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Basic Information about Air Quality SIPs

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What is a SIP?

A State Implementation Plan (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 National Ambient Air Quality Standards, or NAAQS.

See also: Basic information about Federal Implementation Plans (FIPs) and Tribal Implementation Plans (TIPs).

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What national standards must SIPs meet?

EPA has established the National Ambient Air Quality Standards 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. Particulate matter pollution
  6. Sulfur dioxide pollution

SIPs provide a plan for implementation, maintenance, and enforcement of the NAAQS in each state.

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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 Clean Air Act.

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

  • SIP Narratives
  • Particulate Matter 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 Nonattainment 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

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What is EPA's role?

The Clean Air Act requires the EPA to review and approve all SIPs. Opportunities for public comment are available during the review and approval process for each SIP. 

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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 Clean Air Act to address violations of SIPs.

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