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Reviewing National Ambient Air Quality Standards – Scientific and Technical Information

Process of Reviewing the National Ambient Air Quality Standards

Sections 108 and 109 of the Clean Air Act (CAA) govern the establishment, review, and revision, as appropriate, of the National Ambient Air Quality Standards (NAAQS) to provide protection for the nation’s public health and the environment.  The CAA requires periodic review of the science upon which the standards are based and the standards themselves.  Reviewing the NAAQS is a lengthy undertaking and includes the following major phases:

Planning:  The planning phase of the NAAQS review process begins with a science policy workshop, which is intended to gather input from the scientific community and the public regarding policy-relevant issues and questions that will frame the review.  Drawing from the workshop discussions, EPA prepares an Integrated Review Plan (IRP) that presents the schedule for the entire review, the process for conducting the review, and the key policy-relevant science issues that will guide the review. 

Integrated Science Assessment (ISA):  This assessment is a comprehensive review, synthesis, and evaluation of the most policy-relevant science, including key science judgments that are important to inform the development of the risk and exposure assessments, as well as other aspects of the NAAQS review.  

Risk/Exposure Assessment (REA):  This assessment draws upon information and conclusions presented in the ISA to develop quantitative characterizations of exposures and associated risks to human health or the environment associated with recent air quality conditions and with air quality estimated to just meet the current or alternative standard(s) under consideration.  This assessment includes a characterization of the uncertainties associated with such estimates. 

Policy Assessment (PA):  This assessment provides a transparent staff analysis of the scientific basis for alternative policy options for consideration by senior EPA management prior to rulemaking.  Such an evaluation of policy implications is intended to help ‘‘bridge the gap’’ between the Agency’s scientific assessments, presented in the ISA and REA(s), and the judgments required of the EPA Administrator in determining whether it is appropriate to retain or revise the NAAQS.  In so doing, the PA is also intended to facilitate the Clean Air Scientific Advisory Committee’s (CASAC’s) advice to the Agency and recommendations to the Administrator, as provided for in the CAA, on the adequacy of the existing standards or revisions that may be appropriate to consider.  The PA focuses on the information that is most pertinent to evaluating the basic elements of the NAAQS:  indicator, averaging time, form, and level.

Scientific review during the development of these documents is thorough and extensive.  Drafts of all documents are reviewed by CASAC and the public has an opportunity to comment on them.

Rulemaking:  Taking into consideration the information in the ISA, REA(s), and PA and the advice of CASAC, EPA develops and publishes a notice of proposed rulemaking that communicates the Administrator’s proposed decisions regarding the review of the NAAQS.  A public comment period, during which public hearings are generally held, follows publication of the notice of proposed rulemaking.  Taking into account comments received on the proposed rule, EPA issues a final rule.

More information on the NAAQS review process.

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