Mariposa County Breathes Easy: Ozone Standards Met
Published Date: 10/30/2025
Rule
Summary
Good news for Mariposa County, California! The EPA has confirmed that the area met the 2015 ozone air quality standards by the August 2024 deadline. This means no extra pollution control rules or penalties are needed, and the decision takes effect December 1, 2025.
Analyzed Economic Effects
3 provisions identified: 2 benefits, 1 costs, 0 mixed.
Mariposa Met 2015 Ozone Standard
The EPA determined that the Mariposa County area in California attained the 2015 8-hour ozone standard by the attainment date of August 3, 2024, based on complete, quality-assured, certified monitoring data for calendar years 2021–2023 (excluding exceedances from exceptional events). The EPA used the 0.070 parts per million (ppm) 3-year design value threshold, and the rule is effective December 1, 2025.
Contingency Measures No Longer Required
Because EPA determined attainment by the August 3, 2024 date, Clean Air 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 the Mariposa area for this standard. This change is effective December 1, 2025.
Mariposa Remains Moderate Nonattainment
Even though the area attained the 2015 ozone standard by August 3, 2024, the Mariposa area will not be redesignated and will continue to comply with requirements that apply to a Moderate ozone nonattainment area. This status and continuation of applicable Moderate-area requirements are effective December 1, 2025.
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