority citation for part 50 continues to read as follows:
Authority: 42 U.S.C. 7401, et seq.
0
2. Appendix C to part 50 is revised to read as follows:
Appendix C to Part 50--Measurement Principle and Calibration Procedure
for the Measurement of Carbon Monoxide in the Atmosphere (Non-
Dispersive Infrared Photometry)
1.0 Applicability
1.1 This non-dispersive infrared photometry (NDIR) Federal
Reference Method (FRM) provides measurements of the concentration of
carbon monoxide (CO) in ambient air for determining compliance with
the primary and secondary National Ambient Air Quality Standards
(NAAQS) for CO as specified in Sec. 50.8 of this chapter. The
method is applicable to continuous sampling and measurement of
ambient CO concentrations suitable for determining 1-hour or longer
average measurements. The method may also provide measurements of
shorter averaging times, subject to specific analyzer performance
limitations. Additional CO monitoring quality assurance procedures
and guidance are provided in part 58, appendix A, of this chapter
and in reference 1 of this appendix C.
2.0 Measurement Principle
2.1 Measurements of CO in ambient air are based on automated
measurement of the absorption of infrared radiation by CO in an
ambient air sample drawn into an analyzer employing non-wavelength-
dispersive, infrared photometry (NDIR method). Infrared energy from
a source in the photometer is passed through a cell containing the
air sample to be analyzed, and the quantitative absorption of energy
by CO in the sample cell is measured by a suitable detector. The
photometer is sensitized specifically to CO by employing CO gas in a
filter cell in the optical path, which, when compared to a
differential optical path without a CO filter cell, limits the
measured absorption to one or more of the characteristic wavelengths
at which CO strongly absorbs. However, to meet measurement
performance requirements, various optical filters, reference cells,
rotating gas filter cells, dual-beam configurations, moisture traps,
or other means may also be used to further enhance sensitivity and
stability of the photometer and to minimize potential measurement
interference from water vapor, carbon dioxide (CO2), or
other species. Also, various schemes may be used to provide a
suitable zero reference for the photometer, and optional automatic
compensation may be provided for the actual pressure and temperature
of the air sample in the measurement cell. The measured infrared
absorption, converted to a digital reading or an electrical output
signal, indicates the measured CO concentration.
2.2 The measurement system is calibrated by referencing the
analyzer's CO measurements to CO concentration standards traceable
to a National Institute of Standards and Technology (NIST) primary
standard for CO, as described in the associated calibration
procedure specified in section 4 of this reference method.
2.3 An analyzer implementing this measurement principle will be
considered a reference method only if it has been designated as a
reference method in accordance with part 53 of this chapter.
2.4 Sampling considerations. The use of a particle filter in the
sample inlet line of a CO FRM analyzer is optional and left to the
discretion of the user unless such a filter is specified or
recommended by the analyzer manufacturer in the analyzer's
associated operation or instruction manual.
3.0 Interferences
3.1 The NDIR measurement principle is potentially susceptible to
interference from water vapor and CO2, which have some
infrared absorption at wavelengths in common with CO and normally
exist in the atmosphere. Various instrumental techniques can be used
to effectively minimize these interferences.
[[Page 54324]]
4.0 Calibration Procedures
4.1 Principle. Either of two methods may be selected for dynamic
multipoint calibration of FRM CO analyzers, using test gases of
accurately known CO concentrations obtained from one or more
compressed gas cylinders certified as CO transfer standards:
4.1.1 Dilution method: A single certified standard cylinder of
CO is quantitatively diluted as necessary with zero air to obtain
the various calibration concentration standards needed.
4.1.2 Multiple-cylinder method: Multiple, individually certified
standard cylinders of CO are used for each of the various
calibration concentration standards needed.
4.1.3 Additional information on calibration may be found in
Section 12 of reference 1.
4.2 Apparatus. The major components and typical configurations
of the calibration systems for the two calibration methods are shown
in Figures 1 and 2. Either system may be made up using common
laboratory components, or it may be a commercially manufactured
system. In either case, the principal components are as follows:
4.2.1 CO standard gas flow control and measurement devices (or a
combined device) capable of regulating and maintaining the standard
gas flow rate constant to within 2 percent and
measuring the gas flow rate accurate to within 2
percent, properly calibrated to a NIST-traceable standard.
4.2.2 For the dilution method (Figure 1), dilution air flow
control and measurement devices (or a combined device) capable of
regulating and maintaining the air flow rate constant to within
2 percent and measuring the air flow rate accurate to
within 2 percent, properly calibrated to a NIST-
traceable standard.
4.2.3 Standard gas pressure regulator(s) for the standard CO
cylinder(s), suitable for use with a high-pressure CO gas cylinder
and having a non-reactive diaphragm and internal parts and a
suitable delivery pressure.
4.2.4 Mixing chamber for the dilution method of an inert
material and of proper design to provide thorough mixing of CO
standard gas and diluent air streams.
4.2.5 Output sampling manifold, constructed of an inert material
and of sufficient diameter to ensure an insignificant pressure drop
at the analyzer connection. The system must have a vent designed to
ensure nearly atmospheric pressure at the analyzer connection port
and to prevent ambient air from entering the manifold.
4.3 Reagents
4.3.1 CO gas concentration transfer standard(s) of CO in air,
containing an appropriate concentration of CO suitable for the
selected operating range of the analyzer under calibration and
traceable to a NIST standard reference material (SRM). If the CO
analyzer has significant sensitivity to CO2, the CO
standard(s) should also contain 350 to 400 ppm CO2 to
replicate the typical CO2 concentration in ambient air.
However, if the zero air dilution ratio used for the dilution method
is not less than 100:1 and the zero air contains ambient levels of
CO2, then the CO standard may be contained in nitrogen
and need not contain CO2.
4.3.2 For the dilution method, clean zero air, free of
contaminants that could cause a detectable response on or a change
in sensitivity of the CO analyzer. The zero air should contain < 0.1
ppm CO.
4.4 Procedure Using the Dilution Method
4.4.1 Assemble or obtain a suitable dynamic dilution calibration
system such as the one shown schematically in Figure 1. Generally,
all calibration gases including zero air must be introduced into the
sample inlet of the analyzer. However, if the analyzer has special,
approved zero and span inlets and automatic valves to specifically
allow introduction of calibration standards at near atmospheric
pressure, such inlets may be used for calibration in lieu of the
sample inlet. For specific operating instructions, refer to the
manufacturer's manual.
4.4.2 Ensure that there are no leaks in the calibration system
and that all flowmeters are properly and accurately calibrated,
under the conditions of use, if appropriate, against a reliable
volume or flow rate standard such as a soap-bubble meter or wet-test
meter traceable to a NIST standard. All volumetric flow rates should
be corrected to the same temperature and pressure such as 298.15 K
(25 [deg]C) and 760 mm Hg (101 kPa), using a correction formula such
as the following:
[GRAPHIC] [TIFF OMITTED] TR31AU11.001
Where:
Fc = corrected flow rate (L/min at 25 [deg]C and 760 mm Hg),
Fm = measured flow rate (at temperature Tm and pressure Pm),
Pm = measured pressure in mm Hg (absolute), and
Tm = measured temperature in degrees Celsius.
4.4.3 Select the operating range of the CO analyzer to be
calibrated. Connect the measurement signal output of the analyzer to
an appropriate readout instrument to allow the analyzer's
measurement output to be continuously monitored during the
calibration. Where possible, this readout instrument should be the
same one used to record routine monitoring data, or, at least, an
instrument that is as closely representative of that system as
feasible.
4.4.4 Connect the inlet of the CO analyzer to the output-
sampling manifold of the calibration system.
4.4.5 Adjust the calibration system to deliver zero air to the
output manifold. The total air flow must exceed the total demand of
the analyzer(s) connected to the output manifold to ensure that no
ambient air is pulled into the manifold vent. Allow the analyzer to
sample zero air until a stable response is obtained. After the
response has stabilized, adjust the analyzer zero reading.
4.4.6 Adjust the zero air flow rate and the CO gas flow rate
from the standard CO cylinder to provide a diluted CO concentration
of approximately 80 percent of the measurement upper range limit
(URL) of the operating range of the analyzer. The total air flow
rate must exceed the total demand of the analyzer(s) connected to
the output manifold to ensure that no ambient air is pulled into the
manifold vent. The exact CO concentration is calculated from:
[GRAPHIC] [TIFF OMITTED] TR31AU11.002
Where:
[CO]OUT = diluted CO concentration at the output manifold (ppm),
[CO]STD = concentration of the undiluted CO standard (ppm),
FCO = flow rate of the CO standard (L/min), and
FD = flow rate of the dilution air (L/min).
Sample this CO concentration until a stable response is obtained.
Adjust the analyzer span control to obtain the desired analyzer
response reading equivalent to the calculated standard
concentration. If substantial adjustment of the analyzer span
control is required, it may be necessary to recheck the zero and
span adjustments by repeating steps 4.4.5 and 4.4.6. Record the CO
concentration and the analyzer's final response.
4.4.7 Generate several additional concentrations (at least three
evenly spaced points across the remaining scale are suggested to
verify linearity) by decreasing FCO or increasing FD. Be sure the
total flow exceeds the analyzer's total flow demand. For each
concentration generated, calculate the exact CO concentration using
equation (2). Record the concentration and the analyzer's stable
response for each concentration. Plot the analyzer responses
(vertical or y-axis) versus the corresponding CO concentrations
(horizontal or x-axis). Calculate the linear regression slope and
intercept of the calibration curve and verify that no point deviates
from this line by more than 2 percent of the highest concentration
tested.
4.5 Procedure Using the Multiple-Cylinder Method. Use the
procedure for the dilution method with the following changes:
4.5.1 Use a multi-cylinder, dynamic calibration system such as
the typical one shown in Figure 2.
4.5.2 The flowmeter need not be accurately calibrated, provided
the flow in the output manifold can be verified to exceed the
analyzer's flow demand.
4.5.3 The various CO calibration concentrations required in
Steps 4.4.5, 4.4.6, and 4.4.7 are obtained without dilution by
selecting zero air or the appropriate certified standard cylinder.
4.6 Frequency of Calibration. The frequency of calibration, as
well as the number of points necessary to establish the calibration
curve and the frequency of other performance checking, will vary by
analyzer. However, the minimum frequency, acceptance criteria, and
subsequent actions are specified in reference 1, appendix D,
``Measurement Quality Objectives and Validation Template for CO''
(page 5 of 30). The user's quality control program should provide
guidelines for initial establishment of these variables and for
subsequent alteration as operational experience is accumulated.
Manufacturers of CO analyzers should include in their instruction/
operation manuals information and guidance as to these variables and
on other matters of operation, calibration, routine maintenance, and
quality control.
[[Page 54325]]
5.0 Reference
1. QA Handbook for Air Pollution Measurement Systems--Volume II.
Ambient Air Quality Monitoring Program. U.S. EPA. EPA-454/B-08-003
(2008).
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TR31AU11.003
[[Page 54326]]
[GRAPHIC] [TIFF OMITTED] TR31AU11.004
BILLING CODE 6560-50-C
PART 53--AMBIENT AIR QUALITY REFERENCE AND EQUIVALENT METHODS
0
3. The authority citation for part 53 continues to read as follows:
Authority: 42 U.S.C. 7401, et seq.
0
4. Subpart B of part 53 is revised to read as follows:
Subpart B--Procedures for Testing Performance Characteristics of
Automated Methods for SO2, CO, O3, and NO2
Sec.
53.20 General provisions.
53.21 Test conditions.
53.22 Generation of test atmospheres.
53.23 Test procedure.
Figure B-1 to Subpart B of Part 53--Example
Table B-1 to Subpart B of Part 53--Performance Limit Specifications
for Automated Methods
Table B-2 to Subpart B of Part 53--Test Atmospheres
Table B-3 to Subpart B of Part 53--Interferent Test Concentration, 1
Parts Per Million
Table B-4 to Subpart B of Part 53-- Line Voltage and Room
Temperature Test Conditions
Table B-5 to Subpart B of Part 53--Symbols and Abbreviations
Appendix A to Subpart B--Optional Forms for Reporting Test Results
Subpart B--Procedures for Testing Performance Characteristics of
Automated Methods for SO2, CO, O3, and NO2
Sec. 53.20 General provisions.
(a) The test procedures given in this subpart shall be used to test
the performance of candidate automated methods against the performance
requirement specifications given in table B-1 to subpart B of part 53.
A test analyzer representative of the candidate automated method must
exhibit performance better than, or not outside, the specified limit or
limits for each such performance parameter specified (except range) to
satisfy the requirements of this subpart. Except as provided in
paragraph (b) of this section, the measurement range of the candidate
method must be the standard range specified in table B-1 to subpart B
of part 53 to satisfy the requirements of this subpart.
(b) Measurement ranges. For a candidate method having more than one
selectable measurement range, one range must be the standard range
specified in table B-1 to subpart B of part 53, and a test analyzer
representative of the method must pass the tests required by this
subpart while operated in that range.
(i) Higher ranges. The tests may be repeated for one or more higher
(broader) ranges (i.e., ranges extending to higher concentrations) than
the standard range specified in table B-1 to subpart B of part 53,
provided that the range does not extend to concentrations more than
four times the upper range limit of the standard range specified in
table B-1 to subpart B of part 53. For such higher ranges, only the
tests for range (calibration), noise at 80% of the upper range limit,
and lag, rise and fall time are required to be repeated. For the
purpose of testing a higher range, the test procedure of Sec. 53.23(e)
may be abridged to include only those components needed to test lag,
rise and fall time.
(ii) Lower ranges. The tests may be repeated for one or more lower
(narrower) ranges (i.e., ones extending to lower concentrations) than
the standard range specified in table B-1 to subpart B of part 53. For
methods for some pollutants, table B-1 to subpart B of part 53
specifies special performance limit requirements for lower ranges. If
special low-range performance limit requirements are not specified in
table B-1 to subpart B of part 53, then the performance limit
requirements for the standard range apply. For lower ranges for any
method, only the tests for range (calibration), noise at 0% of the
[[Page 54327]]
measurement range, lower detectable limit, (and nitric oxide
interference for SO2 UVF methods) are required to be
repeated, provided the tests for the standard range shows the
applicable limit specifications are met for the other test parameters.
(iii) If the tests are conducted and passed only for the specified
standard range, any FRM or FEM determination with respect to the method
will be limited to that range. If the tests are passed for both the
specified range and one or more higher or lower ranges, any such
determination will include the additional higher or lower range(s) as
well as the specified standard range. Appropriate test data shall be
submitted for each range sought to be included in a FRM or FEM method
determination under this paragraph (b).
(c) For each performance parameter (except range), the test
procedure shall be initially repeated seven (7) times to yield 7 test
results. Each result shall be compared with the corresponding
performance limit specification in table B-1 to subpart B of part 53; a
value higher than or outside the specified limit or limits constitutes
a failure. These 7 results for each parameter shall be interpreted as
follows:
(1) Zero (0) failures: The candidate method passes the test for the
performance parameter.
(2) Three (3) or more failures: The candidate method fails the test
for the performance parameter.
(3) One (1) or two (2) failures: Repeat the test procedures for the
performance parameter eight (8) additional times yielding a total of
fifteen (15) test results. The combined total of 15 test results shall
then be interpreted as follows:
(i) One (1) or two (2) failures: The candidate method passes the
test for the performance parameter.
(ii) Three (3) or more failures: The candidate method fails the
test for the performance parameter.
(d) The tests for zero drift, span drift, lag time, rise time, fall
time, and precision shall be carried out in a single integrated
procedure conducted at various line voltages and ambient temperatures
specified in Sec. 53.23(e). A temperature-controlled environmental
test chamber large enough to contain the test analyzer is recommended
for this test. The tests for noise, lower detectable limit, and
interference equivalent shall be conducted at any ambient temperature
between 20 [deg]C and 30 [deg]C, at any normal line voltage between 105
and 125 volts, and shall be conducted such that not more than three (3)
test results for each parameter are obtained in any 24-hour period.
(e) If necessary, all measurement response readings to be recorded
shall be converted to concentration units or adjusted according to the
calibration curve constructed in accordance with Sec. 53.21(b).
(f) All recorder chart tracings (or equivalent data plots),
records, test data and other documentation obtained from or pertinent
to these tests shall be identified, dated, signed by the analyst
performing the test, and submitted.
Note to Sec. 53.20: Suggested formats for reporting the test
results and calculations are provided in Figures B-2, B-3, B-4, B-5,
and B-6 in appendix A to this subpart. Symbols and abbreviations
used in this subpart are listed in table B-5 of appendix A to this
subpart.
Sec. 53.21 Test conditions.
(a) Set-up and start-up of the test analyzer shall be in strict
accordance with the operating instructions specified in the manual
referred to in Sec. 53.4(b)(3). Allow adequate warm-up or
stabilization time as indicated in the operating instructions before
beginning the tests. The test procedures assume that the test analyzer
has a conventional analog measurement signal output that is connected
to a suitable strip chart recorder of the servo, null-balance type.
This recorder shall have a chart width of at least 25 centimeters,
chart speeds up to 10 cm per hour, a response time of 1 second or less,
a deadband of not more than 0.25 percent of full scale, and capability
either of reading measurements at least 5 percent below zero or of
offsetting the zero by at least 5 percent. If the test analyzer does
not have an analog signal output, or if a digital or other type of
measurement data output is used for the tests, an alternative
measurement data recording device (or devices) may be used for
recording the test data, provided that the device is reasonably suited
to the nature and purposes of the tests, and an analog representation
of the analyzer measurements for each test can be plotted or otherwise
generated that is reasonably similar to the analog measurement
recordings that would be produced by a conventional chart recorder
connected to a conventional analog signal output.
(b) Calibration of the test analyzer shall be carried out prior to
conducting the tests described in this subpart. The calibration shall
be as indicated in the manual referred to in Sec. 53.4(b)(3) and as
follows: If the chart recorder or alternative data recorder does not
have below zero capability, adjust either the controls of the test
analyzer or the chart or data recorder to obtain a +5% offset zero
reading on the recorder chart to facilitate observing negative response
or drift. If the candidate method is not capable of negative response,
the test analyzer (not the data recorder) shall be operated with a
similar offset zero. Construct and submit a calibration curve showing a
plot of recorder scale readings or other measurement output readings
(vertical or y-axis) against pollutant concentrations presented to the
analyzer for measurement (horizontal or x-axis). If applicable, a plot
of base analog output units (volts, millivolts, milliamps, etc.)
against pollutant concentrations shall also be obtained and submitted.
All such calibration plots shall consist of at least seven (7)
approximately equally spaced, identifiable points, including 0 and 90
5 percent of the upper range limit (URL).
(c) Once the test analyzer has been set up and calibrated and the
tests started, manual adjustment or normal periodic maintenance is
permitted only every 3 days. Automatic adjustments which the test
analyzer performs by itself are permitted at any time. The submitted
records shall show clearly when any manual adjustment or periodic
maintenance was made during the tests and describe the specific
operations performed.
(d) If the test analyzer should malfunction during any of the
performance tests, the tests for that parameter shall be repeated. A
detailed explanation of the malfunction, remedial action taken, and
whether recalibration was necessary (along with all pertinent records
and charts) shall be submitted. If more than one malfunction occurs,
all performance test procedures for all parameters shall be repeated.
(e) Tests for all performance parameters shall be completed on the
same test analyzer; however, use of multiple test analyzers to
accelerate testing is permissible for testing additional ranges of a
multi-range candidate method.
Sec. 53.22 Generation of test atmospheres.
(a) Table B-2 to subpart B of part 53 specifies preferred methods
for generating test atmospheres and suggested methods of verifying
their concentrations. Only one means of establishing the concentration
of a test atmosphere is normally required, provided that that means is
adequately accurate and credible. If the method of generation can
produce accurate, reproducible concentrations, verification is
optional. If the method of generation is not reproducible or reasonably
quantifiable, then establishment of the concentration by
[[Page 54328]]
some credible verification method is required.
(b) The test atmosphere delivery system shall be designed and
constructed so as not to significantly alter the test atmosphere
composition or concentration during the period of the test. The system
shall be vented to insure that test atmospheres are presented to the
test analyzer at very nearly atmospheric pressure. The delivery system
shall be fabricated from borosilicate glass, FEP Teflon, or other
material that is inert with regard to the gas or gases to be used.
(c) The output of the test atmosphere generation system shall be
sufficiently stable to obtain stable response readings from the test
analyzer during the required tests. If a permeation device is used for
generation of a test atmosphere, the device, as well as the air passing
over it, shall be controlled to 0.1 [deg]C.
(d) All diluent air shall be zero air free of contaminants likely
to react with the test atmospheres or cause a detectable response on
the test analyzer.
(e) The concentration of each test atmosphere used shall be
quantitatively established and/or verified before or during each series
of tests. Samples for verifying test concentrations shall be collected
from the test atmosphere delivery system as close as feasible to the
sample intake port of the test analyzer.
(f) The accuracy of all flow measurements used to calculate test
atmosphere concentrations shall be documented and referenced to a
primary flow rate or volume standard (such as a spirometer, bubble
meter, etc.). Any corrections shall be clearly shown. All flow
measurements given in volume units shall be standardized to 25 [deg]C
and 760 mm Hg.
(g) Schematic drawings, photos, descriptions, and other information
showing complete procedural details of the test atmosphere generation,
verification, and delivery system shall be provided. All pertinent
calculations shall be clearly indicated.
Sec. 53.23 Test procedures.
(a) Range--(1) Technical definition. The nominal minimum and
maximum concentrations that a method is capable of measuring.
Note to Sec. 53.23(a)(1): The nominal range is given as the
lower and upper range limits in concentration units, for example, 0-
0.5 parts per million (ppm).
(2) Test procedure. Determine and submit a suitable calibration
curve, as specified in Sec. 53.21(b), showing the test analyzer's
measurement response over at least 95 percent of the required or
indicated measurement range.
Note to Sec. 53.23(a)(2): A single calibration curve for each
measurement range for which an FRM or FEM designation is sought will
normally suffice.
(b) Noise--(1) Technical definition. Spontaneous, short duration
deviations in measurements or measurement signal output, about the mean
output, that are not caused by input concentration changes. Measurement
noise is determined as the standard deviation of a series of
measurements of a constant concentration about the mean and is
expressed in concentration units.
(2) Test procedure. (i) Allow sufficient time for the test analyzer
to warm up and stabilize. Determine measurement noise at each of two
fixed concentrations, first using zero air and then a pollutant test
gas concentration as indicated below. The noise limit specification in
table B-1 to subpart B of part 53 shall apply to both of these tests.
(ii) For an analyzer with an analog signal output, connect an
integrating-type digital meter (DM) suitable for the test analyzer's
output and accurate to three significant digits, to determine the
analyzer's measurement output signal.
Note to Sec. 53.23(b)(2): Use of a chart recorder in addition
to the DM is optional.
(iii) Measure zero air with the test analyzer for 60 minutes.
During this 60-minute interval, record twenty-five (25) test analyzer
concentration measurements or DM readings at 2-minute intervals. (See
Figure B-2 in appendix A of this subpart.)
(iv) If applicable, convert each DM test reading to concentration
units (ppm) or adjust the test readings (if necessary) by reference to
the test analyzer's calibration curve as determined in Sec. 53.21(b).
Label and record the test measurements or converted DM readings as
r1, r2, r3 . . . ri . . .
r25.
(v) Calculate measurement noise as the standard deviation, S, as
follows:
[GRAPHIC] [TIFF OMITTED] TR31AU11.005
Where i indicates the i-th test measurement or DM reading in ppm.
(vi) Let S at 0 ppm be identified as S0; compare
S0 to the noise limit specification given in table B-1 to
subpart B of part 53.
(vii) Repeat steps in Paragraphs (b)(2)(iii) through (v) of this
section using a pollutant test atmosphere concentration of 80 5 percent of the URL instead of zero air, and let S at 80
percent of the URL be identified as S80. Compare
S80 to the noise limit specification given in table B-1 to
subpart B of part 53.
(viii) Both S0 and S80 must be less than or
equal to the table B-1 to subpart B of part 53 noise limit
specification to pass the test for the noise parameter.
(c) Lower detectable limit--(1) Technical definition. The minimum
pollutant concentration that produces a measurement or measurement
output signal of at least twice the noise level.
(2) Test procedure. (i) Allow sufficient time for the test analyzer
to warm up and stabilize. Measure zero air and record the stable
measurement reading in ppm as BZ. (See Figure B-3 in
appendix A of this subpart.)
(ii) Generate and measure a pollutant test concentration equal to
the value for the lower detectable limit specified in table B-1 to
subpart B of part 53.
Note to Sec. 53.23(c)(2): If necessary, the test concentration
may be generated or verified at a higher concentration, then
quantitatively and accurately diluted with zero air to the final
required test concentration.
(iii) Record the test analyzer's stable measurement reading, in
ppm, as BL.
(iv) Determine the lower detectable limit (LDL) test result as LDL
= BL - BZ. Compare this LDL value with the noise level, S0,
determined in Sec. 53.23(b), for the 0 concentration test atmosphere.
LDL must be equal to or higher than 2 x S0 to pass this
test.
(d) Interference equivalent--(1) Technical definition. Positive or
negative measurement response caused by a substance other than the one
being measured.
(2) Test procedure. The test analyzer shall be tested for all
substances likely to cause a detectable response. The test analyzer
shall be challenged, in turn, with each potential interfering agent
(interferent) specified in table B-3 to subpart B of part 53. In the
event that there are substances likely to cause a significant
interference which have not been specified in table B-3 to subpart B of
part 53, these substances shall also be tested, in a manner similar to
that for the specified interferents, at a concentration substantially
higher than that likely to be found in the ambient air. The
interference may be either positive or negative, depending on whether
the test analyzer's measurement response is increased or decreased by
the presence of the interferent. Interference equivalents shall be
determined by mixing each interferent, one at a time, with the
pollutant at an interferent test concentration not lower than the test
concentration specified in table B-3 to subpart B of part 53 (or as
otherwise required for unlisted interferents), and
[[Page 54329]]
comparing the test analyzer's measurement response to the response
caused by the pollutant alone. Known gas-phase reactions that might
occur between a listed interferent and the pollutant are designated by
footnote 3 in table B-3 to subpart B of part 53. In these cases, the
interference equivalent shall be determined without mixing with the
pollutant.
(i) Allow sufficient time for warm-up and stabilization of the test
analyzer.
(ii) For a candidate method using a prefilter or scrubber device
based upon a chemical reaction to derive part of its specificity and
which device requires periodic service or maintenance, the test
analyzer shall be ``conditioned'' prior to conducting each interference
test series. This requirement includes conditioning for the
NO2 converter in chemiluminescence NO/NO2/
NOX analyzers and for the ozone scrubber in UV-absorption
ozone analyzers. Conditioning is as follows:
(A) Service or perform the indicated maintenance on the scrubber or
prefilter device, as if it were due for such maintenance, as directed
in the manual referred to in Sec. 53.4(b)(3).
(B) Before testing for each potential interferent, allow the test
analyzer to sample through the prefilter or scrubber device a test
atmosphere containing the interferent at a concentration not lower than
the value specified in table B-3 to subpart B of part 53 (or, for
unlisted potential interferents, at a concentration substantially
higher than likely to be found in ambient air). Sampling shall be at
the normal flow rate and shall be continued for 6 continuous hours
prior to the interference test series. Conditioning for all applicable
interferents prior to any of the interference tests is permissible.
Also permissible is simultaneous conditioning with multiple
interferents, provided no interferent reactions are likely to occur in
the conditioning system.
(iii) Generate three test atmosphere streams as follows:
(A) Test atmosphere P: Pollutant test concentration.
(B) Test atmosphere I: Interferent test concentration.
(C) Test atmosphere Z: Zero air.
(iv) Adjust the individual flow rates and the pollutant or
interferent generators for the three test atmospheres as follows:
(A) The flow rates of test atmospheres I and Z shall be equal.
(B) The concentration of the pollutant in test atmosphere P shall
be adjusted such that when P is mixed (diluted) with either test
atmosphere I or Z, the resulting concentration of pollutant shall be as
specified in table B-3 to subpart B of part 53.
(C) The concentration of the interferent in test atmosphere I shall
be adjusted such that when I is mixed (diluted) with test atmosphere P,
the resulting concentration of interferent shall be not less than the
value specified in table B-3 to subpart B of part 53 (or as otherwise
required for unlisted potential interferents).
(D) To minimize concentration errors due to flow rate differences
between I and Z, it is recommended that, when possible, the flow rate
of P be from 10 to 20 times larger than the flow rates of I and Z.
(v) Mix test atmospheres P and Z by passing the total flow of both
atmospheres through a (passive) mixing component to insure complete
mixing of the gases.
(vi) Sample and measure the mixture of test atmospheres P and Z
with the test analyzer. Allow for a stable measurement reading, and
record the reading, in concentration units, as R (see Figure B-3).
(vii) Mix test atmospheres P and I by passing the total flow of
both atmospheres through a (passive) mixing component to insure
complete mixing of the gases.
(viii) Sample and measure this mixture of P and I with the test
analyzer. Record the stable measurement reading, in concentration
units, as RI.
(ix) Calculate the interference equivalent (IE) test result as:
IE = RI - R.
IE must be within the limits (inclusive) specified in table B-1 to
subpart B of part 53 for each interferent tested to pass the
interference equivalent test.
(x) Follow steps (iii) through (ix) of this section, in turn, to
determine the interference equivalent for each listed interferent as
well as for any other potential interferents identified.
(xi) For those potential interferents which cannot be mixed with
the pollutant, as indicated by footnote (3) in table B-3 to subpart B
of part 53, adjust the concentration of test atmosphere I to the
specified value without being mixed or diluted by the pollutant test
atmosphere. Determine IE as follows:
(A) Sample and measure test atmosphere Z (zero air). Allow for a
stable measurement reading and record the reading, in concentration
units, as R.
(B) Sample and measure the interferent test atmosphere I. If the
test analyzer is not capable of negative readings, adjust the analyzer
(not the recorder) to give an offset zero. Record the stable reading in
concentration units as RI, extrapolating the calibration curve, if
necessary, to represent negative readings.
(C) Calculate IE = RI - R. IE must be within the limits (inclusive)
specified in table B-1 to subpart B of part 53 for each interferent
tested to pass the interference equivalent test.
(xii) Sum the absolute value of all the individual interference
equivalent test results. This sum must be equal to or less than the
total interferent limit given in table B-1 to subpart B of part 53 to
pass the test.
(e) Zero drift, span drift, lag time, rise time, fall time, and
precision--(1) Technical definitions--(i) Zero drift: The change in
measurement response to zero pollutant concentration over 12- and 24-
hour periods of continuous unadjusted operation.
(ii) Span drift: The percent change in measurement response to an
up-scale pollutant concentration over a 24-hour period of continuous
unadjusted operation.
(iii) Lag time: The time interval between a step change in input
concentration and the first observable corresponding change in
measurement response.
(iv) Rise time: The time interval between initial measurement
response and 95 percent of final response after a step increase in
input concentration.
(v) Fall time: The time interval between initial measurement
response and 95 percent of final response after a step decrease in
input concentration.
(vi) Precision: Variation about the mean of repeated measurements
of the same pollutant concentration, expressed as one standard
deviation.
(2) Tests for these performance parameters shall be accomplished
over a period of seven (7) or fifteen (15) test days. During this time,
the line voltage supplied to the test analyzer and the ambient
temperature surrounding the analyzer shall be changed from day to day,
as required in paragraph (e)(4) of this section. One test result for
each performance parameter shall be obtained each test day, for seven
(7) or fifteen (15) test days, as determined from the test results of
the first seven days. The tests for each test day are performed in a
single integrated procedure.
(3) The 24-hour test day may begin at any clock hour. The first
approximately 12 hours of each test day are required for testing 12-
hour zero drift. Tests for the other parameters shall be conducted any
time during the remaining 12 hours.
(4) Table B-4 to subpart B of part 53 specifies the line voltage
and room temperature to be used for each test day. The applicant may
elect to specify a
[[Page 54330]]
wider temperature range (minimum and maximum temperatures) than the
range specified in table B-4 to subpart B of part 53 and to conduct
these tests over that wider temperature range in lieu of the specified
temperature range. If the test results show that all test parameters of
this section Sec. 53.23(e) are passed over this wider temperature
range, a subsequent FRM or FEM designation for the candidate method
based in part on this test shall indicate approval for operation of the
method over such wider temperature range. The line voltage and
temperature shall be changed to the specified values (or to the
alternative, wider temperature values, if applicable) at the start of
each test day (i.e., at the start of the 12-hour zero test). Initial
adjustments (day zero) shall be made at a line voltage of 115 volts
(rms) and a room temperature of 25 [deg]C.
(5) The tests shall be conducted in blocks consisting of 3 test
days each until 7 (or 15, if necessary) test results have been
obtained. (The final block may contain fewer than three test days.)
Test days need not be contiguous days, but during any idle time between
tests or test days, the test analyzer must operate continuously and
measurements must be recorded continuously at a low chart speed (or
equivalent data recording) and included with the test data. If a test
is interrupted by an occurrence other than a malfunction of the test
analyzer, only the block during which the interruption occurred shall
be repeated.
(6) During each test block, manual adjustments to the electronics,
gas, or reagent flows or periodic maintenance shall not be permitted.
Automatic adjustments that the test analyzer performs by itself are
permitted at any time.
(7) At least 4 hours prior to the start of the first test day of
each test block, the test analyzer may be adjusted and/or serviced
according to the periodic maintenance procedures specified in the
manual referred to in Sec. 53.4(b)(3). If a new block is to
immediately follow a previous block, such adjustments or servicing may
be done immediately after completion of the day's tests for the last
day of the previous block and at the voltage and temperature specified
for that day, but only on test days 3, 6, 9, and 12.
Note to Sec. 53.23(e)(7): If necessary, the beginning of the
test days succeeding such maintenance or adjustment may be delayed
as required to complete the service or adjustment operation.
(8) All measurement response readings to be recorded shall be
converted to concentration units or adjusted (if necessary) according
to the calibration curve. Whenever a test atmosphere is to be measured
but a stable reading is not required, the test atmosphere shall be
sampled and measured long enough to cause a change in measurement
response of at least 10% of full scale. Identify all readings and other
pertinent data on the strip chart (or equivalent test data record).
(See Figure B-1 to subpart B of part 53 illustrating the pattern of the
required readings.)
(9) Test procedure. (i) Arrange to generate pollutant test
atmospheres as follows. Test atmospheres A0, A20,
and A80 shall be maintained consistent during the tests and
reproducible from test day to test day.
------------------------------------------------------------------------
Pollutant concentration
Test atmosphere (percent)
------------------------------------------------------------------------
A0........................................ Zero air.
A20....................................... 20 5 of the
upper range limit.
A30....................................... 30 5 of the
upper range limit.
A80....................................... 80 5 of the
upper range limit.
A90....................................... 90 5 of the
upper range limit.
------------------------------------------------------------------------
(ii) For steps within paragraphs (e)(9)(xxv) through (e)(9)(xxxi)
of this section, a chart speed of at least 10 centimeters per hour (or
equivalent resolution for a digital representation) shall be used to
clearly show changes in measurement responses. The actual chart speed,
chart speed changes, and time checks shall be clearly marked on the
chart.
(iii) Test day 0. Allow sufficient time for the test analyzer to
warm up and stabilize at a line voltage of 115 volts and a room
temperature of 25 [deg]C. Adjust the zero baseline to 5 percent of
chart (see Sec. 53.21(b)) and recalibrate, if necessary. No further
adjustments shall be made to the analyzer until the end of the tests on
the third, sixth, ninth, or twelfth test day.
(iv) Measure test atmosphere A0 until a stable
measurement reading is obtained and record this reading (in ppm) as
Z'n, where n = 0 (see Figure B-4 in appendix A of this subpart).
(v) [Reserved.]
(vi) Measure test atmosphere A80. Allow for a stable
measurement reading and record it as S'n, where n = 0.
(vii) The above readings for Z'0 and S'0
should be taken at least four (4) hours prior to the beginning of test
day 1.
(viii) At the beginning of each test day, adjust the line voltage
and room temperature to the values given in table B-4 to subpart B of
part 53 (or to the corresponding alternative temperature if a wider
temperature range is being tested).
(ix) Measure test atmosphere A0 continuously for at
least twelve (12) continuous hours during each test day.
(x) After the 12-hour zero drift test (step ix) is complete, sample
test atmosphere A0. A stable reading is not required.
(xi) Measure test atmosphere A20 and record the stable
reading (in ppm) as P1. (See Figure B-4 in appendix A.)
(xii) Sample test atmosphere A30; a stable reading is
not required.
(xiii) Measure test atmosphere A20 and record the stable
reading as P2.
(xiv) Sample test atmosphere A0; a stable reading is not
required.
(xv) Measure test atmosphere A20 and record the stable
reading as P3.
(xvi) Sample test atmosphere A30; a stable reading is
not required.
(xvii) Measure test atmosphere A20 and record the stable
reading as P4.
(xviii) Sample test atmosphere A0; a stable reading is
not required.
(xix) Measure test atmosphere A20 and record the stable
reading as P5.
(xx) Sample test atmosphere A30; a stable reading is not
required.
(xxi) Measure test atmosphere A20 and record the stable
reading as P6.
(xxii) Measure test atmosphere A80 and record the stable
reading as P7.
(xxiii) Sample test atmosphere A90; a stable reading is
not required.
(xxiv) Measure test atmosphere A80 and record the stable
reading as P8. Increase the chart speed to at least 10
centimeters per hour.
(xxv) Measure test atmosphere A0. Record the stable
reading as L1.
(xxvi) Quickly switch the test analyzer to measure test atmosphere
A80 and mark the recorder chart to show, or otherwise
record, the exact time when the switch occurred.
(xxvii) Measure test atmosphere A80 and record the
stable reading as P9.
(xxviii) Sample test atmosphere A90; a stable reading is
not required.
(xxix) Measure test atmosphere A80 and record the stable
reading as P10.
(xxx) Measure test atmosphere A0 and record the stable
reading as L2.
(xxxi) Measure test atmosphere A80 and record the stable
reading as P11.
(xxxii) Sample test atmosphere A90; a stable reading is
not required.
(xxxiii) Measure test atmosphere A80 and record the
stable reading as P12.
(xxxiv) Repeat steps within paragraphs (e)(9)(viii) through
(e)(9)(xxxiii) of this section, each test day.
(xxxv) If zero and span adjustments are made after the readings are
taken on
[[Page 54331]]
test days 3, 6, 9, or 12, complete all adjustments; then measure test
atmospheres A0 and A80. Allow for a stable
reading on each, and record the readings as Z'n and S'n, respectively,
where n = the test day number (3, 6, 9, or 12). These readings must be
made at least 4 hours prior to the start of the next test day.
(10) Determine the results of each day's tests as follows. Mark the
recorder chart to show readings and determinations.
(i) Zero drift. (A) Determine the 12-hour zero drift by examining
the strip chart pertaining to the 12-hour continuous zero air test.
Determine the minimum (Cmin.) and maximum (Cmax.) measurement readings
(in ppm) during this period of 12 consecutive hours, extrapolating the
calibration curve to negative concentration units if necessary.
Calculate the 12-hour zero drift (12ZD) as 12ZD = Cmax. - Cmin. (See
Figure B-5 in appendix A.)
(B) Calculate the 24-hour zero drift (24ZD) for the n-th test day
as 24ZDn = Zn - Zn-1, or 24ZDn = Zn - Z'n-1 if zero adjustment was made
on the previous test day, where Zn = \1/2\(L1+L2)
for L1 and L2 taken on the n-th test day.
(C) Compare 12ZD and 24ZD to the zero drift limit specifications in
table B-1 to subpart B of part 53. Both 12ZD and 24ZD must be within
the specified limits (inclusive) to pass the test for zero drift.
(ii) Span drift.
(A) Calculate the span drift (SD) as:
[GRAPHIC] [TIFF OMITTED] TR31AU11.006
or if a span adjustment was made on the previous test day,
[GRAPHIC] [TIFF OMITTED] TR31AU11.007
where
[GRAPHIC] [TIFF OMITTED] TR31AU11.008
n indicates the n-th test day, and i indicates the i-th measurement
reading on the n-th test day.
(B) SD must be within the span drift limits (inclusive) specified
in table B-1 to subpart B of part 53 to pass the test for span drift.
(iii) Lag time. Determine, from the strip chart (or alternative
test data record), the elapsed time in minutes between the change in
test concentration (or mark) made in step (xxvi) and the first
observable (two times the noise level) measurement response. This time
must be equal to or less than the lag time limit specified in table B-1
to subpart B of part 53 to pass the test for lag time.
(iv) Rise time. Calculate 95 percent of measurement reading
P9 and determine, from the recorder chart (or alternative
test data record), the elapsed time between the first observable (two
times noise level) measurement response and a response equal to 95
percent of the P9 reading. This time must be equal to or
less than the rise time limit specified in table B-1 to subpart B of
part 53 to pass the test for rise time.
(v) Fall time. Calculate five percent of (P10 -
L2) and determine, from the strip chart (or alternative test
record), the elapsed time in minutes between the first observable
decrease in measurement response following reading P10 and a
response equal to L2 + five percent of (P10 -
L2). This time must be equal to or less than the fall time
limit specification in table B-1 to subpart B of part 53 to pass the
test for fall time.
(vi) Precision. Calculate precision (both P20 and
P80) for each test day as follows:
(A)
[GRAPHIC] [TIFF OMITTED] TR31AU11.009
(B)
[GRAPHIC] [TIFF OMITTED] TR31AU11.010
(C) Both P20 and P80 must be equal to or less
than the precision limits specified in table B-1 to subpart B of part
53 to pass the test for precision.
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Figure B-1 to Subpart B of Part 53--Example
[GRAPHIC] [TIFF OMITTED] TR31AU11.011
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[GRAPHIC] [TIFF OMITTED] TR31AU11.012
BILLING CODE 6560-50-C
Table B-2 to Subpart B of Part 53--Test Atmospheres
------------------------------------------------------------------------
Test gas Generation Verification
------------------------------------------------------------------------
Ammonia..................... Permeation device. Indophenol method,
Similar to system reference 3.
described in
references 1 and 2.
Carbon dioxide.............. Cylinder of zero air Use NIST-certified
or nitrogen standards whenever
containing CO2 as possible. If NIST
required to obtain standards are not
the concentration available, obtain 2
specified in table standards from
B-3. independent sources
which agree within
2 percent, or
obtain one standard
and submit it to an
independent
laboratory for
analysis, which
must agree within 2
percent of the
supplier's nominal
analysis.
Carbon monoxide............. Cylinder of zero air Use an FRM CO
or nitrogen analyzer as
containing CO as described in
required to obtain reference 8.
the concentration
specified in table
B-3.
Ethane...................... Cylinder of zero air Gas chromatography,
or nitrogen ASTM D2820,
containing ethane reference 10. Use
as required to NIST-traceable
obtain the gaseous methane or
concentration propane standards
specified in table for calibration.
B-3.
Ethylene.................... Cylinder of pre- Do.
purified nitrogen
containing ethylene
as required to
obtain the
concentration
specified in table
B-3.
Hydrogen chloride........... Cylinder \1\ of pre- Collect samples in
purified nitrogen bubbler containing
containing distilled water and
approximately 100 analyze by the
ppm of gaseous HCl. mercuric
Dilute with zero thiocyanate method,
air to ASTM (D612), p. 29,
concentration reference 4.
specified in table
B-3.
Hydrogen sulfide............ Permeation device Tentative method of
system described in analysis for H2S
references 1 and 2. content of the
atmosphere, p. 426,
reference 5.
Methane..................... Cylinder of zero air Gas chromatography
containing methane ASTM D2820,
as required to reference 10. Use
obtain the NIST-traceable
concentration methane standards
specified in table for calibration.
B-3.
Nitric oxide................ Cylinder \1\ of pre- Gas phase titration
purified nitrogen as described in
containing reference 6,
approximately 100 section 7.1.
ppm NO. Dilute with
zero air to
required
concentration.
Nitrogen dioxide............ 1. Gas phase 1. Use an FRM NO2
titration as analyzer calibrated
described in with a
reference 6. gravimetrically
2. Permeation calibrated
device, similar to permeation device.
system described in 2. Use an FRM NO2
reference 6. analyzer calibrated
by gas-phase
titration as
described in
reference 6.
Ozone....................... Calibrated ozone Use an FEM ozone
generator as analyzer calibrated
described in as described in
reference 9. reference 9.
[[Page 54334]]
Sulfur dioxide.............. 1. Permeation device Use an SO2 FRM or
as described in FEM analyzer as
references 1 and 2. described in
2. Dynamic dilution reference 7.
of a cylinder
containing
approximately 100
ppm SO2 as
described in
Reference 7.
Water....................... Pass zero air Measure relative
through distilled humidity by means
water at a fixed of a dew-point
known temperature indicator,
between 20[deg] and calibrated
30 [deg]C such that electrolytic or
the air stream piezo electric
becomes saturated. hygrometer, or wet/
Dilute with zero dry bulb
air to thermometer.
concentration
specified in table
B-3.
Xylene...................... Cylinder of pre- Use NIST-certified
purified nitrogen standards whenever
containing 100 ppm possible. If NIST
xylene. Dilute with standards are not
zero air to available, obtain 2
concentration standards from
specified in table independent sources
B-3. which agree within
2 percent, or
obtain one standard
and submit it to an
independent
laboratory for
analysis, which
must agree within 2
percent of the
supplier's nominal
analysis.
Zero air.................... 1. Ambient air
purified by
appropriate
scrubbers or other
devices such that
it is free of
contaminants likely
to cause a
detectable response
on the analyzer.
2. Cylinder of
compressed zero air
certified by the
supplier or an
independent
laboratory to be
free of
contaminants likely
to cause a
detectable response
on the analyzer.
------------------------------------------------------------------------
\1\ Use stainless steel pressure regulator dedicated to the pollutant
measured.
Reference 1. O'Keefe, A. E., and Ortaman, G. C. ``Primary Standards for
Trace Gas Analysis,'' Anal. Chem. 38, 760 (1966).
Reference 2. Scaringelli, F. P., A. E. . Rosenberg, E*, and Bell, J. P.,
``Primary Standards for Trace Gas Analysis.'' Anal. Chem. 42, 871
(1970).
Reference 3. ``Tentative Method of Analysis for Ammonia in the
Atmosphere (Indophenol Method)'', Health Lab Sciences, vol. 10, No. 2,
115-118, April 1973.
Reference 4. 1973 Annual Book of ASTM Standards, American Society for
Testing and Materials, 1916 Race St., Philadelphia, PA.
Reference 5. Methods for Air Sampling and Analysis, Intersociety
Committee, 1972, American Public Health Association, 1015.
Reference 6. 40 CFR 50 Appendix F, ``Measurement Principle and
Calibration Principle for the Measurement of Nitrogen Dioxide in the
Atmosphere (Gas Phase Chemiluminescence).''
Reference 7. 40 CFR 50 Appendix A-1, ``Measurement Principle and
Calibration Procedure for the Measurement of Sulfur Dioxide in the
Atmosphere (Ultraviolet FIuorscence).''
Reference 8. 40 CFR 50 Appendix C, ``Measurement Principle and
Calibration Procedure for the Measurement of Carbon Monoxide in the
Atmosphere (Non-Dispersive Infrared Photometry)''.
Reference 9. 40 CFR 50 Appendix D, ``Measurement Principle and
Calibration Procedure for the Measurement of Ozone in the
Atmosphere''.
Reference 10. ``Standard Test Method for C, through C5 Hydrocarbons in
the Atmosphere by Gas Chromatography'', D 2820, 1987 Annual Book of
Aston Standards, vol 11.03, American Society for Testing and
Materials, 1916 Race St., Philadelphia, PA 19103.
[[Page 54335]]
Table B-3 to Subpart B of Part 53--Interferent Test Concentration,\1\ Parts per Million
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Hydro-
Pollutant Analyzer type chloric Ammonia Hydrogen Sulfur Nitrogen Nitric Carbon Ethylene Ozone Mxylene Water Carbon Methane Ethane Naphthalene
acid sulfide dioxide dioxide oxide dioxide vapor monoxide
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SO2............... Ultraviolet ........ ........ \5\ 0.1 \4\ 0.14 0.5 0.5 ........ ........ 0.5 0.2 20,000 ........ ........ ........ \6\ 0.05
fluorescence.
SO2............... Flame photometric.. ........ ........ 0.01 \4\ 0.14 ........ ........ 750 ........ ........ ........ \3\ 50 ........ ........ ...........
20,000
SO2............... Gas chromatography. ........ ........ 0.1 \4\ 0.14 ........ ........ 750 ........ ........ ........ \3\ 50 ........ ........ ...........
20,000
SO2............... Spectrophotometric- 0.2 0.1 0.1 \4\ 0.14 0.5 ........ 750 ........ 0.5 ........ ........ ........ ........ ........ ...........
wet chemical
(pararosanaline).
SO2............... Electrochemical.... 0.2 0.1 0.1 \4\ 0.14 0.5 0.5 ........ 0.2 0.5 ........ \3\ ........ ........ ........ ...........
20,000
SO2............... Conductivity....... 0.2 0.1 ........ \4\ 0.14 0.5 ........ 750 ........ ........ ........ ........ ........ ........ ........ ...........
SO2............... Spectrophotometric- ........ ........ ........ \4\ 0.14 0.5 ........ ........ ........ 0.5 0.2 ........ ........ ........ ........ ...........
gas phase,
including DOAS.
O3................ Chemiluminescent... ........ ........ \3\ 0.1 ........ ........ ........ 750 ........ \4\ 0.08 ........ \3\ ........ ........ ........ ...........
20,000
O3................ Electrochemical.... ........ \3\ 0.1 ........ 0.5 0.5 ........ ........ ........ \4\ 0.08 ........ ........ ........ ........ ........ ...........
O3................ Spectrophotometric- ........ \3\ 0.1 ........ 0.5 0.5 \3\ 0.5 ........ ........ \4\ 0.08 ........ ........ ........ ........ ........ ...........
wet chemical
(potassium iodide).
O3................ Spectrophotometric- ........ ........ ........ 0.5 0.5 0.5 ........ ........ \4\ 0.08 0.02 20,000 ........ ........ ........ ...........
gas phase,
including
ultraviolet
absorption and
DOAS).
CO................ Non-dispersive ........ ........ ........ ........ ........ ........ 750 ........ ........ ........ 20,000 \4\ 10 ........ ........ ...........
Infrared.
CO................ Gas chromatography ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ 20,000 \4\ 10 ........ 0.5 ...........
with flame
ionization
detector.
CO................ Electrochemical.... ........ ........ ........ ........ ........ 0.5 ........ 0.2 ........ ........ 20,000 \4\ 10 ........ ........ ...........
CO................ Catalytic ........ 0.1 ........ ........ ........ ........ 750 0.2 ........ ........ 20,000 \4\ 10 5.0 0.5 ...........
combustion-thermal
detection.
CO................ IR fluorescence.... ........ ........ ........ ........ ........ ........ 750 ........ ........ ........ 20,000 \4\ 10 ........ 0.5 ...........
CO................ Mercury replacement- ........ ........ ........ ........ ........ ........ ........ 0.2 ........ ........ ........ \4\ 10 ........ 0.5 ...........
UV photometric.
NO2............... Chemiluminescent... ........ \3\ 0.1 ........ 0.5 \4\ 0.1 0.5 ........ ........ ........ ........ 20,000 ........ ........ ........ ...........
NO2............... Spectrophotometric- ........ ........ ........ 0.5 \4\ 0.1 0.5 750 ........ 0.5 ........ ........ ........ ........ ........ ...........
wet chemical (azo-
dye reaction).
NO2............... Electrochemical.... 0.2 \3\ 0.1 ........ 0.5 \4\ 0.1 0.5 750 ........ 0.5 ........ 20,000 50 ........ ........ ...........
NO2............... Spectrophotometric- ........ \3\ 0.1 ........ 0.5 \4\ 0.1 0.5 ........ ........ 0.5 ........ 20,000 50 ........ ........ ...........
gas phase.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Concentrations of interferent listed must be prepared and controlled to 10 percent of the stated value.
\2\ Analyzer types not listed will be considered by the Administrator as special cases.
\3\ Do not mix with the pollutant.
\4\ Concentration of pollutant used for test. These pollutant concentrations must be prepared to 10 percent of the stated value.
\5\ If candidate method utilizes an elevated-temperature scrubber for removal of aromatic hydrocarbons, perform this interference test.
\6\ If naphthalene test concentration cannot be accurately quantified, remove the scrubber, use a test concentration that causes a full scale response, reattach the scrubber, and evaluate
response for interference.
[[Page 54336]]
Table B-4 to Subpart B of Part 53--Line Voltage and Room Temperature Test Conditions
----------------------------------------------------------------------------------------------------------------
Room
Test day Line temperature,\2\ Comments
voltage,\1\ rms [deg]C
----------------------------------------------------------------------------------------------------------------
0........................................ 115 25 Initial set-up and adjustments.
1........................................ 125 20 .................................
2........................................ 105 20 .................................
3........................................ 125 30 Adjustments and/or periodic
maintenance permitted at end of
tests.
4........................................ 105 30 .................................
5........................................ 125 20 .................................
6........................................ 105 20 Adjustments and/or periodic
maintenance permitted at end of
tests.
7........................................ 125 30 Examine test results to ascertain
if further testing is required.
8........................................ 105 30 .................................
9........................................ 125 20 Adjustments and/or periodic
maintenance permitted at end of
tests.
10....................................... 105 20 .................................
11....................................... 125 30 .................................
12....................................... 105 30 Adjustments and/or periodic
maintenance permitted at end of
tests.
13....................................... 125 20 .................................
14....................................... 105 20 .................................
15....................................... 125 30 .................................
----------------------------------------------------------------------------------------------------------------
\1\ Voltage specified shall be controlled to 1 volt.
\2\ Temperatures shall be controlled to 1 [deg]C.
Table B-5 to Subpart B of Part 53--Symbols and Abbreviations
BL--Analyzer reading at the specified LDL test concentration for the
LDL test.
BZ--analyzer reading at 0 concentration for the LDL test.
DM--Digital meter.
Cmax--Maximum analyzer reading during the 12ZD test period.
Cmin--Minimum analyzer reading during the 12ZD test period.
i--Subscript indicating the i-th quantity in a series.
IE--Interference equivalent.
L1--First analyzer zero reading for the 24ZD test.
L2--Second analyzer zero reading for the 24ZD test.
n--Subscript indicating the test day number.
P--Analyzer reading for the span drift and precision tests.
Pi--The i-th analyzer reading for the span drift and precision
tests.
P20--Precision at 20 percent of URL.
P80--Precision at 80 percent of URL.
ppb--Parts per billion of pollutant gas (usually in air), by volume.
ppm--Parts per million of pollutant gas (usually in air), by volume.
R--Analyzer reading of pollutant alone for the IE test.
R1--Analyzer reading with interferent added for the IE
test.
ri--the i-th analyzer or DM reading for the noise test.
S--Standard deviation of the noise test readings.
S0--Noise value (S) measured at 0 concentration.
S80--Noise value (S) measured at 80 percent of the URL.
Sn--Average of P7 . . . P12 for the n-th test
day of the SD test.
S'n--Adjusted span reading on the n-th test day.
SD--Span drift
URL--Upper range limit of the analyzer's measurement range.
Z--Average of L1 and L2 readings for the 24ZD
test.
Zn--Average of L1 and L2 readings on the n-th
test day for the 24ZD test.
Z'n--Adjusted analyzer zero reading on the n-the test day for the
24ZD test.
ZD--Zero drift.
12ZD--12-hour zero drift.
24ZD--24-hour zero drift.
Appendix A to Subpart B of Part 53--Optional Forms for Reporting Test
Results
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[GRAPHIC] [TIFF OMITTED] TR31AU11.014
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BILLING CODE 6560-50-C
PART 58--AMBIENT AIR QUALITY SURVEILLANCE
0
5. The authority citation for part 58 continues to read as follows:
Authority: 42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619.
Subpart B--[Amended]
0
6. Section 58.10, is amended by adding paragraph (a)(7) to read as
follows:
Sec. 58.10 Annual monitoring network plan and periodic network
assessment.
(a) * * *
(7) A plan for establishing CO monitoring sites in accordance with
the requirements of appendix D to this part shall be submitted to the
EPA Regional Administrator. Plans for required CO monitors shall be
submitted at least six months prior to the date such monitors must be
established as required by section 58.13.
* * * * *
0
7. Section 58.13 is amended by adding paragraph (e) to read as follows:
Sec. 58.13 Monitoring network completion.
* * * * *
(e) The CO monitors required under Appendix D, section 4.2 of this
part must be physically established and operating under all of the
requirements of this part, including the requirements of appendices A,
C, D, and E to this part, no later than:
(1) January 1, 2015 for CO monitors in CBSAs having 2.5 million
persons or more; or
(2) January 1, 2017 for other CO monitors.
[[Page 54342]]
0
8. Appendix D to Part 58 is amended by revising section 4.2 to read as
follows:
Appendix D to Part 58--Network Design Criteria for Ambient Air Quality
Monitoring
* * * * *
4.2 Carbon Monoxide (CO) Design Criteria
4.2.1 General Requirements. (a) Except as provided in subsection
(b), one CO monitor is required to operate collocated with one
required near-road NO2 monitor, as required in Section
4.3.2 of this part, in CBSAs having a population of 1,000,000 or
more persons. If a CBSA has more than one required near-road
NO2 monitor, only one CO monitor is required to be
collocated with a near-road NO2 monitor within that CBSA.
(b) If a state provides quantitative evidence demonstrating that
peak ambient CO concentrations would occur in a near-road location
which meets microscale siting criteria in Appendix E of this part
but is not a near-road NO2 monitoring site, then the EPA
Regional Administrator may approve a request by a state to use such
an alternate near-road location for a CO monitor in place of
collocating a monitor at near-road NO2 monitoring site.
4.2.2 Regional Administrator Required Monitoring. (a) The
Regional Administrators, in collaboration with states, may require
additional CO monitors above the minimum number of monitors required
in 4.2.1 of this part, where the minimum monitoring requirements are
not sufficient to meet monitoring objectives. The Regional
Administrator may require, at his/her discretion, additional
monitors in situations where data or other information suggest that
CO concentrations may be approaching or exceeding the NAAQS. Such
situations include, but are not limited to, (1) characterizing
impacts on ground-level concentrations due to stationary CO sources,
(2) characterizing CO concentrations in downtown areas or urban
street canyons, and (3) characterizing CO concentrations in areas
that are subject to high ground level CO concentrations particularly
due to or enhanced by topographical and meteorological impacts. The
Regional Administrator and the responsible State or local air
monitoring agency shall work together to design and maintain the
most appropriate CO network to address the data needs for an area,
and include all monitors under this provision in the annual
monitoring network plan.
4.2.3 CO Monitoring Spatial Scales. (a) Microscale and middle
scale measurements are the most useful site classifications for CO
monitoring sites since most people have the potential for exposure
on these scales. Carbon monoxide maxima occur primarily in areas
near major roadways and intersections with high traffic density and
often in areas with poor atmospheric ventilation.
(1) Microscale--Microscale measurements typically represent
areas in close proximity to major roadways, within street canyons,
over sidewalks, and in some cases, point and area sources. Emissions
on roadways result in high ground level CO concentrations at the
microscale, where concentration gradients generally exhibit a marked
decrease with increasing downwind distance from major roads, or
within downtown areas including urban street canyons. Emissions from
stationary point and area sources, and non-road sources may, under
certain plume conditions, result in high ground level concentrations
at the microscale.
(2) Middle scale--Middle scale measurements are intended to
represent areas with dimensions from 100 meters to 0.5 kilometer. In
certain cases, middle scale measurements may apply to areas that
have a total length of several kilometers, such as ``line'' emission
source areas. This type of emission sources areas would include air
quality along a commercially developed street or shopping plaza,
freeway corridors, parking lots and feeder streets.
(3) Neighborhood scale--Neighborhood scale measurements are
intended to represent areas with dimensions from 0.5 kilometers to 4
kilometers. Measurements of CO in this category would represent
conditions throughout some reasonably urban sub-regions. In some
cases, neighborhood scale data may represent not only the immediate
neighborhood spatial area, but also other similar such areas across
the larger urban area. Neighborhood scale measurements provide
relative area-wide concentration data which are useful for providing
relative urban background concentrations, supporting health and
scientific research, and for use in modeling.
* * * * *
0
9. Appendix E to Part 58 is amended by revising sections 2 and 6.2(a),
6.2(b), 6.2(c), and Table E-4 to read as follows:
Appendix E to Part 58--Probe and Monitoring Path Siting Criteria for
Ambient Air Quality Monitoring
* * * * *
2. Horizontal and Vertical Placement
The probe or at least 80 percent of the monitoring path must be
located between 2 and 15 meters above ground level for all
O3 and SO2 monitoring sites, and for
neighborhood or larger spatial scale Pb, PM10,
PM10-2.5, PM2.5, NO2, and CO sites.
Middle scale PM10-2.5 sites are required to have sampler
inlets between 2 and 7 meters above ground level. Microscale Pb,
PM10, PM10-2.5, and PM2.5 sites are
required to have sampler inlets between 2 and 7 meters above ground
level. Microscale near-road NO2 monitoring sites are
required to have sampler inlets between 2 and 7 meters above ground
level. The inlet probes for microscale carbon monoxide monitors that
are being used to measure concentrations near roadways must be
between 2 and 7 meters above ground level. Those inlet probes for
microscale carbon monoxide monitors measuring concentrations near
roadways in downtown areas or urban street canyons must be between
2.5 and 3.5 meters above ground level. The probe or at least 90
percent of the monitoring path must be at least 1 meter vertically
or horizontally away from any supporting structure, walls, parapets,
penthouses, etc., and away from dusty or dirty areas. If the probe
or a significant portion of the monitoring path is located near the
side of a building or wall, then it should be located on the
windward side of the building relative to the prevailing wind
direction during the season of highest concentration potential for
the pollutant being measured.
* * * * *
6. * * *
6.2 Spacing for Carbon Monoxide Probes and Monitoring Paths. (a)
Near-road microscale CO monitoring sites, including those located in
downtown areas, urban street canyons, and other near-road locations
such as those adjacent to highly trafficked roads, are intended to
provide a measurement of the influence of the immediate source on
the pollution exposure on the adjacent area.
(b) Microscale CO monitor inlets probes in downtown areas or
urban street canyon locations shall be located a minimum distance of
2 meters and a maximum distance of 10 meters from the edge of the
nearest traffic lane.
(c) Microscale CO monitor inlet probes in downtown areas or
urban street canyon locations shall be located at least 10 meters
from an intersection and preferably at a midblock location. Midblock
locations are preferable to intersection locations because
intersections represent a much smaller portion of downtown space
than do the streets between them. Pedestrian exposure is probably
also greater in street canyon/corridors than at intersections.
(d) Microscale CO monitor inlet probes in the near-road
environment, outside of downtown areas or urban street canyons,
shall be as near as practicable to the outside nearest edge of the
traffic lanes of the target road segment; but shall not be located
at a distance greater than 50 meters, in the horizontal, from the
outside nearest edge of the traffic lanes of the target road
segment.
(e) In determining the minimum separation between a neighborhood
scale monitoring site and a specific roadway, the presumption is
made that measurements should not be substantially influenced by any
one roadway. Computations were made to determine the separation
distance, and Table E-2 of this appendix provides the required
minimum separation distance between roadways and a probe or 90
percent of a monitoring path. Probes or monitoring paths that are
located closer to roads than this criterion allows should not be
classified as neighborhood scale, since the measurements from such a
site would closely represent the middle scale. Therefore, sites not
meeting this criterion should be classified as middle scale.
* * * * *
[[Page 54343]]
Table E-4 of Appendix E to Part 58--Summary of Probe and Monitoring Path Siting Criteria
--------------------------------------------------------------------------------------------------------------------------------------------------------
Horizontal and
vertical distance
Scale (maximum Height from ground to from supporting Distance from trees Distance from
Pollutant monitoring path probe, inlet or 80% of structures \2\ to to probe, inlet or roadways to probe,
length, meters) \1\ monitoring path \1\ probe, inlet or 90% 90% of monitoring inlet or monitoring
of monitoring path path \1\ (meters) path \1\ (meters)
\1\ (meters)
--------------------------------------------------------------------------------------------------------------------------------------------------------
SO2 \3\ \4\ \5\ \6\................ Middle (300 m) 2-15.................. > 1.................. > 10................. N/A.
Neighborhood Urban,
and Regional (1 km).
CO \4\ \5\ \7\..................... Micro [downtown or 2.5-3.5; 2-7; 2-15.... > 1.................. > 10................. 2-10 for downtown
street canyon sites], areas or street
micro [near-road canyon microscale;
sites], middle (300 50 for near-road
m) and Neighborhood microscale; see
(1 km). Table E-2 of this
appendix for middle
and neighborhood
scales.
O3 \3\ \4\ \5\..................... Middle (300 m) 2-15.................. > 1.................. > 10................. See Table E-1 of this
Neighborhood, Urban, appendix for all
and Regional (1 km). scales.
NO2 \3\ \4\ \5\.................... Micro (Near-road [50- 2-7 (micro); 2-15 (all > 1.................. > 10................. 50 meters for near-
300]) Middle (300m) other scales). road microscale;
Neighborhood, Urban, See Table E-1 of this
and Regional (1 km). appendix for all
other scales.
Ozone precursors (for PAMS) \3\ \4\ Neighborhood and Urban 2-15.................. > 1.................. > 10................. See Table E-4 of this
\5\. (1 km). appendix for all
scales.
PM, Pb 3 4 5 6 8................... Micro: Middle, 2-7 (micro); 2-7 > 2 (all scales, > 10 (all scales).... 2-10 (micro); see
Neighborhood, Urban (middle PM10 2.5); 2- horizontal distance Figure E-1 of this
and Regional. 15 (all other scales). only). appendix for all
other scales.
--------------------------------------------------------------------------------------------------------------------------------------------------------
N/A--Not applicable.
\1\ Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring, middle, neighborhood, urban, and regional
scale NO2 monitoring, and all applicable scales for monitoring SO2,O3, and O3 precursors.
\2\ When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses located on roof.
\3\ Should be > 20 meters from the drip-line of tree(s) and must be 10 meters from the drip-line when the tree(s) act as an obstruction.
\4\ Distance from sampler, probe, or 90% of monitoring path to obstacle, such as a building, must be at least twice the height the obstacle protrudes
above the sampler, probe, or monitoring path. Sites not meeting this criterion may be classified as middle scale (see text).
\5\ Must have unrestricted airflow 270 degrees around the probe or sampler; 180 degrees if the probe is on the side of a building or a wall.
\6\ The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration flues. The separation distance is
dependent on the height of the minor source's emission point (such as a flue), the type of fuel or waste burned, and the quality of the fuel (sulfur,
ash, or lead content). This criterion is designed to avoid undue influences from minor sources.
\7\ For microscale CO monitoring sites in downtown areas or street canyons (not at near-road NO2 monitoring sites), the probe must be > 10 meters from a
street intersection and preferably at a midblock location.
\8\ Collocated monitors must be within 4 meters of each other and at least 2 meters apart for flow rates greater than 200 liters/min or at least 1 meter
apart for samplers having flow rates less than 200 liters/min to preclude airflow interference.
* * * * *
[FR Doc. 2011-21359 Filed 8-30-11; 8:45 am]
BILLING CODE 6560-50-P