On December 21, 2020, EPA took the final step to implement the health-based national air quality standard for sulfur dioxide (SO2) set in 2010. EPA has identified or “designated” all remaining portions of the U.S.:
- “nonattainment” – not meeting the 1-hour health-based national air quality standard for SO2,
- “unclassifiable” – not enough information to make a determination, or
- “attainment/unclassifiable” - meeting the standard and not contributing to a violation of the standard.
Read a pre-publication version of the Federal Register Notice, EPA's response to comments, and a summary fact sheet below.
Read the Technical Support Documents supporting this action.
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Final Rule: Air Quality Designations for the 2010 Primary Sulfur Dioxide (SO2) National Ambient Air Quality Standard - Round 4 (PDF)(57 pp, 511 K)
(Pre-publication Federal Register Notice)
- Fact Sheet: EPA’s Final Area Designations for the 2010 Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard (NAAQS) – Round 4 (PDF)(4 pp, 217 K)
- Summary Table: EPA’s Final Area Designations for the 2010 Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard (NAAQS) – Round 4 (PDF)(3 pp, 139 K)
- Responses to Comments on EPA’s Intended Designations for the 2010 Sulfur Dioxide Primary National Ambient Air Quality Standard (NAAQS) – Round 4 (PDF)(31 pp, 382 K)