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.

Ground-level ozone concentrations are higher during warm, sunny weather, especially in summer. In addition to local pollution sources, ozone can also reach the surface through stratospheric ozone intrusions—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 can irritate the respiratory system and are particularly harmful to children, the elderly, and people with lung conditions. Learn more about the formation of ozone | View ADEQ’s Cracking the AQ Code >

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 partner’s 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 was designated by the Governor of Arizona as the regional air quality planning agency for ozone, particulate matter, and carbon monoxide. While MAG is responsible for air quality plans related to the Phoenix-Mesa Ozone Nonattainment Area, it has no enforcement powers or authority to promulgate rules | 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 US 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 plan 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. 

Since attainment of the 2015 ozone standard could not be demonstrated with measures in 2023, MAG did not submit a plan to the EPA. 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 have failed to submit a plan to address the EPA’s ozone requirements for moderate nonattainment areas. 

Resources:

For more information and engagement opportunities | View MAG's Air Quality Technical Advisory Committee >

Ozone fact sheet | View Fact Sheet >

What to do when ozone pollution is at an unhealthy level | Learn More >

To receive ADEQ’s Daily Air Quality Forecasts and follow recommendations in the health statement | Subscribe >

Previously submitted plans to address ozone concentrations:

• MAG submitted a plan to the EPA in April 2025 for the 2015 ozone standard | View 2025 Plan >
• MAG submitted a plan to the EPA in July 2020 for the 2015 ozone standard | View 2020 Plan >
• MAG submitted a plan to the EPA in December 2016 for the 2008 ozone standard | View 2017 Plan >

Rulemakings:

ADEQ will provide updates to rulemakings and opportunities to participate in planning efforts pertaining to the Phoenix-Mesa Ozone Nonattainment Area as they become available.

Key controls that have been implemented:

• Summer fuel reformulation
• Vehicle emissions inspections 
• Federal standards for new vehicles
• Reasonable available control technology for industrial sources of ozone precursors

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

Visit our glossary | View >