Cover title. "Order Code RL32431." "Updated January 30, 2006." Includes bibliographical references.

Particulate matter (PM), including fine particulate matter (PM2.5), is one of the six principal pollutants for which the U.S. Environmental Protection Agency (EPA) has set National Ambient Air Quality Standards (NAAQS) under the Clean Air Act (CAA). NAAQS are designed to protect human health within an adequate margin of safety. After several years of litigation and other delays, EPA is moving to implement the NAAQS for PM2.5 promulgated in 1997. This report, which will be updated as developments warrant, provides information on the designation process for PM2.5 "attainment" and "nonattainment" areas. It also discusses issues that have been raised as EPA, the states, and nonattainment areas develop implementation strategies. On April 14, 2005, EPA published a final rule amending designated geographical areas for PM2.5 standards, which were originally published in January 2005. The Agency's amendments were based on a review of supplemental 2004 air monitoring data submitted by several states. As a result, 39 areas, consisting of 208 counties in 20 states and the District of Columbia, were designated as nonattainment areas PM2.5 nonattainment areas are required to develop comprehensive implementation plans, referred to as State Implementation Plans (SIPs), demonstrating how attainment will be reached by a designated deadline. SIPs include pollution control measures that rely on models of the impact on air quality of projected emission reductions to demonstrate attainment. EPA published a proposed "PM2.5 implementation" rule November 1, 2005, that provides guidance and procedures for establishing controls to achieve and maintain attainment. A number of issues will continue to be debated as the implementation of the PM2.5 NAAQS progresses. Some areas that have not been designated as nonattainment under implementation of other NAAQS have been designated "nonattainment" for the first time. Questions and concerns include the following: what criteria were used to determine nonattainment; whether special provisions can be made for meeting attainment deadlines, particularly for areas affected by upwind pollution; what grants or other funding might be available to help areas reach attainment; and how nonattainment designation might affect economic development and transportation investments in an area. Legislation and EPA rulemaking that affect aspects of regulating air quality could influence the implementation process. Court challenges that followed the release of the eight-hour ozone designations, and EPA's ongoing mandated periodic review of PM NAAQS, could also affect PM2.5 NAAQS implementation. An EPA staff paper released in September 2005 as part of the periodic review recommended that the Agency consider more stringent PM standards.