Primary National Ambient Air Quality Standard (NAAQS) for Sulfur Dioxide
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Rule Summary
February 25, 2019, based on a review of the full body of currently available scientific evidence and exposure/risk information, the EPA issued a decision to retain the existing primary National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (SO2). EPA’s decision is based on its judgment that the current NAAQS protects the public health, with an adequate margin of safety, including the health of at-risk populations with asthma.
The existing standard, established in 2010, is 75 parts per billion based on the 3-year average of the 99th percentile of the yearly distribution of 1-hour daily maximum concentrations.
Rule History
02/25/2019 -Primary National Ambient Air Quality Standard for Sulfur Oxides - Final Decision
06/21/2018 - Notice of Public Hearing and Extension of Public Comment Period on Proposed Decision
06/8/2018 - Primary National Ambient Air Quality Standard for Sulfur Oxides - Proposed Decision
01/26/2011 – Denial of Petitions to Reconsider
06/22/2010 – Final Revision to Sulfur Dioxide Primary National Ambient Air Quality Standards (NAAQS) (pdf) (615 KB)
12/08/2009 – Proposed Revision to Sulfur Dioxide Primary National Ambient Air Quality Standards (NAAQS)
Additional Resources
Fact Sheets and Additional Information Regarding the Primary NAAQS for Sulfur Dioxide
Current and Past Design Values at Monitoring Sites Nationally
Regulatory Impact Analysis (RIA) for the 2010 Revisions to the Sulfur Dioxide NAAQS (pdf)
Scientific and Technical Documents Supporting the primary NAAQS for SO2