U.S. National Ambient Air Quality Standards Review

EM – December 2020: This month, EM provides an update on the status of the current NAAQS review process and possible future changes to the process.
by Anthony J. Schroeder

The development of U.S. National Ambient Air Quality Standards (NAAQS)—and the requirement to periodically reevaluate them—are cornerstones of the U.S. Clean Air Act (CAA). The NAAQS, which the U.S. Environmental Protection Agency (EPA) must set for pollutants that are considered harmful to public health and the environment, establish national thresholds that are used to evaluate local air quality within the United States. The NAAQS are not necessarily fixed values, however. EPA is required to periodically review and consider revision of the NAAQS. The Clean Air Scientific Advisory Committee (CASAC), which is appointed by the EPA Administrator, is a part of this review process and recommends to the administrator new or revised standards as appropriate.

The three articles that follow this month focus on NAAQS and aspects of the review and revision process. The first two articles provide information and commentary on the periodic review process itself. In the first article, James Boylan, who is a current member of CASAC, provides an overview of recent CASAC activity, including reviews of the particulate matter (PM) and ozone NAAQS. The author also provides his recommendations for future NAAQS reviews. In the second article, H. Christopher Frey, a former CASAC chair, provides commentary on the recent PM and ozone NAAQS reviews and his recommendations for future reviews.

The third article by Karen Hays and co-authors provides a review of the state of air quality in the United States on the 50th anniversary of the establishment of the EPA. The authors credit the implementation of environmental programs by EPA, state, local, and tribal agencies, driven by the NAAQS, with the noted air quality improvements over the past five decades. 

Continue reading the full December 2020 issue of EM.


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