Final rule · 2025-19714

Determination of Attainment by the Attainment Date; California; Mariposa County; 2015 8-Hour Ozone National Ambient Air Quality Standards

The Environmental Protection Agency (EPA) is taking final action to determine that the Mariposa County nonattainment area in California ("Mariposa area") attained the 2015 ozone national ambient air quality standards (NAAQS or "standard") by its August 3, 2024 attainment date. Our determination of attainment is based on complete, quality-assured, and certified ambient air quality monitoring data for calendar years 2021-2023, excluding data that showed exceedances due to exceptional events that occurred in 2021 and 2022. As a result of this action, Clean Air Act (CAA or "Act") section 172(c)(9) contingency measures for failure to attain the 2015 ozone NAAQS and contingency measures for failure to make reasonable further progress (RFP) are no longer required for this standard in the Mariposa area. This action fulfills the EPA's statutory obligation to determine whether the Mariposa area attained the NAAQS by the attainment date.