	Introduction

National Ambient Air Quality Standards (NAAQS) are a core component of the Clean Air Act (CAA). The EPA and states are in the process of finalizing the implementation of the NAAQS for particulates promulgated in 1997, delayed because of court challenges and other factors. The EPA's 1997 revisions to the particulate matter standards (also referred to as the particulates NAAQS) included separate requirements for PM 2.5 for the first time. EPA's and states' experiences following the promulgation of the PM 2.5 NAAQS 13 years ago could provide relevant insights as EPA and states encounter issues in the initial stages of implementing the PM 2.5 NAAQS as revised in October 2006 and as the agency proceeds with its current review of the particulates NAAQS. States were required to submit, by April 2008, their State Implementation Plans (SIPs) for how the designated nonattainment areas will meet the 1997 PM 2.5 NAAQS. States with nonattainment areas were to be in compliance with the 1997 PM 2.5 NAAQS by April 5, 2010, unless they are granted an extension. In a July 11, 2008, decision ( North Carolina v. EPA ), the U.S. Court of Appeals for the D.C. On August 2, 2010, EPA published a proposed "Transport Rule" intended to supersede the current CAIR. EPA's next round of the periodic review of the particulates NAAQS is under way. EPA has targeted proposing any changes to the standards by February 2011, and October 2011 for final standards. By the end of August 2008, final nonattainment designations were in effect for 39 areas, comprising 205 counties within 20 states (and the District of Columbia) nationwide, with a combined population of almost 90 million. Demonstrating Attainment with the 1997 PM2.5 NAAQS

As noted earlier in this report, several areas previously designated nonattainment for the 1997 PM 2.5 NAAQS currently have air quality that attains the level set by the standards based on certified ambient air monitoring data for the period 2006-2008. SIPs include pollution control measures that are to be implemented by federal, state, and local governments, and rely on models of the impact on air quality of projected emission reductions to demonstrate attainment. On November 27, 2009, EPA published its findings that three states failed to meet the deadline for submitting complete SIPs (74 Federal Register 62251-62255). For the remaining designated areas, states either submitted a complete SIP or EPA made a final approval that the area attained the 1997 PM 2.5 NAAQS based on 2006-2008 air quality data. Recent Actions and Their Implications for Achieving Attainment of the 1997 PM2.5 NAAQS

A number of events, most notably the D.C. Circuit's Decision Vacating the Clean Air Interstate Rule (CAIR)97

The EPA's Rule to Reduce Interstate Transport of Fine Particulate Matter and Ozone, or the Clean Air Interstate Rule (CAIR), published in May 2005, was identified as an important tool for helping states address the interstate transport of pollutants (SO 2 and NOx) from electric generating units (EGUs) hindering downwind states from attaining the eight-hour ozone and 1997 PM 2.5 NAAQS. States and local governments will be required to develop and implement new plans (SIPs) for addressing emissions in those areas that do not meet new standards. Circuit court decision regarding the 2006 particulates NAAQS. However, the court's subsequent December 23, 2008, ruling temporarily reinstating CAIR until EPA promulgates a replacement rule, allowed implementation of the 1997 PM 2.5 NAAQS to continue in the interim.
Particulate matter (PM), including fine particulate matter (PM2.5) and larger, but still inhalable particles (PM10), 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). EPA most recently revised the particulates NAAQS in October 2006, but is due to propose revised standards in February 2011 and promulgate them by October 2011.While currently much of the interest in the particulates NAAQS is focused on reviewing the NAAQS and speculation as to the degree of stringency of any new standards, implementing revised standards can take many years. EPA and states are in the early stages of implementing the 2006 revised standards, and have not finalized implementation of the standards promulgated in 1997 after years of litigation and other delays. This report outlines the implementation process for the 1997 PM2.5 NAAQS and describes issues raised as EPA and states developed and employed implementation strategies for achieving attainment.
The EPA's final designation of 39 areas, consisting of 205 counties in 20 states and the District of Columbia, as "nonattainment" (out of compliance) areas for the 1997 PM2.5 NAAQS became effective in April 2005. A combined population of almost 90 million resides in these areas. States with 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. States were required to submit SIPs for the 1997 PM2.5 NAAQS by April 2008, but EPA did not begin receiving most submissions until July 2008. On November 27, 2009, EPA published its findings that three states failed to meet the deadline for submitting complete SIPs. For the remaining designated areas, states either submitted a complete SIP or EPA made a final approval that the area attained the 1997 PM2.5 NAAQS based on 2006-2008 air quality data. States must be in compliance by 2010, unless they are granted an extension.
A number of issues will continue to be debated as the implementation of the 1997 PM2.5 NAAQS progresses. Notably, the U.S. Court of Appeals for the D.C. Circuit's July 11, 2008, decision (North Carolina v. EPA) to vacate the Clean Air Interstate Rule (CAIR) introduced new concerns and disruptions with respect to the implementation of the 1997 PM2.5 NAAQS. Implementation of CAIR would have assisted states in addressing the interstate transport (upwind state) emission contributions in achieving attainment. The court's December 23, 2008, modified decision allows CAIR to remain in effect, but only temporarily until EPA promulgates a replacement rule, which could have future implications for implementing the PM2.5 NAAQS. On August 2, 2010, EPA published a proposed "Transport Rule" intended to supersede the current CAIR. In addition, other promulgated and proposed EPA rulemakings that influence various aspects of regulating air quality, including EPA's 2006 changes to the particulates NAAQS, continue to impact the 1997 PM2.5 NAAQS implementation process.
EPA and states have encountered similar issues in implementing the 2006 revised particulates NAAQS. Whatever the outcome of the current review of the particulates NAAQS, implementation of any changes to the standards in many regards will also likely mirror the experience of EPA and states following the promulgation of the PM2.5 NAAQS 13 years ago.