The National Ambient Air Quality Standards (NAAQS) for Particulate Matter (PM): EPA’s2006 Revisions and Associated Issues

Robert Esworthy
Specialist in Environmental Policy

James E. McCarthy
Specialist in Environmental Policy

Following its review of more than 2,000 scientific studies, on October 17, 2006, the Environmental Protection Agency (EPA) published its final revisions to the National Ambient Air Quality Standards (NAAQS) for particulate matter (particulates, or PM). Several states and industry, agriculture, business, and environmental and public health advocacy groups petitioned the court, challenging certain aspects of EPA's revisions. A February 24, 2009, decision by the U.S. Court of Appeals for the District of Columbia Circuit granted the petitions in part, denying other challenges, and remanded the standards to EPA for further consideration. While the court did not specifically vacate the 2006 PM standards, EPA has announced its intention to accelerate its ongoing next round of the periodic review of the particulates NAAQS, in part, in response to the court's decision. These actions, and EPA's ongoing implementation of the 2006 PM NAAQS, have prompted renewed interest among Members of Congress. 

Although a tightening of the standards, the 2006 particulates NAAQS are not as stringent as recommended by EPA staff or the independent scientific advisory committee mandated under the Clean Air Act (Clean Air Scientific Advisory Committee, or CASAC). The divergence from the CASAC's recommendations proved controversial, as did several other elements of the 2006 particulates NAAQS, including the decision not to exclude rural sources from the coarse particle standard. Some have also questioned the EPA's strengthening of the standard for all fine particles, without distinguishing their source or chemical composition. 

The EPA found that the evidence continued to support associations between exposure to particulates in ambient air and numerous significant health problems. Based on several analytical approaches, the EPA estimated that compliance with the revised NAAQS will prevent 1,200 to 13,000 premature deaths annually, as well as substantial numbers of hospital admissions and missed work or school days due to illness. Based on these findings, EPA revised the PM NAAQS by strengthening the preexisting (1997) standard for "fine" particulate matter 2.5 micrometers or less in diameter (PM2.5) by lowering the allowable daily concentration averaged over 24-hour periods of PM2.5 in the air. The annual PM2.5 standard, which is set in addition to the daily standard to address human health effects from chronic exposures to the pollutants, is unchanged from the 1997 standard. The decision not to tighten the annual standard was reversed by the D.C. Circuit and remanded to EPA for consideration. 

The 2006 particulates NAAQS also retained the 24-hour standard and revoked the annual standard for slightly larger, but still inhalable, particles less than or equal to 10 micrometers (PM10). The EPA abandoned its proposal to replace the particle size indicator of PM10 with a range of 10 to 2.5 micrometers (PM10-2.5). The D.C. Circuit's February 24, 2009, decision upheld EPA's decisions with regard to PM10 NAAQS. 

EPA's ongoing implementation of the 2006 NAAQS, beginning with the designation of those geographical areas not in compliance (typically defined by counties or portions of counties), may become an area of debate among Members of Congress, states, and other stakeholders. Although EPA is not requiring new nonattainment designations for PM10, the tightening of the PM2.5 standard increased the number of areas in nonattainment. On November 13, 2009, EPA published its final designations for the 2006 PM NAAQS that include 120 counties and portions of counties in 18 states as nonattainment areas based on 2006 through 2008 air quality monitoring data. In December of 2008 EPA had announced designation of 211 counties and portions of counties in 25 states as nonattainment areas for the 2006 PM NAAQS based on 2005 through 2007 data.


Date of Report: April 9, 2010
Number of Pages: 27
Order Number: RL34762
Price: $29.95

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