- What are SO2 standards?
- How are the standards developed and reviewed?
- What scientific and technical information supports reviews?
- See primary NAAQS for SO2 for an in-depth explanation of the current SO2 primary (health-based) standards, including Federal Register citations and fact sheets.
- See secondary NAAQS for SO2 for an in-depth explanation of the current SO2 secondary (welfare-based) standard and EPA’s most recent joint review of the secondary standards for SO2 and nitrogen dioxide (NO2).
The Clean Air Act requires EPA to set national ambient air quality standards for sulfur oxides as one of the six criteria pollutants. The NAAQS for sulfur oxides are currently set using SO2 as the indicator of the larger group of sulfur oxides. The law also requires EPA to periodically review the standards and revise them if appropriate to ensure that they provide the requisite amount of health and environmental protection and to update those standards as necessary.
- Learn more about the standards review process
- View a timeline of the SO2 NAAQS to get an overview of how the standards have changed over time
The various documents published during the review process include multiple drafts of plans and assessments, reports from the Clean Air Scientific Advisory Committee (CASAC), and Federal Register notices.