Green Book

You are here: EPA Home > Green Book > SO2 (2010) Design Value Notes

SO2 (2010) NAAQS Notes

Return to Report

More detailed design value data can be found on the Air Quality Design Value site.

  1. The 2010 NAAQS for SO2 is a 1-hour SO2 standard at a level of 75 parts per billion (ppb), based on the 3-year average of the annual 99th percentile of 1-hour daily maximum concentrations. The previous 24-hour and annual primary SO2 standards remain in effect until the effective date of an area's designation for the 2010 1-hour standard.

  2. A group of 29 areas were designated nonattainment for the 2010 SO2 NAAQS effective October 4, 2013.

    Effective September 12, 2016, four additional areas were designated nonattainment: Alton Township IL, Williamson County IL, Anne Arundel County and Baltimore County MD, and St. Clair MI. See: 81 FR 45039

    Effective January 17, 2017, three additional areas were designated nonattainment: Freestone and Anderson Counties TX, Rusk and Panola Counties TX, and Titus County TX. See: 81 FR 89870

    Effective April 9, 2018, six additional areas were designated nonattainment: Hillsborough-Polk County FL, Huntington IN, Evangeline Parish (Partial) LA, Piti-Cabras GU, San Juan PR, Guayama-Salinas PR. See: 83 FR 1098

    In a future fourth round, the EPA expects to designate all remaining undesignated areas (approximately 50 areas) where states have installed and begun timely operation of a new SO2 monitoring network.