SO2 Planning Efforts

Section 107(d)(1) of the Clean Air Act (CAA) provides up to one year after EPA’s adoption of a new or revised National Ambient Air Quality Standard (NAAQS) for states to recommend initial designation of areas as “attainment”, “nonattainment” or “unclassifiable”. 

In December 2024, EPA finalized a revised secondary SO₂ NAAQS to improve protection of public welfare, including visibility, ecosystems, and vegetation. This action replaced the previous 3-hour secondary standard with a new annual secondary standard set at 10 ppb, averaged over three years. In accordance with Section 107(d)(1) of the CAA, Connecticut evaluated current SO₂ air quality and determined that the state meets the revised secondary standard. Connecticut submitted a recommendation of “attainment” for the 2024 secondary SO₂ NAAQS and is currently awaiting EPA’s final designation.