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Sulfur Dioxide Designations

This web site provides information on the process EPA, the states, and the tribes follow to determine whether or not an area is meeting the revised primary national air quality standard for sulfur dioxide (SO2) established in 2010. After EPA establishes or revises a primary and/or secondary National Ambient Air Quality Standard (NAAQS), the Clean Air Act requires EPA to designate areas as "attainment" (meeting), "nonattainment" (not meeting), or "unclassifiable" (insufficient data) after monitoring data is collected by state, local and tribal governments.

Current scientific evidence links short-term exposures to SO2, ranging from 5 minutes to 24 hours, with an array of adverse respiratory effects, including bronchoconstriction and increased asthma symptoms. Reducing levels of SO2 pollution is an important part of EPA’s commitment to a clean, healthy environment.

“Designation” is the term EPA uses to describe the air quality in a given area for any of six common air pollutants known as criteria pollutants. One of these pollutants is SO2. (The other criteria pollutants are particulate matter, lead, carbon monoxide, nitrogen dioxide, and ozone.)

Once SO2 nonattainment area designations take effect, state and local governments have 18 months to develop implementation plans outlining how areas will attain and maintain the standards by reducing air pollutant emissions contributing to SO2 concentrations.

EPA strengthened the primary air quality standard for SO2 in 2010.

Learn more about the 2010 primary SO2 standard

This Web site contains the following information:

State Designations - Round 1: State area designations for the 2010 primary SO2 air quality standard are summarized here.

Tribal Designations - Round 1: Tribal area designations for the 2010 primary SO2 air quality standard are summarized here.

State Designations - Round 2: State area designations for the 2010 primary SO2 air quality standard that the EPA must complete by July 2, 2016 are summarized here.

Regulatory Actions: Links to regulatory documents and information explaining regulatory actions related to SO2 emissions.

Guidance and Data - Links to policies and guidance on SO2 designations and implementation.

Frequent Questions: Answers to common questions regarding the 2010 primary SO2 standard in air and the designations process.

Related Links: Related sites offering further information and assistance.

Glossary: Explanations of the technical terms and acronyms used throughout the site.

EPA has similar sets of web pages for ozone designations, fine particle (PM2.5) designations, nitrogen dioxide (NO2) designations, and lead (Pb) designations.


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