The United States Environmental Protection Agency (US EPA) recently announced that several areas in the Midwest and parts of the surrounding region have failed to meet the 2015
ozone National Ambient Air Quality Standards (NAAQS) by the designated attainment date. The nonattainment areas affected by this change include Allegan County (MI), Berrien County (MI), Chicago (IL-IN-WI), Cleveland (OH), Milwaukee (WI), Muskegon County (MI), Sheboygan County (WI), and the Illinois portion of the St. Louis metropolitan area (MO-IL). As a result, these areas have been reclassified from “Moderate” to “Serious” nonattainment for the 2015 ozone NAAQS, effective as of January 16, 2025. This reclassification will significantly impact industries within these areas, especially concerning air quality regulations for volatile organic compounds (VOC) and nitrogen oxides (NO
X). Facilities in these areas must now assess their operations and determine if they need to modify existing permits or apply for new permits due to the lowered emission thresholds.
2015 Ozone NAAQS: A Brief History
The primary and secondary NAAQS for ozone were notably revised by the US EPA on October 26, 2015, to establish a stricter 8-hour standard of 0.070 parts per million (ppm). Prior to this revision, the ozone standard had been 0.075 ppm, which had been established in 2008. Following this revision, the US EPA conducted a thorough review of air quality data across the country and designated counties as either “attainment” (meeting standards), “nonattainment” (not meeting standards), or “unclassifiable” (insufficient data). In 2018, the US EPA finalized the designation of nonattainment areas and assigned each nonattainment area a severity classification. The classification categories included: Marginal, Moderate, Serious, Severe, and Extreme (Figure 1). The severity for each region was determined by averaging ozone concentration data collected from local air monitoring stations over a three-year period, producing a Design Value (DV) for each area. If an area’s DV exceeded 0.070 ppm by the designated attainment date, it would be considered a failure to meet the ozone standards, thus triggering reclassification.
Midwest Nonattainment Reclassification
August 3, 2024, was the attainment date for areas designated as “Moderate”. By reviewing data from 2021-2023, the US EPA found that eight areas in Illinois, Indiana, Michigan, Missouri, Ohio, and Wisconsin had exceeded the 0.070 ppm threshold. These areas include Allegan County (MI), Berrien County (MI), Chicago (IL-IN-WI), Cleveland (OH), Milwaukee (WI), Muskegon County (MI), Sheboygan County (WI), and the Illinois portion of the St. Louis metropolitan area (MO-IL) (see Table 1). Effective as of January 16, 2025, the impacted counties have been reclassified to “Serious” nonattainment. The attainment date for Serious is ‘as expeditiously as practicable’ but no later than 9 years after initial nonattainment designation, or August 3, 2027.
TABLE 1. Summary Of Nonattainment Areas in Illinois, Indiana, Michigan, Missouri, Ohio, And Wisconsin Classified as Moderate for the 2015 Ozone NAAQS
Nonattainment area | 2021-2023 design value (DV ppm) | Attainment by the attainment date |
Allegan County, MI | 0.075 | Failed to attain. |
Berrien County, MI | 0.073 | Failed to attain. |
Chicago, IL-IN-WI | 0.077 | Failed to attain. |
Cleveland, OH | 0.073 | Failed to attain. |
Milwaukee, WI | 0.074 | Failed to attain. |
Muskegon County, MI | 0.077 | Failed to attain. |
Sheboygan County, WI | 0.077 | Failed to attain. |
St. Louis, MO-IL | 0.074 | Failed to attain. |
New Source Thresholds
Nonattainment areas are subject to stricter regulations than attainment areas to help improve air quality and bring the region into compliance with the NAAQS. Facilities in the affected areas will need to be aware of reduced potential to emit (PTE) thresholds regarding emissions of VOC and NO
X—two major contributors to ozone formation. Facilities will need to review rolling emissions spreadsheets to evaluate a potential change in their source determination. For “Serious” nonattainment areas, the major source threshold for VOC and NO
X emissions drops from 100 tons per year (tpy) to 50 tpy, as shown in Table 2. The modification thresholds also become more stringent, reducing from 40 tpy to 25 tpy (aggregated). These lower thresholds may result in facilities previously
designated as minor sources under the Moderate classification to now be classified as major sources, thus requiring the facilities to apply for a Title V permit.
TABLE 2. Major Source Thresholds for Non-attainment Areas
Ozone Nonattainment Designation | Major Source Threshold | Major Modification Threshold |
Marginal | 100 tpy VOC or NOX | 40 tpy VOC or NOX |
Moderate | 100 tpy VOC or NOX | 40 tpy VOC or NOX |
Serious | 50 tpy VOC or NOX | 25 tpy VOC or NOX (with aggregation) |
Severe | 25 tpy VOC or NOX | 25 tpy VOC or NOX (with aggregation) | Extreme | 10 tpy VOC or NOX | Any increase in VOC or NOX |
Facilities may be able to avoid applying for a Title V permit if they are eligible for a synthetic minor permit. A synthetic minor source is a source that otherwise has the potential to emit pollutants in amounts that are at or above the thresholds for major sources but has taken a restriction so that its PTE is less than such amounts for major sources. A site may apply for a synthetic minor permit if the facility PTE of NOX and VOC are below, and expected to remain below, the 50 tpy threshold. If a site is unable to achieve this threshold, they will need to apply for a Title V permit. Applications for new permits or revisions to existing permits must be submitted to the appropriate agency within 12 months of the reclassification date—by January 16, 2026. Facilities that have existing synthetic minor permits may also need to revise their permits to reflect emission rates below the new major source thresholds. Facilities are encouraged to review their emissions spreadsheets and determine if their PTE of NOX and VOC is close to or exceeding the new thresholds. This step is critical for ensuring compliance with the updated regulations.
New Major Modification Thresholds
Facilities considering new construction or significant modifications to their operations in the impacted areas should be aware of the
Nonattainment New Source Review (NNSR) requirements. The major modification threshold for triggering NNSR in a Serious nonattainment area is 25 tpy of VOC or NO
X (see Table 2), with aggregation over a 5-year period. Under this program, major modification projects must incorporate the Lowest Achievable Emission Rate (LAER), provide emissions offsets, and have opportunity for public involvement. LAERs are the most stringent emissions limitation provided by either the State Implementation Plan (SIP) or that achieved in practice. Public participation is a key part of the NNSR process, as it ensures transparency and allows communities to have input into the permitting process for new or modified sources.
State Implementation and the Role of States
When a nonattainment area is reclassified as Moderate, Serious, and Severe by the Clean Air Act, or by voluntary reclassification, each State impacted is required to submit a SIP. The SIP should incorporate the most up to date air quality standards and establish state emission standards of specific types of sources or industries. This plan should define how the state will achieve, and maintain, NAAQS attainment by the designated attainment date. SIP revisions are due to the US EPA within 18 months of reclassification or January 1 of the new classification year, i.e. January 1, 2026.
Conclusion
The reclassification to “Serious” nonattainment of these eight Midwest areas may require a major shift for facilities in these regions. Facilities will need to recognize the new, stricter thresholds for VOC and NOx emissions, and respond by evaluating operations, revising existing or applying for new permits if necessary, and ensuring compliance with the updated requirements. Timely action will be crucial to ensure that facilities remain compliant and avoid costly penalties or delays in the permitting process. To discuss your facility’s needs, reach out to
Chloe Reece or Anna
Aumann in our
Chicago office.