Ozone NAAQS Area Designations

Current understanding

Under the Clean Air Act, EPA designates areas as attainment or nonattainment for the National Ambient Air Quality Standards (NAAQS) for ozone, and states may petition for redesignation once monitored air quality data show compliance. Redesignation requires an approved maintenance plan (typically covering 10-20 years), motor vehicle emissions budgets, and demonstration that improvement is due to permanent, enforceable measures. Practical effects include relief from certain nonattainment permitting requirements (e.g., stricter New Source Review) while retaining transportation conformity obligations tied to the maintenance plan.

Evidence log

• 2026-08-27 — Air Plan Approval; Michigan; 2015 Ozone Moderate Reasonably Available Control Technology: 2025 — EPA approving Michigan SIP revisions establishing VOC and NOx RACT for the Berrien, western Allegan, and western Muskegon County 2015 ozone Moderate nonattainment areas, including controls on consumer products and architectural coatings. (novelty: 2)
• 2026-08-27 — Air Plan Approval; Kentucky; Louisville Area Limited Maintenance Plan for the 1997 8-Hour Ozone NAAQS: 2025 — EPA proposed approval of Kentucky’s limited maintenance plan for the Louisville-area counties under the 1997 8-hour ozone NAAQS, making the state’s maintenance commitments federally enforceable. (novelty: 2) (novelty: 2)
• 2026-08-27 — Air Plan Approval; Kentucky; Cincinnati-Hamilton Area Limited Maintenance Plan for the 1997 8-Hour Ozone NAAQS: 2025 — EPA proposed approval of Kentucky’s limited maintenance plan for the Cincinnati-Hamilton area (Boone, Campbell, and Kenton Counties) under the 1997 8-hour ozone NAAQS, making the state’s maintenance commitments federally enforceable. (novelty: 2)
• 2026-08-20 — Air Plan Approval; Wisconsin; Moderate Attainment Plan Elements for Wisconsin’s 2015 Ozone Standard Areas: 2025 — EPA proposed approval of Wisconsin’s Moderate area SIP elements for the Kenosha, Milwaukee, and Sheboygan 2015 8-hour ozone nonattainment areas, including 2023 motor vehicle emissions budgets, vehicle inspection/maintenance program, and nonattainment New Source Review provisions. (novelty: 2)
• 2026-08-13 — Determination of Attainment by the Attainment Date; 1997 Ozone Standards; California; Coachella Valley: 2025 — EPA final determination that California’s Coachella Valley Extreme nonattainment area attained the revoked 1997 8-hour ozone NAAQS by its June 15, 2025 attainment date, based on 2022–2024 monitoring data. (novelty: 2)
• 2026-08-13 — Air Plan Approval; Illinois; Clean Data Determination for the Illinois Portion of the St. Louis Area for the 2015 Ozone Standard: 2025 — EPA clean data determination finding the Illinois portion of the bi-state St. Louis area attained the 2015 8-hour ozone NAAQS, suspending certain attainment planning SIP requirements for the Illinois portion while monitored attainment persists (companion to the earlier Missouri-side determination). (novelty: 2)
• 2026-08-13 — Air Plan Approval; Missouri; Clean Data Determination for the 2015 8-Hour Ozone Standard for the Missouri Portion of the St. Louis Nonattainment Area: 2026 — EPA clean data determination finding the Missouri portion of the bi-state St. Louis nonattainment area attained the 2015 8-hour ozone NAAQS based on recent monitoring, suspending certain attainment planning SIP requirements for the Missouri portion while monitored attainment persists. (novelty: 2)
• 2026-08-14 — Air Plan Approval; Missouri; Moderate Attainment Plan Elements for the 2015 8-Hour Ozone Standard for the Missouri Portion of the St. Louis Nonattainment Area: 2026 — EPA proposed approval of Missouri’s Moderate area SIP elements (vehicle I/M program, nonattainment NSR rules, and major-source VOC/NOx RACT determinations) for the Missouri portion of the bi-state St. Louis 2015 8-hour ozone nonattainment area. (novelty: 2)
• 2026-08-14 — Air Plan Approval; Virginia; 1997 8-Hour Ozone National Ambient Air Quality Standard Second Maintenance Plan for the Madison and Page Counties (Shenandoah National Park) Area: 2025 — EPA proposed approval of Virginia’s second 10-year maintenance plan for the Madison and Page Counties (Shenandoah National Park) area under the 1997 8-hour ozone NAAQS, continuing maintenance-area status for this already-attaining rural area. (novelty: 2)
• 2026-08-06 — Air Plan Approval; Illinois; 2015 Ozone Moderate and Serious Reasonably Available Control Technology Update: 2025 — EPA proposed approval of Illinois SIP revisions establishing Moderate VOC/NOx RACT and Serious NOx RACT for the Chicago and Metro-East St. Louis 2015 ozone nonattainment areas, adding to the Section 182 RACT compliance track for these areas. (novelty: 2) (novelty: 2)
• 2026-07-28 — Air Plan Approval; Michigan; Redesignation of the Berrien, MI and Muskegon, MI Areas to Attainment of the 2015 Ozone Standards: 2025 — EPA proposed to redesignate the Berrien, MI and Muskegon, MI areas to attainment for the 2015 ozone NAAQS and to approve Michigan’s SIP maintenance plans, motor vehicle emissions budgets, enhanced monitoring, VOC RACT, and a NOx RACT waiver. (novelty: 2)
• 2026-07-28 — Air Plan Approval; Michigan; Redesignation of the Detroit, MI Area to Attainment of the 2015 Ozone Standards: 2025 — EPA proposed to redesignate the Detroit, Michigan area to attainment for the 2015 ozone NAAQS and approve Michigan’s maintenance plan through 2040, including motor vehicle VOC and NOx emissions budgets for 2035 and 2040. (novelty: 2)
• 2026-07-16 — Air Plan Approval; Pennsylvania; Interim Final Determination To Stay and Defer Sanctions Related to Reasonably Available Control Technology Requirements (RACT) for Volatile Organic Compounds (VOC) Control Technique Guidelines (CTG) Under the 2008 Ozone National Ambient Air Quality Standards (NAAQS): 2025 — EPA interim final determination that Pennsylvania’s VOC CTG RACT SIP revisions satisfy the 2008 ozone NAAQS, staying CAA §179 emission offset sanctions and deferring the highway funding sanctions clock for affected Pennsylvania nonattainment areas. (novelty: 2)
• 2026-04-27 — FIRE Act: 2025 — FIRE Act (HR6387) would expand exceptional-events eligibility to include prescribed burns and wildfire-mitigation-related meteorological events, potentially allowing more high-ozone days to be excluded from design values used in nonattainment designation and redesignation decisions. (novelty: 3)
• 2026-04-17 — FENCES Act: 2025 — FENCES Act (introduced) would exempt states from ozone nonattainment designations and related sanctions where exceedances are driven by foreign emissions or exceptional events like wildfires, potentially altering designation outcomes for wildfire-smoke-affected western states. (novelty: 3)
• 2026-07-09 — Approval and Promulgation of Implementation Plans; California; San Joaquin Valley; Revisions to Motor Vehicle Emissions Budgets for Ozone: 2025 — EPA proposed to approve revised motor vehicle emissions budgets for NOx and VOC in the San Joaquin Valley 2008 8-hour ozone NAAQS nonattainment area for 2026, 2029, and 2031, replacing budgets derived from an earlier EMFAC emissions model. (novelty: 2)
• 2026-05-14 — Air Plan Approval; Illinois; Moderate Attainment Plan Elements for the Chicago and Metro East Areas for the 2015 Ozone Standard: 2025 — EPA approving portions of Illinois’ 2015 ozone NAAQS Moderate SIP for the Chicago and Metro East St. Louis nonattainment areas, including RFP demonstrations, motor vehicle emissions budgets, I/M and NNSR programs, and 2017 base year emissions inventories. (novelty: 2)
• 2026-05-14 — Air Plan Approval; Ohio; Clean Data Determination for the Cleveland, Ohio Area for the 2015 Ozone Standard: 2025 — EPA determined the Cleveland, Ohio nonattainment area attained the 2015 ozone NAAQS based on 2023–2025 monitoring data, invoking the Clean Data Policy to suspend attainment demonstration and related planning SIP requirements while monitored attainment persists. (novelty: 2) (novelty: 2)
• 2026-05-29 — Air Plan Approval; Maryland; Clean Data Determination for the Baltimore, MD Nonattainment Area for the 2015 Ozone National Ambient Air Quality Standards: 2025 — EPA determined the Baltimore, MD nonattainment area attained the 2015 8-hour ozone NAAQS based on 2022–2024 monitoring data, invoking the Clean Data Policy to suspend attainment demonstration and related planning SIP requirements while monitored attainment persists. (novelty: 2)
• 2026-05-29 — Air Plan Approval; Michigan; Determination of Attainment by the Attainment Date for the 2015 Ozone Standards: 2025 — EPA proposed determination that the Detroit, Michigan Moderate nonattainment area attained the 2015 ozone NAAQS by the August 3, 2024 attainment date, relying on concurrence with a Michigan EGLE exceptional events demonstration to exclude qualifying high-ozone days from the design value. (novelty: 2)
• 2026-05-29 — Designation of Areas for Air Quality Planning Purposes; Michigan; Technical Amendment: 2025 — EPA technical amendment reclassifying the Detroit, Michigan area as Moderate nonattainment for the 2015 ozone NAAQS, reverting the 2023 attainment redesignation after the Sixth Circuit vacated it. (novelty: 2) (novelty: 2)
• 2026-06-04 — Conditional Approval; Contingency Measure State Implementation Plan for the 2008 Ozone Standards; San Joaquin Valley, California: 2025 — EPA conditionally approved California’s contingency measure SIP for the San Joaquin Valley 2008 ozone NAAQS nonattainment area, requiring the state to submit additional contingency measures within one year to secure full approval. (novelty: 2)
• 2026-06-04 — Revisions of the Nonattainment Designation for the 2008 and 2015 Ozone Standards and Clean Data Determinations for the 2008 and 2015 Ozone Standards: Cecil County, MD and New Castle County, DE: 2025 — EPA final rule splitting the Philadelphia-Wilmington-Atlantic City nonattainment area into three distinct areas and issuing clean data determinations for Cecil County, MD and New Castle County, DE under both the 2008 and 2015 ozone NAAQS, suspending certain planning requirements while monitored attainment persists. (novelty: 2)
• 2026-06-12 — Ozone Reclassification State Implementation Plan Rule: 2025 — EPA proposed rule interpreting Clean Air Act Section 182 obligations upon ozone nonattainment reclassification to apply only requirements tied to the area’s current (higher) classification, reversing part of the January 2025 final rule that had layered prior-classification requirements. (novelty: 3)
• 2026-06-26 — Air Plan Approval; Ohio; Source-Specific Non-CTG RACT: 2025 — EPA final rule approving Ohio source-specific SIP revisions for VOC and NOx RACT at three Cleveland-area facilities, fully satisfying Moderate area RACT requirements under the 2015 ozone NAAQS. (novelty: 2)
• 2026-06-26 — Air Plan Approval; Ohio; Source-Specific Non-CTG RACT and SIP Strengthening for Ohio: 2025 — EPA final rule approving Ohio’s source-specific SIP revisions establishing VOC and NOx RACT requirements for facilities in the Cleveland nonattainment and Cincinnati maintenance areas under the 2015 ozone NAAQS. (novelty: 2)

Open questions

Related