Agency: Environmental Protection Agency
The Environmental Protection Agency (EPA) is determining under the Clean Air Act (CAA) that the Illinois portion of the St. Louis, MO- IL nonattainment area (hereafter also referred to as the "St. Louis area" or "area") has achieved clean data for the 2015 ozone National Ambient Air Quality Standards (NAAQS or standard). This determination is based upon complete, quality-assured, and certified ambient air monitoring data for the 2023-2025 design value period showing that the Illinois portion of the area achieved attainment of the 2015 ozone NAAQS. This determination also relies on the EPA's concurrence of an exceptional events request submitted by the Illinois Environmental Protection Agency (Illinois EPA) on December 18, 2025, and concurred on by the EPA on January 12, 2026. Therefore, th