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National Ambient Air Quality Standards (NAAQS)

Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2) Secondary Standards

The Clean Air Act requires EPA to set national air quality standards for six criteria pollutants (nitrogen oxides, sulfur oxides, particulate matter, ozone, carbon monoxide, and lead) based on primary (health-based) and secondary (welfare-based) considerations. The law also requires EPA to periodically review the scientific criteria upon which the standards are based  (learn more about this process).  While EPA generally reviews criteria and standards for each of the six criteria pollutants individually, for this review of the secondary standards for NO2 and SO2, EPA has decided to examine nitrogen oxide (NOx) and sulfur oxide (SOx) compounds together.  EPA recognizes that NOx, SOx are inextricably linked from both an atmospheric chemistry and environmental effects perspectives.

Basic Information, Fact Sheets, and Other Information Related to Oxides of Nitrogen

Basic Information, Fact Sheets, and Other Information Related to Oxides of Sulfur

Contact: Ginger Tennant
(919) 541-4072

Documents from Current Review

  • Planning Documents
  • Integrated Science Assessments
  • Risk and Exposure Assessments
  • Policy Assessments
  • Other Technical Documents
  • CASAC Documents
  • Federal Register Notices
  • Response to Comments Document
  • Regulatory Impact Analysis
  • Litigation

Documents from Review Completed in 2012

Documents from NO2 Review Completed in 1996  

Documents from SO2 Review Completed in 1996

Summary of Current NAAQS Table



File Utilities

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