	Introduction

On January 15, 2013, the Environmental Protection Agency (EPA) published a final rule in the Federal Register to strengthen the National Ambient Air Quality Standard (NAAQS) for particulate matter (PM) . The standards, set pursuant to the Clean Air Act (CAA), address potential health e ffects (including chronic respiratory disease and premature mortality) associated with short- and long-term exposure to particulate matter. In the final rule, the "secondary" standards that provide protection against "welfare" (nonhealth) effects, such as ecological effects and material deterioration, are identical to the primary standards, the same as in 2006. On January 15, 2015, EPA published its classification of 14 areas as "Moderate" nonattainment for the revised 2013 primary annual PM 2.5 standard. CAA section 188(c)(1) of Subpart 4 requires Moderate areas achieve attainment as expeditiously as practicable, but no later than the end of the sixth year after the effective date of final designation as nonattainment. Following this designation, approved by EPA, states then develop a SIP, which consists essentially of state regulations to be implemented by states that would affect the state emissions inventory, and therefore the expected or modeled concentrations of air pollutants. In the final rule published by EPA on January 15, 2013, the PM 2.5 and PM 10 standards and other implementation changes are as follows:
Primary (Public Health) PM Standards
PM 2.5 : EPA revised the annual standard, which currently is 15 micrograms per cubic meter (µg/m 3 ), by setting a new limit of 12 µg/m 3 (the proposal included an optional limit of 13 µg/m 3 and solicited comment for 11 µg/m 3 ); compliance with the "annual" standard is determined by whether the three-year average of its annual average PM 2.5 concentration (at each monitoring site in the area) is less than or equal to 12 µg/m 3 ; as proposed, EPA retained the daily (24-hour) standard at 35 µg/m 3 based on the current three-year average of the 98 th percentile of 24-hour PM 2.5 concentrations as established in 2006. EPA also revised its Regulatory Impact Analysis (RIA), in large part in response to comments received. EPA's 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. Rather it starts a process that could result in significant required investments by emitting sources in control measures. In part in response to comments received and considered following the June 2012 proposal, EPA revised its RIA for the final rule. As shown in Table 2 , EPA estimated that the monetized benefits associated with the January 2013 final revised PM 2.5 annual standard of 12 µg/m 3 would range $4.0 billion to $9.1 billion per year in 2020 (2010 $), compared to annual costs ranging from $53.0 million to $350.0 million. Critics of more stringent PM NAAQS stress that
more stringent (and in some cases the existing) standards are not justified by the scientific evidence; the proposal does not take into account studies completed since the 2009 cutoff; requiring the same level of stringency for all fine particles without distinguishing sources is unfounded; costs and adverse impacts on regions and sectors of the economy are excessive; EPA has potentially overstated the expected benefits and underestimated expected costs; revising the standards could impede implementation of the existing (2006) PM NAAQS and the process of bringing areas into compliance, given the current status of this process; the benefits (and costs) associated with implementation of the 2006 PM NAAQS, as well as compliance with other relatively recent EPA air quality regulations that are being implemented, have not yet been realized; and revisions to PM NAAQS are unnecessary as shown by EPA's trends data that annual and 24-hour measured PM national concentrations have declined 24% and 28% respectively from 2001 to 2010. For details regarding EPA's initial final designations for the 2013 PM NAAQS revisions published January 15, 2015, and the subsequent April 7, 2015, modified designations, see CRS Report R43953, 2013 National Ambient Air Quality Standard (NAAQS) for Fine Particulate Matter (PM2.5): Designating Nonattainment Areas , by [author name scrubbed].
On January 15, 2013, the Environmental Protection Agency (EPA) published a final rule revising the National Ambient Air Quality Standard (NAAQS) for particulate matter (PM). The revised air quality standards were completed pursuant to the Clean Air Act (CAA) and, in part, in response to a court order and consent agreement. Based on its review of scientific studies available since the agency's previous review in 2006, EPA determined that evidence continued to show associations between particulates in ambient air and numerous significant health problems, including aggravated asthma, chronic bronchitis, nonfatal heart attacks, and premature death. Populations shown to be most at risk include children, older adults, and those with heart and lung disease, and those of lower socioeconomic status. EPA's review of and revisions to the PM NAAQS have generated considerable debate and oversight in Congress.
The January 2013 revisions change the existing (2006) annual health-based ("primary") standard for "fine" particulate matter 2.5 micrometers or less in diameter (or PM2.5), lowering the allowable average concentration of PM2.5 in the air from the current level of 15 micrograms per cubic meter (µg/m3) to a limit of 12 µg/m3. The annual PM2.5 NAAQS is set so as to address human health effects from chronic exposures to the pollutants. The existing "24-hour primary standard" for PM2.5 that was reduced from 65 µg/m3 to 35 µg/m3 in 2006 was retained, as was the existing standard for larger, but still inhalable, "coarse" particles less than 10 micrometers in diameter, or PM10. As it did in 2006, EPA set "secondary" standards that provide protection against "welfare" (nonhealth) effects, such as ecological effects and material deterioration, identical to the primary standards.
EPA revised the Regulatory Impact Analysis (RIA) accompanying its June 2012 proposed rule in part in response to comments received regarding the agency's cost and benefit estimates. In its December 2012 RIA, EPA estimated that the potential "quantifiable" health benefits (2010 $) associated with attaining the PM standard would range from $4.0 billion to $9.1 billion, and costs (2010 $) would range from $53.0 million to $353.0 million. Some stakeholders and some Members continue to express concerns that cost impacts would be more significant than those estimated by EPA for those areas out of compliance with the new standards.
EPA's revisions to the PM NAAQS do not directly regulate emissions from specific sources, or compel installation of any pollution control equipment or measures, but indirectly could affect operations at industrial facilities and other sources throughout the United States. Revising PM NAAQS starts a process that includes a determination of areas in each state that exceed the standard and must, therefore, reduce pollutant concentrations to achieve it. Following determinations of these "nonattainment" areas based on multiple years of monitoring data and other factors, state and local governments must develop (or revise) State Implementation Plans (SIPs) outlining measures to attain the standard. These include promulgation of new regulations by states, and the issuance of revised air permits. The process typically takes several years.
On January 15, 2015, EPA published its classification of 14 areas as "Moderate" nonattainment for the revised 2013 primary annual PM2.5 standard. EPA subsequently published amended designations on April 7, 2015. 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. For a Moderate area, CAA Section 188(c)(1) of Subpart 4 establishes an attainment deadline of as expeditiously as practicable but no later than the end of the sixth calendar year after designation as nonattainment.