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Air Quality Improvement Planning

Phoenix-Mesa | Ozone Nonattainment Area

Revised On: Jun. 26th, 2026 - 12:22 pm

Counties Affected:

Parts of Maricopa, Gila and Pinal County | View eMap >

Nonattainment Area Designation and Reclassification Dates:

Designation as nonattainment for the 2008 ozone National Ambient Air Quality Standards (NAAQS) with a marginal classification on July 20, 2012. Learn more about the designation of the area in the Federal Register (77 FR 30088) | View 2012 Designation >

Reclassification to a moderate nonattainment area for the 2008 ozone NAAQS on June 3, 2016. Learn more about the designation of the area in the Federal Register (81 FR 26697) | View 2016 Reclassification >

Designation as nonattainment for the revised 2015 ozone NAAQS with a marginal classification on Aug. 3, 2018. Learn more about the designation of the area in the Federal Register (83 FR 25776) | View 2018 Designation >

Reclassification to a moderate nonattainment area for the revised 2015 ozone NAAQS on Nov. 7, 2022. Learn more about the designation of the area in the Federal Register (87 FR 60897) | View 2022 Reclassification >

Current Classification Level: 

  • Moderate classification under the 2008 ozone NAAQS. 
  • Moderate classification under the 2015 ozone NAAQS.

Pollutants of Concern:

  • Ozone (O3)
  • Precursor Pollutants:
    • Volatile Organic Compounds (VOCs)
    • Nitrogen Oxides (NOx)

Ozone is an invisible irritant that occurs both high in the atmosphere and at ground level. In the stratosphere, about 10 to 19 miles above Earth, ozone forms a protective layer that shields life from harmful ultraviolet (UV) rays. Near the surface, however, ozone becomes a pollutant formed when sunlight triggers chemical reactions between VOCs and NOx.

Within the Phoenix-Mesa Ozone Nonattainment Area, ground-level ozone concentrations tend to be higher during warm, sunny weather, especially in summer. In addition to local pollution sources, ozone can also reach the surface through stratospheric ozone intrusions, which are natural events where ozone from the upper atmosphere descends to ground level. Wildfires are another growing contributor, releasing large amounts of VOCs and NOx that fuel ozone formation. Elevated ozone levels are particularly harmful to at-risk groups including children, older adults, people of all ages who have lung diseases such as asthma, and people who are active outdoors, especially outdoor workers. Elevated ozone can also harm the health of trees, plants and ecosystems. Learn more about the formation of ozone | View Criteria Pollutants >

Summary: 

When a region fails to meet the federal air quality standards for ozone, it is designated as being in nonattainment, with classifications that range from marginal to moderate, serious, severe, and extreme. As the classification becomes more stringent, regulatory requirements increase as a means to reduce emissions that contribute to ozone and bring the area back into attainment with the health and welfare standards. The concentration of ozone in the Phoenix-Mesa Ozone Nonattainment Area currently exceeds both the 2008 and 2015 8-hour ozone NAAQS.  

The following is a description of agency partners' roles and responsibilities as they pertain to planning and policy in the Phoenix-Mesa Ozone Nonattainment Area:

  • Maricopa Association of Governments (MAG) — Pursuant to A.R.S. § 49-406, MAG is designated by the Governor of Arizona as the air quality planning agency for the Phoenix-Mesa Ozone Nonattainment Area | Learn More About MAG >
  • Arizona Department of Environmental Quality (ADEQ) — sets and enforces state-level rules, issues air quality permits for facilities within ADEQ’s permitting jurisdiction, and inspects ADEQ permitted facilities to ensure compliance with permit conditions | Learn More About ADEQ >
  • Maricopa County Air Quality Department (MCAQD) — sets and enforces county-level rules, issues air quality permits for facilities within Maricopa County’s permitting jurisdiction, and ensures that Maricopa County permitted facilities remain in compliance with permit conditions | Learn More About MCAQD >
  • Pinal County Air Quality Control District (PCAQCD) — sets and enforces county-level rules, issues air quality permits for facilities within Pinal County’s permitting jurisdiction, and ensures that Pinal County permitted facilities remain in compliance with permit conditions| Learn More About PCAQCD >

ADEQ published a press release on Jan. 23, 2025, announcing the Ground Level Ozone Research (GLOR) Project to address rising ozone levels | View Press Release >

Regulatory Background:

In 2022, the U.S. Environmental Protection Agency (EPA) reclassified the Phoenix-Mesa Ozone Nonattainment Area from marginal to moderate for the 2015 ozone NAAQS, which moved the area up the severity ladder for ozone pollution. Arizona was given until Jan. 1, 2023, to submit a State Implementation Plan (SIP) demonstrating that new and existing emission control measures would reduce ozone concentrations to the 2015 ozone standard of 70 parts per billion or less by Aug. 2024. 

On Oct. 18, 2023, the Phoenix-Mesa Ozone Nonattainment Area, along with 16 other ozone nonattainment areas in 10 additional states, were included in a final EPA rule finding that these areas failed to submit a SIP to address Clean Air Act (CAA) requirements for moderate ozone nonattainment areas. 

Following EPA’s finding, multiple outstanding and required SIP elements for the Phoenix-Mesa Ozone Nonattainment Area were submitted to the EPA to address the moderate area requirements for the 2015 ozone NAAQS including:

  • A revision to the Arizona SIP addressing reasonably available control technology (RACT) requirements for the Gila County portion of the nonattainment area, submitted March 26, 2025 and approved by the EPA on May 22, 2026;
  • A revision to the Arizona SIP addressing RACT requirements for the Pinal County portion of the nonattainment area, submitted April 14, 2025; and
  • A revision to the Arizona SIP to address several additional requirements  for the 2015 Ozone Phoenix-Mesa Nonattainment Area, submitted April 25, 2025.

On May 1, 2025 the EPA issued a completeness finding for the moderate nonattainment area State Implementation Plan (SIP) requirements for the Phoenix-Mesa Ozone Nonattainment Area, terminating the CAA sanction clock that started as a result of the EPA’s Oct. 18, 2023 action. 

The Phoenix-Mesa Ozone Nonattainment Area was unable to meet the ozone standard by the moderate attainment date of Aug. 3, 2024, if international transport of ozone and ozone precursors were not considered. However, MAG prepared and submitted a CAA § 179B(b) Retrospective Demonstration to the EPA, and on March 23, 2026, the EPA published a final action in the Federal Register determining that the Phoenix-Mesa Nonattainment Area would have attained the 2015 ozone NAAQS by the moderate area attainment deadline, but for emissions emanating from outside of the United States | View Final Action >

Resources:

Recently submitted plans for the Phoenix-Mesa Ozone Nonattainment Area:

  • MAG Eight-Hour Ozone Plan Submittal of Applicable Moderate Area Requirements submitted to the EPA in April 2025 for the 2015 ozone standard | View 2025 Plan >
  • MAG Eight-Hour Ozone Plan Submittal of Applicable Marginal Area Requirements submitted to the EPA in July 2020 for the 2015 ozone standard  | View 2020 Plan >
  • ADEQ RACT Analysis and Negative Declarations for Gila County  submitted to the EPA in March 2026 for the 2015 ozone standard | View Gila RACT Plan >

Multiple other SIP revisions to address CAA requirements for the Phoenix-Mesa Ozone Nonattainment area have been prepared by MAG, ADEQ, MCAQD, and the PCAQCD and submitted to the EPA. All plans are available upon request from the ADEQ Records Center | Submit A Records Request > 

Key controls that have been implemented:

  • Summer fuel reformulation
  • Vehicle emissions inspections 
  • Federal standards for new vehicles
  • Reasonable Available Control Technology (RACT) for industrial sources of ozone precursors

Unfamiliar with some of the acronyms or technical terms used on this page?

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