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, 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's review of and revisions to the PM NAAQS has 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 ( g/m3) to a limit of 12 g/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 g/m3 to 35 g/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. "Secondary" standards that provide protection against "welfare" (non-health) effects, such as ecological effects and material deterioration, are identical to the primary standards and the same as in 2006. The proposed rule published June 29, 2012, solicited comments on two options for a 24-hour PM2.5 standard to improve visibility that were not adopted in the final rule. 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 often involve promulgation of new regulations by states, and the issuance of revised air permits. The process typically takes several years. Based on statutory scheduling requirements, nonattainment designations for revised PM NAAQS would not be determined until the end of 2014, and states would have until at least 2020 to achieve compliance with the January 2013 revised PM2.5 NAAQS."