When EPA establishes a new national ambient air quality standard (NAAQS) or revises an existing standard for each criteria air pollutant, 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 requires states to develop a general plan to attain and maintain the standards in all areas of the country and a specific plan to attain the standards for each area designated nonattainment. 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.

SIP Development Process

• Within two years after setting a new NAAQS or revising an existing standard: With input from the states and tribes, EPA must identify or "designate" areas as meeting (attainment areas) or not meeting (nonattainment areas), the standards. Designations are based on the most recent set of air monitoring or modeling data characterizing an area.

• Within three years after setting a new NAAQS or revising an existing standard: All states must submit state implementation plans to show they have the basic air quality management program components in place to implement a new or revised NAAQS, as specified in Clean Air Act section 110. These plans are often called "infrastructure SIPs." Learn more about Infrastructure SIP requirements. See Guidance on Development and Submission of Infrastructure State Implementation Plans for National Ambient Air Quality Standards (PDF) (62pp, 533k)

• Within 18-36 months after designations: Due dates for nonattainment area SIPs are based on the area designation date and vary by pollutant and area classification. SIPs for areas designated as nonattainment for sulfur dioxide (SO₂), nitrogen dioxide (NO₂), coarse particle pollution (PM₁₀), and lead (Pb) are generally due no later than 18 months from the date of designation. SIPs for Ozone (O₃), fine particle pollution (PM_2.5), and carbon monoxide (CO) nonattainment areas are generally due within 36 months from the date of designation. Each nonattainment area SIP must outline the strategies and emissions control measures that show how the area will improve air quality and meet the NAAQS. In addition, the Clean Air Act mandates that areas adopt certain specified control requirements. Learn more about SIP requirements for nonattainment areas.

SIPs must be developed with public input, be formally adopted by the state, and submitted by the Governor's designee to EPA. After reviewing submitted SIPs, EPA proposes to approve or disapprove all or part of each plan. The public has an opportunity to comment on EPA's proposed action. EPA considers public input before taking final action on a state's plan. If EPA approves all or part of a SIP, those control measures are enforceable in federal court. If a state fails to submit an approvable plan or if EPA disapproves a plan, EPA is required to develop a federal implementation plan (FIP).