On October 17, 2006, EPA published its revisions to the NAAQS for particulates to provide protection against potential health effects associated with short- and long-term exposure to particulate matter (including chronic respiratory disease and premature mortality). Specifically, the agency lowered the allowable daily concentration averaged over 24-hour periods of PM 2.5 in the air from 65 micrograms per cubic meter (µg/m 3 ) to 35 µg/m 3 . The annual PM 2.5 standard, which is set in addition to the daily standard to address human health effects from chronic exposures to the pollutants, was unchanged. 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 (PM 10 ). While the 2006 particulates NAAQS generally tightened the air quality standards for fine particulate matter, the action caused considerable controversy, including concerns that the standards were outside the range recommended by both EPA staff and by the scientific advisory panel (Clean Air Scientific Advisory Committee, or CASAC ) established by the CAA. Although implementation of the 2006 PM NAAQS continues, EPA initiated its statutorily required review of the PM NAAQS, in part in response to the decision, not long after the 2006 promulgation of the PM NAAQS. The range of issues raised prior to and shortly after the promulgation of the 2006 PM 2.5 NAAQS could provide relevant insights as EPA proceeds with finalizing its decisions with regard to revising particulates NAAQS. The 2006 tightening of the PM 2.5 standards resulted in an increase in the number of areas (typically defined by counties or portions of counties) designated nonattainment. The designations, based on 2006 through 2008 air quality monitoring data, included a few counties that were designated nonattainment for PM 2.5 for the first time, but the majority of the counties identified overlapped with EPA's final nonattainment designations for the 1997 PM 2.5 NAAQS. Circuit. The D.C. Circuit's February 24, 2009, Decision68

In December 2006, a diverse mix of petitioners, including states and state agencies, environmental and public health advocacy organizations, and groups representing various industry and agriculture interests, petitioned the U.S. Court of Appeals for the D.C. Although aspects of the 2006 PM standard remanded to EPA for reconsideration by the court remain in effect and EPA's tightening of the 24-hour PM 2.5 standard was not affected, EPA's completion of its next round of periodic review and June 2012 proposed revisions to the PM standards has generated concerns with respect to the implementation process for the 2006 standards. Petitions from several states and state agencies, as well as the American Lung Association, Environmental Defense, and the National Parks Conservation Association, challenged EPA's decision not to strengthen the primary annual NAAQS standard for PM 2.5 (15µg/m 3 ). In its February 24, 2009, decision, the court granted this part of the petition and remanded the standard to EPA for reconsideration, but did not vacate the standard. For attainment of the 2006 standards (15/35 µg/m 3 ), EPA estimated 1,200 to 13,000 fewer premature deaths based on the expert elicitation. As a result, the D.C. Circuit's February 2009 decision regarding challenges to the 2006 PM NAAQS, delays in implementing the 2006 PM 2.5 NAAQS resulting from the Administration's review of the final designations, and EPA's next round of periodic review of the particulate NAAQS and subsequent June 2012 proposal to revise the standards, have prompted renewed interest in several of the issues associated with the promulgation of the 2006 PM NAAQS discussed throughout this report.
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 but did not specifically vacate the 2006 PM standards. EPA initiated its next round of the periodic review of the PM NAAQS, in part, in response to the court's decision and on June 29, 2012, published a proposal to strengthen the standards. 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 particulates NAAQS established in 2006 were 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.