2006 National Ambient Air Quality Standards (NAAQS) for Fine Particulate Matter (PM2.5): Designating Nonattainment Areas

Robert Esworthy
Specialist in Environmental Policy

The Environmental Protection Agency (EPA) published its final revisions to the National Ambient Air Quality Standards (NAAQS) for particulate matter (particulates, or PM) on October 17, 2006. EPA's actions leading up to and following promulgation of the 2006 standard have been the subject of considerable congressional oversight. EPA's ongoing implementation of the standard, beginning with the designation of those geographical areas not in compliance, will likewise be an area of concern and debate among many Members of Congress, states, and other stakeholders for some time. 

Promulgation of NAAQS sets in motion a process under which the states and the EPA identify areas that exceed the standard ("nonattainment areas") using multi-year air quality monitoring data and other criteria, requiring states to take steps to reduce pollutant concentrations in order to achieve it. 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. The final designations, which include tribal land of 22 tribes, were effective as of December 14, 2009. States have three years from the effective date to submit State Implementation Plans (SIPs), which identify specific regulations and emission control requirements that would bring an area into compliance. 

In December of 2008 EPA had identified 211 counties and portions of counties (58 areas) in 25 states for designation as nonattainment for the 2006 PM NAAQS based on 2005 through 2007 data. The publication of these designations—and thus the effective date of the final designations—was delayed pending review by the current Administration. The review was initiated, in part, in response to a White House January 20, 2009, memorandum regarding regulatory review. This review and the availability of more current air quality monitoring data resulted in the final designations published in November 2009. 

The 2006 NAAQS strengthened 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 daily standard averaged over 24-hour periods is reduced from 65 micrograms per cubic meter (μg/m3) to 35 μg/m3. However, the annual PM2.5 standard, which addresses human health effects from chronic exposures to the pollutants, is unchanged from the 1997 standard of 15 μg/m3. The 2006 NAAQS did not substantially modify the daily standard for slightly larger, but still inhalable, particles less than or equal to 10 micrometers (PM10), retaining the 24-hour standard but revoking the annual standard for PM10. 

EPA's final nonattainment designations are only for the revised 2006 24-hour PM2.5 standard. The EPA did not require new nonattainment designations for PM10. The final designations for the 2006 PM2.5 NAAQS include a few areas designated nonattainment for PM2.5 for the first time, but, as expected, the majority of the counties identified overlap with EPA's final nonattainment designations for the 1997 PM2.5 NAAQS. EPA's designations for the 1997 PM2.5 NAAQS included all or part of 204 counties in 20 states and the District of Columbia. Most of them were only exceeding the annual standard; only 12 counties were exceeding both the 24-hour and the annual standards. Thus, the 2006 tightening of the 24-hour standard resulted in an increased number of areas being designated nonattainment based on exceedances of both the 24-hour and the annual standards. .


Date of Report: February 25, 2010
Number of Pages: 37
Order Number: R40096
Price: $29.95

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