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”.  On June 2, 2010, EPA strengthened the NAAQS for sulfur dioxide (SO₂) to provide better public health protection.  EPA revised the primary SO₂ standard by establishing a new 1-hour standard at a level of 75 parts per billion (ppb).  The EPA also specified that the existing SO₂ primary standards  (i.e., 140 ppb, 24-hour average and 30 ppb, annual average) will be revoked one year after the effective date of initial designations for the new 1-hour NAAQS for most existing SO₂ attainment areas.

Under the revised SO₂ NAAQS, EPA intended to establish initial designations using a hybrid approach that combines air quality monitoring and source-specific dispersion modeling.  Connecticut’s SO₂ monitors currently measure compliance with the revised SO₂ NAAQS and DEEP completed source-specific modeling that supported a designation of "attainment".  Therefore, Connecticut requested that EPA promulgate a statewide designation of "attainment". On December 22, 2017, EPA sent CTDEEP a letter with the final SO₂ designations for the 2010 primary SO₂ NAAQS for the State of Connecticut. EPA desingated Connecticut as "unclassifiable/attainment" for SO₂.

EPA's Letter to Connecticut Regarding the SO2 Data Requirements Rule. August 15, 2018

EPA's letter regarding final designations for the 2010 1-Hour SO2 Standard and the technical support document.

Connecticut's Revised Recommendation Regarding Designations for the 1-Hour SO2 Air Quality Standard (PDF)

SO2 Designation Technical Support Document (PDF)

EPA's reply to Connecticut's SO₂ Designation Recommendation (PDF)

Connecticut’s Recommendation to EPA for an Initial Designation of “Unclassifiable” for the 1-Hour SO₂ NAAQS (PDF)