The CAA requires states to develop individualized SIP that outlines how they plan to achieve the NAAQS. The SIP is a collection of regulations and documents used by a state, territory, or local air district to reduce air pollution in areas that do not meet the NAAQS.

What National Standards must SIPs Meet?

EPA has established the NAAQS for six “criteria” air pollutants – which are widespread common pollutants known to be harmful to human health:

  1. Carbon monoxide pollution
  2. Lead air pollution
  3. Nitrogen oxide pollution
  4. Ozone pollution
  5. PM pollution
  6. Sulfur dioxide pollution

The CAA identifies specific requirements that states must submit to EPA as part of their SIP to attain and maintain the NAAQS. SIPs provide a plan for implementation, maintenance, and enforcement of the NAAQS in each state.

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Figure 4.14 Non‐attainment counties in the United States for NAAQS pollutants.

What Is Included in a SIP?

The contents of a typical SIP fall into three categories:

  1. State‐adopted control measures which consist of either regulations or source‐specific requirements (such as orders and consent decrees)
  2. State‐submitted “non‐regulatory” components (see list of examples below)
  3. Additional requirements promulgated by EPA to satisfy a mandatory requirement in Section 110 or Part D of the CAA

Examples of EPA‐approved documents and materials associated with the SIP include, but are not limited to, the following:

  • SIP narratives
  • PM plans
  • Carbon monoxide plans
  • Ozone plans
  • Maintenance plans
  • Vehicle inspection and maintenance (I/M) SIPs
  • Emissions inventories
  • Monitoring networks
  • State statutes submitted for the purposes of demonstrating legal authority
  • Part D non‐attainment area plans
  • Attainment demonstrations
  • Transportation control measures (TCMs)
  • Committal measures
  • Contingency measures
  • Non‐regulatory and non‐TCM control measures
  • 15% Rate of progress plans
  • Emergency episode plans
  • Visibility plans

Who Is Responsible for Enforcing a SIP?

SIPs are generally enforced by the state. However, the EPA is authorized to take enforcement action against violators for federally approved SIPs.

If a SIP has been approved by a state but not yet approved by the EPA, then it is only state‐enforceable and not federally enforceable until approved by the EPA.

Members of the public can also file citizen suits under the CAA to address violations of SIPs.


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