Air Quality: EPA's 2006 Changes to the Particulate Matter (PM) Standard


Publication Date: May 2007

Publisher: Library of Congress. Congressional Research Service


Research Area: Environment



On October 17, 2006, the EPA published its final revisions to the National Ambient Air Quality Standards (NAAQS) for particulate matter (particulates, or PM). The EPA reviewed more than 2,000 scientific studies and found that the evidence continued to support associations between exposure to particulates in ambient air and numerous significant health problems, including aggravated asthma, chronic bronchitis, reduced lung function, heart attacks, and premature death in people with heart or lung disease. Based on several analytical approaches, the EPA estimated that compliance with the new 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. Although a tightening of the standards, the new particulates NAAQS are not as stringent as recommended by EPA staff or the independent scientific advisory committee (Clean Air Scientific Advisory Committee, or CASAC) mandated under the Clean Air Act.

The new particulates NAAQS strengthen the pre-existing (1997) standard for "fine" particulate matter 2.5 micrometers or less in diameter (PM2.5) by lowering the allowable daily concentration of PM2.5 in the air. The new daily standard averaged over 24-hour periods is reduced from 65 micrograms per cubic meter (µg/m3) to 35 µ g/m3. However, 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 of 15 µg/m3, although the CASAC had recommended a tighter annual standard in the range of 13 to 14 µg/m3. Eighty-eight million people live in the 208 counties designated as "nonattainment" areas for the 1997 PM2.5 NAAQS.

The new 2006 particulates NAAQS also retain the 24-hour standard and revoke 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), and did not follow through on its proposal to exclude any mix of particles "dominated by rural windblown dust and soils and PM generated by agricultural and mining sources."

In addition to the divergence from the CASAC's recommendation, several elements of the new 2006 particulates NAAQS may prove controversial, 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. In late December 2006, several states and industry, agriculture, business, and public advocacy groups petitioned the D.C. Circuit Court of Appeals to review the new 2006 particulates NAAQS. The establishment of particulates NAAQS in 1997 proved controversial and included extensive congressional oversight. Congress may conduct oversight of the new 2006 particulates NAAQS, given the potential public health and economic impacts.