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State Implementation Plan Overview

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When EPA establishes a new national ambient air quality standard (NAAQS) or revises an existing NAAQS, it sets in motion a series of actions aimed at ensuring that air quality throughout the country meets those standards.

EPA must designate areas as meeting (attainment) or not meeting (nonattainment) the standard. The Clean Air Act (CAA) requires states to develop a general plan to attain and maintain the NAAQS in all areas of the country and a specific plan to attain the standards for each area designated nonattainment for a NAAQS. These plans, known as State Implementation Plans or SIPs, are developed by state and local air quality management agencies and submitted to EPA for approval.

The SIPs serve two main purposes:

  1. Demonstrate that the state has the basic air quality management program components in place to implement a new or revised NAAQS.
  2. Identify the emissions control requirements the state will rely upon to attain and/or maintain the primary and secondary NAAQS

This web site identifies the SIP elements states must adopt to satisfy the CAA requirements to attain and maintain the NAAQS. This site also provides the status of state submissions to meet those requirements and EPA's action on those submissions.

Learn more about the current NAAQS.
Learn more about the process to attain and maintain the NAAQS.
Learn more about the electronic copies of SIPs available to the public.

Each state's SIP must contain a number of elements required by the Clean Air Act, and must be developed and adopted through a process allowing public input. Once adopted by the state, each required SIP element must be submitted by the Governor's designee to EPA. EPA must review and act to approve or disapprove each element.

The SIPs are designed to prevent air quality deterioration for areas that are in attainment with the NAAQS and to reduce common or criteria pollutants emitted in nonattainment areas to levels that will achieve compliance with the NAAQS. As the NAAQS change, states must submit revisions to the SIP to demonstrate attainment and maintenance of those new or revised NAAQS and to meet other statutory requirements.

All states are required to submit SIPs with general infrastructure elements showing the state has the capacity to attain, maintain, and enforce a new or revised NAAQS. These SIP submittals must include the basic program requirements for managing air quality required in section 110(a)(2) of the CAA. Learn more about Infrastructure SIP requirements.

In addition to the basic required elements, CAA Section 172 requires states with nonattainment areas to adopt additional regulatory programs designed to achieve and maintain attainment of the relevant NAAQS. Learn more about SIP requirements for nonattainment areas.

The general plan requirements for each nonattainment area are specified in subpart 1 of the Clean Air Act Part D. The additional provisions for each respective NAAQS are specified in subpart 2 to subpart 5.

Congress recognized in the 1990 CAA Amendments that the more densely populated Northeast states share the same airshed, as well as emissions sources and commuting patterns. In order to regionally address air quality in the Northeast, they created an area from Maine to Northern Virginia, calling it the Ozone Transport Region (OTR). States in the OTR are required to implement additional control measures that apply across the region, whether an area in the OTR is attainment or nonattainment. Learn more about SIP requirements for states in the Ozone Transport Region.


This web site contains the following information:

SIP Development Process. A summary of the steps states must follow when EPA revises or sets a new national ambient air quality standard.

Nonattainment Area and Ozone Transport Region SIP requirements. The status of each state submittal and EPA action on required SIP elements for each nonattainment area, including Ozone Transport Region requirements for specific states.

Infrastructure SIP element reports. The status of the state submittal and EPA action on the submittal for required infrastructure elements.

Clean Data Policy & Redesignation Policy. Overview of EPA policies and implementation rules outlining EPA interpretations of the provisions of the Clean Air Act as they apply to areas that have attained standards.

EPA Regional Office Implementation Plan Links. Regional SIP Web Pages where state regulations which have been incorporated by reference into the SIP are located.


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