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Friday, October 28, 2011

The National Ambient Air Quality Standards (NAAQS) for Particulate Matter (PM): EPA’s 2006 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 U.S. Court of Appeals for the District of Columbia Circuit, challenging certain aspects of EPA’s revisions. A February 24, 2009, decision by the D.C. 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 initiated its next round of the periodic review of the particulates NAAQS, in part, in response to the court’s decision, and plans to propose its decision regarding changes to the PM standards sometime during the fall of 2011. These actions, and the ongoing implementation of the 2006 PM NAAQS, have prompted renewed interest among Members of Congress.

Experiences and issues leading up to and following the promulgation of the 2006 PM2.5 NAAQS could provide relevant insights as EPA proceeds with its current review. 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.

EPA found that the evidence continued to support associations between exposure to particulates in ambient air and numerous health problems. Based on several analytical approaches, EPA estimated that compliance with the revised NAAQS would prevent 1,200 to 13,000 premature deaths annually, as well as substantial numbers of hospital admissions and missed work days due to illness. EPA revised the PM NAAQS by strengthening the 1997 standard for “fine” particulate matter 2.5 micrometers or less in diameter (PM2.5). Specifically, the agency lowered the allowable daily concentration averaged over 24-hour periods of PM2.5 in the air from 65 micrograms per cubic meter (μg/m3) to 35 (μg/m3). 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, was unchanged from the 1997 standard. The decision not to tighten the annual standard was overturned 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). 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, including EPA’s November 13, 2009, final designation of those geographical areas not in compliance (typically defined by counties or portions of counties), has been an area of debate among some Members of Congress, states, and other stakeholders. Although EPA did not require new nonattainment designations for PM10, the tightening of the PM2.5 standard resulted in an increased number of areas in nonattainment compared to the designations for the 1997 PM NAAQS. EPA’s November 2009 final designations for the 2006 PM NAAQS included 120 counties and portions of counties in 18 states as nonattainment areas based on 2006 through 2008 air quality monitoring data.



Date of Report: October 17, 2011
Number of Pages: 31
Order Number: RL34762
Price: $29.95

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