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Sulfur Dioxide (SO2) Pollution

Applying or Implementing Sulfur Dioxide Standards


Designations: how do we know if an area is not meeting SO2 standards?

Areas within each state are "designated" as either meeting (attaining) sulfur dioxide (SO2) standards or not meeting them. In some cases, an entire state may attain a standard.

Those areas that exceed the standards are known as “nonattainment areas.” Nonattainment areas for SO2 and the other criteria air pollutants are listed in the Green Book.

Along with developing the SO2 standards themselves (part of the National Ambient Air Quality Standards, or NAAQS), EPA also develops requirements for how to go about attaining and maintaining those standards:

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What are the state implementation plan (SIP) requirements?

Air quality standards get applied, or implemented, through controlling air pollution from emission sources. Each state is required to develop a plan for how they will control air pollution within their jurisdiction. This plan is called a State Implementation Plan (SIP).

In general, the SIP consists of

  • programs, including
    • air quality monitoring
    • air quality modeling
    • emission inventories
    • emission control strategies
  • and documents (policies and rules)

that the state uses to attain and maintain the NAAQS.

A state must engage the public, through notices and public hearings, before sending the SIP to EPA for approval. Tribes may develop plans if they choose to do so, otherwise EPA will develop an implementation plan for them. Learn more Basics of SIP Requirements

  • Learn more about the NAAQS implementation process
  • SIP Status for each State, including tribal implementation plans (TIPs): EPA evaluates the submitted SIPs, then issues a notice, indicating that either the SIP has been approved or needs additional work. Once the SIP has been approved, the state implements its air pollution control strategies to gradually reduce sulfur dioxide pollution.

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How do states develop SIPs and start attaining the standards?

  • EPA's checklist guide to preparing a sulfur dioxide SIP: State, local, and tribal air quality agencies can find assistance in developing their plans to implement SO2 standards. Tools include timeframes for submitting parts of the SIP, and how to use emissions data to demonstrate progress in reducing SO2.
  • Redesignations and Clean Data Policy (CDP): States with areas that are starting to monitor attainment can demonstrate attainment using air quality modeling and other analyses.
  • Training resources include various presentations and webinars to explain the implementation process and assist the air agencies.
  • EPA evaluates the submitted SIPs, then issues a notice, indicating that either the SIP has been approved or needs additional work. Once the SIP has been approved, the state implements its air pollution control strategies to gradually reduce SO2 pollution. Get information about the SIP status for each state.

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