Final Particulate Matter National Ambient Air Quality Standards
November 2006


The Clean Air Act, 42 U.S.C. § 7401, et seq.,

requires EPA to establish national ambient air quality standards (NAAQS) for pollutants that the Agency has identified as “criteria pollutants” based on their likelihood of harming public health and welfare. EPA can only consider public health and welfare when establishing NAAQS. The agency cannot analyze the benefits and costs of any new standards. Instead, benefits and costs are addressed when developing implementation standards for the rule.

Particulate matter (PM) is one of the criteria pollutants regulated by EPA. On September 21, 2006, EPA issued new national ambient air quality standards for PM pollution. The final standards address two categories of PM: (1) fine particles (PM

2.5), which are less than or equal to 2.5 micrometers (um) in diameter; and (2) coarse particles (PM10) which are less than or equal to 10 um. For comparison sake, the average diameter of human hair is approximately 70 um and beach sand is approximately 90 um.


Pursuant to the Clean Air Act, EPA must review standards once every five years to determine whether revisions to the standards are appropriate. However, the exhaustive, multi-step, multi-party NAAQS development process leaves much to be desired. As a practical matter, EPA cannot meet this five-year mandate.

The review of the standard begins with an assessment of science about the pollutant conducted by EPA’s National Center for Environmental Assessment (NCEA). The NCEA prepares an “Air Quality Criteria Document” which is a preliminary assessment of available scientific data. Next, EPA’s Office of Air Quality Planning and Standards prepares a “staff paper” that reviews the scientific information in the criteria document.

The scientific community, industry, public interest groups, the general public, and the Clean Air Scientific Advisory Committee (CASAC), an independent group of scientific and technical experts, then review the criteria document and the staff paper. CASAC makes recommendations to EPA for any appropriate revisions to existing standards. After CASAC makes its recommendations, EPA proposes a rule for public comment and adopts final standards.

In this case, EPA did not meet the five-year timeline. Again, this is not at all surprising given the extensive process used to review the standards. In fact, the current PM

10 standard had been first adopted in 1987. EPA first adopted the PM2.5 standard in 1997 and had not revised it since that time.

Because EPA did not meet the five-year deadline to review its PM standards, it was sued by a group of plaintiffs representing environmental public interest organizations. Under the terms of the resulting consent decree, EPA agreed to issue proposed revised standards by December 20, 2005, and committed to finalize any revisions to the standards by September 27, 2006.

Due in no small measure to the decreed timeline, EPA based the final rule largely on scientific studies published prior to 2003. EPA did review studies conducted after that time but did not rely on those newer studies in making its decision. So the end result is a rule, devoid of cost considerations, that is based on dated health studies.

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