The Role of SIPs in Achieving Better Air Quality

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For more than 30 years, attaining the U.S. Environmental Protection Agency’s (EPA) National Ambient Air Quality Standards has been a major priority of the Clean Air Act (CAA). State and local air pollution control agencies have played a key role in meeting this objective by developing comprehensive, regional clean air plans, known as state implementation plans (SIPs). Once EPA approves them, SIPs become federally enforceable and represent the pathway to achieving healthier air quality in the United States. This article offers an overview of the evolution of the SIP process through several amendments to the CAA.


The state implementation plan (SIP) process has its roots in the 1970 Clean Air Act Amendments (CAAA). Before 1970, air pollution cleanup efforts in the United States rested largely on the shoulders of a few progressive state and local control agencies. Federal responsibilities were limited primarily to research, technical and financial assistance to states and localities, interstate actions to address multistate problems, and initial work to define “regional air sheds,” known as Air Quality Control Regions.1 The National Ambient Air Quality Standards (NAAQS) did not exist, and comprehensive air quality management efforts were reserved for the most severe problem areas such as Los Angeles, CA. Federal enforcement was limited to a small number of interstate abatement actions, such as those conducted by the U.S. Public Health Service along the Ohio River Valley, the New York City Interstate Area, and Washington, DC. These interstate actions achieved varied and spotty success, and suffered from the absence of real enforcement mechanisms. Without the NAAQS, there were no regulatory benchmarks to gauge air quality success.

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