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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 implemenent, maintain, and enforce the National Ambient Air Quality Standards, or NAAQS, and to fulfill other requirements of the Clean Air Act.

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. SIPs in states with areas that do not meet the NAAQS must include additional requirements to reduce air pollution in those “nonattainment” areas.

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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 state statues and 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
  • Infrastructure plans providing for general implementation of a NAAQS
  • NAAQS-specific Part D Nonattainment Area Plans
  • Maintenance plans
  • Vehicle Inspection and Maintenance (I/M) Plans
  • Emissions Inventories
  • Monitoring Networks
  • State Statutes submitted for the purposes of demonstrating legal authority
  • Permitting programs
  • Attainment Demonstrations
  • Transportation Control Measures (TCMs)
  • Contingency 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 that meet the requirements of the Act. Opportunities for public comment are available during the review and approval process for each SIP. If a state does not submit or EPA disapproves a required SIP, the Act also requires EPA to promulgate a Federal Implementation Plan, or FIP, to address the specific requirements.

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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. Members of the public can also file citizen suits under the Clean Air Act to address violations of 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.

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