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Ozone Nonattainment

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Environment, Great Lakes, and Energy

Ozone Nonattainment


Jay Olaguer, Air Quality Division


This webpage has information about Michigan's ozone attainment status, the Clean Air Act (CAA) requirements for the nonattainment classifications, EGLE's timeline, workgroups, field study, and additional related resources.

Information on proposed rule changes related ozone nonattainment can be found on the Laws and Rules page.

Michigan's Current Ozone Attainment Status

West Michigan currently has areas designated as "Moderate Nonattainment" and there are areas of southeast Michigan designated as "Attainment/Maintenance."  To learn more about the history of ozone attainment in Michigan and how three-year design values are used to determine attainment status, see "Michigan's Ozone History" below. To get to where Michigan is today, several things happened:

  • 2021: At the end of the ozone monitoring season, data from ambient air monitoring stations in the seven-county southeast Michigan nonattainment area, showed attainment with the standard based on data from 2019 through 2021. Michigan submitted a request to the USEPA on January 3, 2022, requesting the area formally be redesignated to attainment.
  • July 4, 2021: A data review showed an exceedance at one of the air monitors. The exceedance required a pause in the review of the redesignation request.
  • January 25, 2023: The exceedance initiated further review into the cause. The review showed that Canadian wildfire smoke on June 24 and June 25, 2020, was the cause of the exceedance. An Exceptional Events Demonstration was submitted on January 26, 2023. If accepted, this demonstration would bring the design value for southeast Michigan back below the 2015 Ozone NAAQS.
  • February 3, 2023: USEPA proposed approval of a Clean Data Determination in the Federal Register.
  • May 19, 2023: USEPA finalized the Clean Data Determination and Michigan’s redesignation for the southeast Michigan counties.

Attainment / Maintenance Areas

The southeast Michigan redesignation request includes Michigan’s maintenance plan detailing how air quality will be maintained considering projected growth for a period of 20 years. If future monitoring shows that ozone levels are no longer meeting the criteria, the maintenance plan helps determine when and how the problem will be addressed through adoption of contingency measures.

Moderate Nonattainment Areas

Michigan currently has three areas in West Michigan that were reclassified to moderate nonattainment on November 7, 2022. The Clean Air Act requires several responses / actions be taken for areas designated as moderate, including:

  • VOC / NOx RACT rulemaking for Major and CTG Sources
  • 15% VOC Decrease (over six years 2017 - 2023)
  • Attainment Demonstration
  • Basic Inspection and Maintenance (for larger population areas: 200,000+ based off 1990 census – this does not apply to West Michigan)
  • Contingency Measures for Failure to Attain (can consist of VOC and/or NOx reductions)
  • NSR offset ratio increases from 1.1:1 for marginal to 1.15:1 for moderate.

Michigan's 2015 Ozone National Ambient Air Quality History

The United States Environmental Protection Agency (USEPA) revised the primary and secondary ozone National Ambient Air Quality Standard (NAAQS) to 70 parts per billion (ppb) October 26, 2015 and published ozone nonattainment designations with an effective date of August 3, 2018. The Michigan counties initially designated as nonattainment were Berrien, Livingston, Macomb, Monroe, Oakland, St. Clair, Washtenaw, and Wayne, and western portions of Allegan and Muskegon counties.

Ozone nonattainment areas are classified based on the severity of their ozone concentrations. The ozone concentration uses a calculation called the "design value." The nonattainment counties were classified as marginal nonattainment, which means that ozone concentrations were less than 10 parts per billion (ppb) above the standard at the time of initial designations. Marginal nonattainment is the lowest classification requiring less actions than more severe classifications.

Michigan had until August 3, 2021, to bring the design values at or below the 2015 Ozone NAAQS. Michigan was not able to attain the standard based on data from 2018 – 2020 and was "bumped-up" to a moderate nonattainment classification for all nonattainment areas. This “bump-up” became effective November 7, 2022 for the west Michigan nonattainment areas and March 1, 2023 for the southeast Michigan nonattainment areas. As of May 19, 2023, southeast Michigan was redesignated as attainment, please see below for more information on that process.


Ozone Attainment Roadmap


* Dates Subject to Change

  • Work to address moderate nonattainment requirements and upcoming deadlines associated with the 2015 ozone standard is ongoing. This work has consisted of development of VOC and NOx RACT rules, exceptional events demonstrations where applicable, an attainment plan for West Michigan, and more.

    A major component of Michigan's response to the nonattainment status of these areas may be rule making. Information regarding recently finalized and upcoming rules can be found on the EGLE AQD Laws and Rules webpage.

  • The following workgroups have been established with the intent of facilitating early discussion of potential control strategies for a moderate nonattainment SIP for the southeast Michigan Ozone nonattainment area:

    • Primary Formaldehyde, VOC / NOx RACT and Landfill Emissions: This workgroup has three interrelated facets. The first is looking at stationary sources of formaldehyde, often formed as a result of combustion of common fuels. The second is looking at large sources of NOx and VOC within the nonattainment area to develop RACT rules. The third is looking at controlling methane from landfills. For additional information, contact Trace McDonald at 517-582-3570 or Marissa Vaerten at 517-582-3601.
    • Oil & Gas Emissions: This workgroup is investigating emissions of methane from the oil and gas sectors throughout the state. Work is focusing on quantifying emission reductions that can be used to lower ozone values. For additional information, contact Alec Kownacki at 517-614-6678.
    • Southeast Michigan (SEMI) Modeling and Measurement Steering Committee: This workgroup will make decisions regarding the collection of data that can be used for nonattainment planning. For additional information, contact Jay Olaguer at 517-512-0059.