Particulate Matter (PM2.5): Implementation of the 1997 National Ambient Air Quality Standards (NAAQS)

Robert Esworthy
Specialist in Environmental Policy

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). Primary NAAQS are designed to protect human health, with an adequate margin of safety. After years of litigation and other delays, EPA is implementing the NAAQS for PM2.5 promulgated in 1997. This report outlines the implementation process for the 1997 PM2.5 NAAQS and describes issues raised as EPA and states develop implementation strategies. 

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. Although its decision was modified on December 23, 2008, 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 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. EPA has projected July 2010 for proposing a replacement rule. 

In addition, other promulgated and proposed EPA rulemakings that influence various aspects of regulating air quality, including EPA's changes to the particulates NAAQS, could affect the 1997 PM2.5 NAAQS implementation process. As required under the CAA, EPA reviewed the PM2.5 and PM10 NAAQS, and on October 17, 2006, promulgated final revisions that included a strengthening of the 1997 PM2.5 standards. On November 13, 2009, EPA published its final designations for the 2006 PM2.5 NAAQS that include 120 counties and portions of counties in 18 states as nonattainment areas. EPA has initiated the next round of the periodic review of the particulates NAAQS and announced its intention to accelerate that review. 

As implementation of the 1997 NAAQS moves forward, its effects on states and tribes will be a continuing issue of interest to Congress. Although EPA has reported that 19 of the 39 nonattainment areas are currently meeting the 1997 PM2.5 standard according to the most recent air monitoring data, many questions and concerns remain. These include, for example, whether special provisions can be made for meeting attainment deadlines for areas affected by upwind pollution, and what impact the implementation of the 2006 particulates NAAQS will have.


Date of Report: April 16, 2010
Number of Pages: 32
Order Number: RL32431
Price: $29.95

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