	Introduction

The Environmental Protection Agency (EPA) Administrator signed a proposal to strengthen the National Ambient Air Quality Standard (NAAQS) for particulate matter (PM) on June 14, 2012, intended to address potential health effects (including chronic respiratory disease and premature mortality) associated with short- and long-term exposure to particulate matter. The date of the proposal was per a June 6, 2012, order issued by the U.S. Court of Appeals for the District of Columbia Circuit in response to petitions filed by advocacy groups and 11 states. The June 2012 PM NAAQS proposal is the culmination of EPA's statutorily required review of the NAAQS under the Clean Air Act (CAA) based on studies available through mid-2009 and recommendations of EPA staff and a scientific advisory panel (Clean Air Scientific Advisory Committee, or CASAC ) established by the CAA. The proposal includes options for new secondary standards to address visibility impacts in urban areas associated with PM 2.5 , but would not modify the standards for inhalable coarse particles smaller than 10 microns or PM 10 . As per statutory scheduling requirements under the CAA, the final designation of areas (primarily counties) as nonattainment for any revised PM standards would not be determined until the end of 2014, and states would have until at least 2020 to achieve compliance. Within three years of EPA's final designations of areas, states are required to submit plans (state implementations plans or SIPs) outlining how they will achieve or maintain compliance with the revised primary PM NAAQS. As proposed June 2012, the PM 2.5 and PM 10 standards and other implementation changes would be as follows:
Primary (Public Health) PM Standards
PM 2.5 : strengthen the annual standard, which currently is 15 micrograms per cubic meter (µg/m 3 ), by setting a new limit of 12 µg/m 3 or 13 µg/m 3 ; retain 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. Implementing the Proposed Revised PM2.5 NAAQS

Promulgation of NAAQS sets in motion a process under which the states and EPA first identify geographic nonattainment areas, those areas failing to comply with the NAAQS based on monitoring and analysis of relevant air quality data. These may include new or amended state regulations and new or modified permitting requirements. As shown in the table, estimated benefits are expected to be at least 30 times greater than the costs of $69 million for the most stringent option included in the June 2012 proposal. As mentioned earlier, several states petitioned EPA, and subsequently filed suit in the D.C. Critics of more stringent PM NAAQS contend—
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 cut-off; 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; 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, have not yet been realized, pointing out that based on EPA's trends data that annual and 24-hour measured PM national concentrations have declined 24% and 28% respectively from 2001 to 2010. Although EPA proposed to retain the PM 10 , some stakeholders and Members remain skeptical that the final revised NAAQS could be changed from the proposal. NAAQS decisions have often been a source of significant concern to many in Congress. EPA will likely receive considerable comments in response to the June 2012 proposal. Circuit's decision and a related Consent Agreement, EPA has agreed to issue final revised PM NAAQS by December 14, 2012.
On June 29, 2012, the Environmental Protection Agency (EPA) published a proposal to revise the National Ambient Air Quality Standard (NAAQS) under the Clean Air Act (CAA) for particulate matter (PM), in response to a June 6, 2012, order issued by the U.S. Court of Appeals for the District of Columbia Circuit. Environmental and public health advocacy groups and 11 states had petitioned the agency, and subsequently filed suit in the D.C. Circuit alleging that EPA failed to perform its mandated duty to complete the review of the PM NAAQS within the statutory deadline. EPA has agreed to issue final revised PM NAAQS by December 14, 2012. EPA's review of the PM NAAQS has generated considerable debate and oversight in Congress.
The June 2012 proposal would strengthen 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 range of 12 to 13 µg/m.3 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 would be retained, as would the existing standards for larger, but still inhalable "coarse" particles less than 10 micrometers in diameter or PM10. "Secondary" standards that provide protection against "welfare" (non-health) effects, such as ecological effects and material deterioration, would be identical to the primary standards the same as in 2006, but the June 2012 proposal included two options for a 24-hour PM2.5 standard to improve visibility.
In developing the June 2012 proposal, EPA reviewed scientific studies available since the agency's previous review in 2006. EPA determined, and the independent scientific advisory committee mandated under the CAA (Clean Air Scientific Advisory Committee, or CASAC) concurred, that evidence continues to show associations between particulates in ambient air and numerous significant health problems, including aggravated asthma, chronic bronchitis, non-fatal 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 expects that the potential benefits of the proposed revisions would range from an estimated low of $88.0 million to a high of $5.9 billion dependent on the concentration level and other factors, and estimated costs would range from $2.9 million to $69.0 million. Some stakeholders and some Members express concerns that the cost impacts will be more significant than EPA estimated in those areas unable to comply with the new standards. EPA's establishment of or 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.
Final revised PM NAAQS will start 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 the determination of "nonattainment" areas (primarily counties) based on multiple years of monitoring data and other factors submitted by the states, state and local governments must develop (or revise) State Implementation Plans (SIPs) outlining measures to attain the standard. These often involve promulgation of new regulations by states, leading to the issuance of revised air permits. The process typically takes several years. Based on statutory scheduling requirements, designation of areas as nonattainment for any revised PM NAAQS would not be determined until the end of 2014, and states would have until at least 2020 to achieve compliance.