Sulfur Dioxide (SO2) Pollution

Setting and Reviewing Standards to Control SO2 Pollution

What are SO2 standards?

National Ambient Air Quality Standards (NAAQS) for SO2 specify maximum amounts of sulfur dioxide to be present in outdoor air. Limiting SO2 in the air protects human health and the environment.
  • 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).

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How are the standards developed and reviewed?

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.

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What scientific and technical information supports reviews?

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.

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