On October 17, 2006, EPA published its revisions to the NAAQS for particulate matter (PM) to provide protection against potential health effects associated with short- and long-term exposure to particulates (including chronic respiratory disease and premature mortality). The standard for slightly larger, but still inhalable, particles less than or equal to 10 micrometers (PM 10 ) established in 1987 was not similarly changed. Promulgation of NAAQS sets in motion a process under which the states and EPA first identify geographic nonattainment areas, those areas failing to meet the NAAQS based on monitoring and analysis of relevant air quality data. States then have three years from the date of EPA's final designations to submit nonattainment area State Implementation Plans (SIPs), which identify specific regulations and emission control requirements that will bring an area into compliance. The publication of final designations—and thus the effective date of the final designations—had been delayed since January 2009 pending review by the incoming Administration. The January 2013 revisions changed the existing (2006) annual health-based ("primary") standard for "fine" particulate matter 2.5 micrometers or less in diameter (or PM 2.5 ), lowering the allowable average concentration of PM 2.5 in the air from the current level of 15 micrograms per cubic meter (µg/m 3 ) to a limit of 12 µg/m 3 . EPA did not require new nonattainment designations for PM 10 based on the 2006 revisions to the standard. EPA's November 2009 final designations, which were based on air quality monitoring data for calendar years 2006 through 2008, do not include counties violating the annual standard, as the level is unchanged from the 1997 PM 2.5 NAAQS. Comparing the 2006 and 1997 PM2.5 NAAQS Designations

EPA's final designations for nonattainment of the 1997 PM 2.5 NAAQS (those areas with or contributing to air quality levels exceeding the annual and 24-hour standards or both) included all or part of 204 counties in 20 states and the District of Columbia. Based on the final designations for the 2006 24-hour PM 2.5 NAAQS, 38 counties would be designated nonattainment for PM 2.5 for the first time but the majority of the counties identified overlap with EPA's final nonattainment designations for the 1997 PM 2.5 NAAQS. Most of the 1997 PM 2.5 nonattainment areas were only exceeding the annual standard; only 12 counties were exceeding both the 24-hour and the annual standards. Thus, tightening the 24-hour standard resulted in an increased number of areas (82 counties) being designated nonattainment based on exceedances of both the 24-hour and the annual standard. Conclusions

The designation of geographical areas unable to meet the NAAQS is a critical step in NAAQS implementation, and historically has been an issue of concern and debate among EPA, states and tribes, various stakeholders, and some Members of Congress. Although EPA and states continue the implementation of the 2006 revised PM 2.5 standards, the EPA recently completed the next round of periodic review of the particulates NAAQS, and on January 15, 2013, EPA published a final rule further revising the PM 2.5 standards. Comparison of EPA's Final and Interim Nonattainment Designation Areas for the 2006 24-Hour PM 2.5 NAAQS and the Final Nonattainment Designation Areas for the 1997 PM 2.5 NAAQS
Appendix C. Tribal Lands: U.S. EPA Designations for the 2006 PM 2.5 NAAQS 24-Hour Standard
Appendix D. Map Depicting Counties in Nonattainment for the 2006 24-Hour PM 2.5 NAAQS: EPA's Designation as of December 22, 2008
On December 22, 2008, EPA had identified 58 areas in 25 states, comprising 211 counties (154 counties and portions of 57 additional counties) for designation as nonattainment for the revised 2006 24-hour PM 2.5 standard.
The Environmental Protection Agency (EPA) published revisions to the Clean Air Act (CAA) 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 and states' ongoing implementation of the standard, beginning with the designation of those geographical areas not in compliance, likewise has been an area of concern and debate among some Members of Congress, states, and other stakeholders for some time. EPA's most recent round of periodic review of the particulates NAAQS and final rule revising the PM NAAQS, published January 15, 2013, prompted further scrutiny of the ongoing implementation of the standards.
Promulgation of NAAQS sets in motion a process under which the states and EPA identify areas that exceed the national 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. The publication of the final designations for the 2006 NAAQS—and thus the effective date of the final designations—had initially been delayed pending review by the current Administration. On November 13, 2009, EPA published its final designations for the 2006 PM NAAQS that included 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 nonattainment area State Implementation Plans (SIPs), which identify specific regulations and emission control requirements that would bring a nonattainment area into compliance.
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 was 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, was 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. EPA did not require new nonattainment designations for the PM2.5 annual standard and for PM10. The final designations for the 2006 PM2.5 NAAQS included a few areas designated nonattainment for PM2.5 for the first time, but, as expected, the majority of the counties identified overlapped 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.