EPA Completes Fourth Round of Sulfur Dioxide Designations
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.
The Round 4 2010 SO2 NAAQS designations action was signed by the EPA Administrator, Andrew Wheeler, on December 21, 2020, pursuant to a court-ordered deadline of December 31, 2020. For administrative purposes only, and in compliance with requirements of the Office of the Federal Register, Acting Administrator Jane Nishida re-signed the same action on March 10, 2021 for publication in the Federal Register.
- Read the Technical Support Documents supporting this action.
- Final Rule (86 FR 16055; March 26, 2021)
Note: On April 8, 2021, the EPA changed the December 2020 nonattainment designation for portions of Outagamie County, Wisconsin, to attainment/unclassifiable. Learn more
- Fact Sheet: EPA’s Final Area Designations for the 2010 Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard (NAAQS) – Round 4 (pdf)
- Summary Table: EPA’s Final Area Designations for the 2010 Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard (NAAQS) – Round 4 (pdf)
- Responses to Comments on EPA’s Intended Designations for the 2010 Sulfur Dioxide Primary National Ambient Air Quality Standard (NAAQS) – Round 4 (pdf)