(a) The level of the national primary and secondary ambient air quality standards for ozone measured by a reference method based on appendix D to this part and designated in accordance with part 53 of this chapter, is 0.12 part per million (235 μg/m3). The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 part per million (235 μg/m3) is equal to or less than 1, as determined by appendix H.