Code of Federal Regulations Title 40. Protection of Environment § 40.50.15 National primary and secondary ambient air quality standards for ozone

(a) The level of the national 8–hour primary and secondary ambient air quality standards for ozone (O₃) is 0.075 parts per million (ppm), daily maximum 8–hour average, measured by a reference method based on appendix D to this part and designated in accordance with part 53 of this chapter or an equivalent method designated in accordance with part 53 of this chapter.

(b) The 8–hour primary and secondary O₃ ambient air quality standards are met at an ambient air quality monitoring site when the 3–year average of the annual fourth-highest daily maximum 8–hour average O₃ concentration is less than or equal to 0.075 ppm, as determined in accordance with appendix P to this part.