An official website of the United States government.

We've made some changes to EPA.gov. If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Sulfur Dioxide (SO2) Pollution

Primary National Ambient Air Quality Standard (NAAQS) for Sulfur Dioxide

Rule Summary

On May 25, 2018, based on a review of the full body of currently available scientific evidence and exposure/risk information, the EPA proposed to retain the existing primary National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (SO2). EPA’s proposal 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

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)

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

Regulatory Impact Analysis (RIA) for the 2010 Revisions to the Sulfur Dioxide NAAQS

Scientific and Technical Documents Supporting the primary NAAQS for SO2

Related Rules

Secondary National Ambient Air Quality Standards (NAAQS) for Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2)