Additionally, EPA established separate standards for two categories of PM based on size: "fine" particulate matter 2.5 micrometers or less in diameter (referred to as PM 2.5 ) and slightly larger, but still inhalable, particles less than or equal to 10 micrometers (referred to as PM 10 ). EPA last reviewed and revised the PM NAAQS in 2006. Promulgation of NAAQS sets in motion a process under which the states and EPA first identify geographic nonattainment areas (i.e., those areas failing to meet the NAAQS) based on monitoring and analysis of relevant air quality data. The April 2015 modifications did not impact EPA's designation determinations for areas in Indian country as published in January 2015. However, in a January 4, 2013, decision, the U.S. Court of Appeals for the District of Columbia Circuit determined that EPA had erred in implementing the PM 2.5 NAAQS under Subpart 1 and required the agency to implement the PM 2.5 NAAQS under Subpart 4 of Part D in Title I of the CAA ("Subpart 4"). 7407) of the CAA requires the governor of each state to submit a list to EPA of all areas in the state "designating as ... nonattainment, any area that does not meet ( or that contributes to ambient air quality in a nearby area that does not meet ) an air quality standard" (emphasis added). EPA April 2015 Amended Final Designations

The final area designations as amended and published in the April 2015 Federal Register encompass 20 counties or portions of counties (nine areas) in four states—California, Idaho, Ohio, and Pennsylvania—as nonattainment only for the 2013 revised annual PM 2.5 standard. The area in Indiana (2 counties) and one of the two areas in Kentucky (2 of the 5 counties) were re-designated unclassifiable. EPA also designated five areas in Georgia (including two counties in Alabama and South Carolina) as unclassifiable. Several of the 14 nonattainment areas included counties from multiple states. Comparing EPA's Final Nonattainment Designations for the 2013 PM NAAQS with the 2006 and 1997 PM2.5 NAAQS Final Designations

EPA's final designations for nonattainment of the 2006 and 1997 PM 2.5 NAAQS (those areas with or contributing to air quality levels exceeding the annual and 24-hour PM 2.5 standards or both) included all or part of 242 counties in 28 states and the District of Columbia. Conclusion

States will have 18 months from April 15, 2015, the effective date of EPA's final designations for the 2013 PM 2.5 NAAQS, to submit SIPs, which identify specific regulations and emission control requirements that are to bring an area into compliance. Under CAA, Section 188 of Subpart 4, states must achieve attainment as expeditiously as practicable but no later than the end of the sixth calendar year after designation as nonattainment: December 2021 for the 2013 PM 2.5 standard. Some Members expressed concerns in hearings, letters to the EPA administrator, and proposed legislation in anticipation of potential changes to the PM NAAQS leading up to the January 2013 final published revisions. Counties in Nonattainment for the 2013 PM 2.5 NAAQS Annual (12 μg/m 3 ): U.S. EPA January 15, 2015, Final Designations and Comparison with the 2006 and 1997 PM 2.5 NAAQS Final Designations
The following maps present EPA's final nonattainment area designations as published in the Federal Register on January 15, 2015, which EPA subsequently amended April 7, 2015, based on more current air quality data (2012-2014).
On April 7, 2015, the Environmental Protection Agency (EPA) published amendments to the January 15, 2015, final rule designating areas for compliance with the 2013 primary annual National Ambient Air Quality Standard (NAAQS) for fine particulate matter (PM2.5). Revising a NAAQS established under the Clean Air Act (CAA) sets in motion a process under which the states and 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 meet the standard.
The 2013 revisions to the PM NAAQS were the subject of considerable congressional oversight. EPA's designation of nonattainment areas may be an issue of interest and debate among Members of Congress, states, and other stakeholders. The PM NAAQS revisions, published January 2013 changed the annual health-based ("primary") standard for "fine" particulate matter 2.5 micrometers or less in diameter (or PM2.5) to a limit of 12 micrograms per cubic meter (µg/m3) from the 15 µg/m3 limit. Revisions to the PM NAAQS retained the existing 24-hour primary standard for PM2.5 of 35 µg/m3 (as promulgated in 2006) and the existing standard for larger, but still inhalable, "coarse" particles 10 micrometers or less in diameter, or PM10.
During EPA's consideration of alternative approaches for revising the PM NAAQS, many stakeholders and some in Congress expressed concern about the potential impacts associated with an increased number of areas that may be deemed nonattainment under a more stringent standard. The number of areas ultimately determined nonattainment for the revised PM NAAQS were considerably fewer than some had anticipated.
Based on its review of recently submitted 2014 air quality data, EPA's April 2015 modifications to the final area designations for the 2013 PM NAAQS resulted in nine areas consisting of 20 counties in four states designated as nonattainment. All but two of the 20 counties have been previously designated as nonattainment for the 2006 and/or the 1997 PM2.5 NAAQS. In accordance with a decision by the U.S. Court of Appeals for the District of Columbia Circuit on January 4, 2013, EPA classified all areas determined to be in nonattainment as "moderate" nonattainment areas under the authority of Section 188 of the CAA.
In comparison to the nonattainment area designations as amended by EPA in April 2015, EPA's final designations published in January 2015 were composed of 14 areas comprising 38 counties in 6 states. The EPA April 2015 amended designations changed the nonattainment designation of two areas in Pennsylvania (four counties) and one each in Ohio (three counties) and Ohio (four counties)/Kentucky (three counties) to "unclassifiable/attainment" and one area in Kentucky (two counties)/Indiana (two counties) to "unclassifiable." EPA also designated five areas in Georgia (including two counties in Alabama and South Carolina) as unclassifiable.
States have 18 months from the April 15, 2015, effective date of EPA's final designations to submit State Implementation Plans, which identify specific regulations and emission control requirements intended to bring an area into compliance or maintain compliance. Section 188 of the CAA requires that moderate nonattainment areas achieve attainment as expeditiously as practicable but no later than the end of the sixth calendar year after designation as nonattainment.