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Air Quality

Air Pollutants and Monitoring - Criteria Pollutants

Boundaries and Designations for Sulfur Dioxide (SO2)

The federal Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to identify areas in each state using these three designations:

  • Attainment - area meets a National Ambient Air Quality Standard (standard)
  • Nonattainment - area does not meet (or is contributing to nearby areas in not meeting) a standard
  • Unclassifiable - there is not enough data to designate the area under a new or revised standard

EPA sets boundaries for areas designated nonattainment and unclassifiable based on recommendations from the states. States use ambient air monitoring networks, emissions inventories, EPA guidance, and other relevant information to make these recommendations. Furthermore, states and EPA request public input during the process.

See EPA's website for a list or maps of nonattainment areas, and an overview of the designation process.

Designation Process

On July 25, 2013, EPA completed an initial round of designations for nonattainment areas for the 1-hour SO2 NAAQS (78 FR 47191, August 5, 2013). The EPA designated parts of 16 states nonattainment based on monitored violations of the standard. No areas of SC were designated as nonattainment.

On February 6, 2013, EPA issued a letter to SC indicating that it would not designate any areas of the state for the new 1-hour SO2 standard. The EPA also announced that it would be working on developing an updated strategy for accurately identifying SO2 levels throughout the country which will focus on modeling and/or monitoring sources which emit SO2 above a certain threshold. Under this anticipated approach, EPA expects states to identify sources by early 2015, and provide modeling demonstrations or establish monitoring networks by late 2015. Those sources which are modeled would be designated 18 months after modeling demonstrations are submitted (December 2017) and attainment SIPs would be due August 2019. Those sources that are monitored would be designated after three years of monitored data is obtained (expected in December 2020) and attainment SIPs would be due August 2022. For more information, please visit EPA's SO2 designations page.

For more information, background, and updates on how EPA plans to implement the new 1-hour SO2 standard (including the designation process) please visit DHEC's SO2 implementation page.


For more information please contact the Bureau of Air Quality at (803) 898-4123 or by email.