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Air Quality Improvement Planning

Yuma | Ozone Maintenance Area

Revised On: Apr. 1st, 2026 - 01:02 pm

County Affected:

Parts of Yuma County | View on a Map >

Pollutant of Concern:

2015 Ozone (O3) National Ambient Air Quality Standard (NAAQS)

Classification Level: 

Attainment/Maintenance

Nonattainment Area Designation and Reclassification Dates:

June 4, 2018 — Designation as Marginal Nonattainment for the 2015 O3 NAAQS | View 83 Federal Register 25786 >

Dec. 18, 2025 — Reclassification from Marginal Nonattainment to Attainment for the 2015 O3 NAAQS | View 90 Federal Register 51548 > 

Summary: 

On Nov. 18, 2025, the U.S. Environmental Protection Agency (EPA) approved  Arizona's Maintenance Plan and request to redesignate the Yuma area from nonattainment to attainment for the 2015 O3 NAAQS. This achievement transitions the area from its previous designation as Marginal nonattainment to attainment with respect to the 2015 O3 NAAQS.  

EPA’s approval confirms that the area has successfully attained the 2015 O3 NAAQS, implemented permanent and enforceable air quality control measures, developed a comprehensive 10-year maintenance plan, and met all Clean Air Act (CAA) requirements needed for redesignation | View 90 Federal Register 51548 >

A second 10-year maintenance plan for the area is due to EPA in 2033.

Regulatory Background:

In 2015, EPA revised the NAAQS for O3 by lowering the level of the standard from 75 parts per billion (ppb) (2008 O3 NAAQS) to 70 ppb (2015 O3 NAAQS). On June 4, 2018, the EPA designated Yuma as Marginal nonattainment for the 2015 O3 NAAQS | View 83 Federal Register 25785 >

Under CAA section 182(a), to improve the area's air quality and bring the area into compliance with the 2015 O3 NAAQS, Arizona was required to submit a State Implementation Plan (SIP) for the Yuma Nonattainment Area to the EPA. ADEQ submitted this SIP revision to EPA on Dec. 22, 2020. 

On Oct. 7, 2022, EPA determined that the Yuma area attained the 2015 O3 NAAQS by the marginal area attainment date of Aug. 3, 2021. EPA based its determination on ambient air quality data for the period of 2018-2020 | View 87 Federal Register 60898 >

EPA’s Clean Data Determination for the area suspended certain nonattainment area planning requirements for so long as the area continued to meet the NAAQS. Nonetheless, the area still had to meet additional CAA requirements in order to be redesignated from nonattainment to attainment. 

 For the purpose of demonstrating that the area had met all CAA requirements needed for redesignation and to fulfil other requirements of the CAA, ADEQ submitted a Redesignation Request and Maintenance Plan for the area to EPA in December 2023. As required by the CAA, the Yuma O3 Redesignation Request and Maintenance Plan included a demonstration that the area will continue to maintain the NAAQS for at least 10 years following redesignation, contingency measures to correct for any future violations of the NAAQS, and public process documentation. ADEQ worked collaboratively with permitted facilities, local state and federal government, and community stakeholders to develop the Redesignation Request and Maintenance Plan.

On Nov. 5, 2024, EPA proposed to approve ADEQ’s request to redesignate the Yuma nonattainment area and approve the SIP Revision: 2015 O3 NAAQS, Yuma Redesignation and Maintenance Plan | View 89 Federal Register 87828 >

On Nov. 18, 2025 (effective date: Dec. 18, 2025), EPA published a final rule formally approving Arizona's request to redesignate the Yuma area from nonattainment to attainment for the 2015 O3 NAAQS. This final rule fulfills all requirements for redesignation under CAA section 107(d)(3)(E), including the determination that the air quality improvement is due to permanent and enforceable emissions reductions. The area is now subject to the requirements of a Maintenance Area for the 2015 O3 NAAQS | View 90 Federal Register 51548 > 

Submitted SIPs for the Yuma O3 Area:

Learn more about O3 ground-level pollution | View Criteria Pollutants >

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