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Area Designations for 2006 24-Hour Fine Particle (PM2.5) Standards

Fact Sheet — Final Area Designations for the 24-hour Fine Particle Standard Established in 2006


  • On October 8, 2009, the Environmental Protection Agency (EPA) issued final area designations for the 24-hour national air quality standards for fine particulate matter (PM2.5).  EPA has identified areas as either “nonattainment”, “unclassifiable/attainment”, or “unclassifiable”. EPA revised the 24-hour fine particle standards to 35 micrograms per cubic meter (µg/m3) in 2006.
  • Today’s action designates 31 areas, composed of 120 full and partial counties, as “nonattainment areas.”  These areas will need to develop and implement plans to reduce pollution to meet the 24-hour PM2.5 standards. Twenty one Tribes are located within the boundaries of these nonattainment areas.  EPA based the designations on the most recent set of air quality monitoring data from 2006 to 2008 as well as other factors, analytical tools, and technical information.
  • The air monitoring data from 2006 to 2008 also show that 91 counties that previously had been notified that they were violating or contributing to a violation of the standards (based on 2005-2007 air quality data) now meet the standards and will be designated as attainment/unclassifiable.  These areas must prevent their daily fine particle air quality from deteriorating to unhealthy levels.
  • In a related action, EPA will notify governors and tribal leaders in Arizona, California and Texas that 2006-2008 monitoring data show that certain areas in these states have violated one or more of the particulate matter standards. EPA will evaluate these areas to determine appropriate boundaries for the potential nonattainment designations. These include:
    • For the 24-hour PM2.5 standards:
      • Arizona: Pinal County
      • California: Plumas County and Shasta County
    • For the annual PM2.5 standard of 15 µg/m3 (set in 1997):
      • Arizona: Pinal County
      • Texas: Harris County
  • EPA will work closely with the affected state and tribal leaders in evaluating these potential nonattainment areas.  The agency expects to complete the process by early 2010.


  • Nonattainment areas include the counties with monitors that violate a standard and the nearby areas that contribute to that violation. The Clean Air Act requires state, local and tribal governments to take steps to control fine particle pollution in PM2.5 nonattainment areas. Those steps may include stricter controls on industrial facilities and additional planning requirements for transportation-related sources.
  • State and local governments must detail these steps in plans that demonstrate how they will meet the 24-hour PM2.5 standards. Those plans are known as state implementation plans, or SIPs. States must submit their plans to EPA within three years after the effective date of the agency’s final designations provided in the Federal Register.  
  • Tribes also may submit plans, known as tribal implementation plans (TIPS), but are not required to do so. 
  • Nonattainment areas are required to meet the standards by 2014.  EPA may grant attainment date extensions for up to five additional years in areas with more severe PM2.5 problems and where emission control measures are not available or feasible.
  • Nonattainment areas must implement “transportation conformity,” which requires that local transportation and air quality officials coordinate planning to ensure that transportation-related emissions -- from projects such as road construction -- do not interfere with an area’s ability to reach its clean air goals.  Transportation conformity requirements become effective one year after the effective date of an area’s designation as nonattainment.
  • Once designated, nonattainment areas also are subject to new source review requirements. New Source Review is a permitting program for industrial facilities to ensure that new and modified sources of pollution do not impede progress toward cleaner air.
  • EPA and its partners at state, tribal and local agencies are taking action to cut particle pollution.  Efforts by states and tribes to attain the 1997 PM2.5 standards will help to reduce unhealthy levels of fine particle pollution.  In addition, EPA’s Clean Diesel Program is helping to reduce fine particle pollution across the country from highway, nonroad and stationary diesel engines.  Also, as a result of Federal programs to address interstate transport, levels of sulfur dioxide (which can form PM2.5) have also been reduced.  In some areas, wood smoke emissions are a significant contributor to fine particle pollution.  A wood stove or fireplace changeout campaign or other program targeting wood smoke emissions may reduce emissions and help the area attain the standards.


  • The Clean Air Act requires EPA to issue designations after the agency sets a new National Ambient Air Quality Standard (NAAQS) or revises an existing standard.  EPA formally designates areas as “nonattainment” (not meeting the standard), “unclassifiable/attainment” (meeting the standard or expected to be meeting the standard), or “unclassifiable” (insufficient data to classify).
  • On September 21, 2006, EPA revised its NAAQS for PM2.5 by significantly strengthening the 24-hour standards from 65 micrograms per cubic meter (µg/m3) to 35µg/m3.  Thousands of scientific studies have linked exposure to these tiny particles - approximately 1/30th the size of a human hair - with serious human health problems including premature death in people with heart and lung disease; nonfatal heart attacks; and increased hospital admissions and doctor and emergency room visits for respiratory and cardiovascular disease.
  • In June 2007, EPA provided guidance to states and tribes for recommending nonattainment area boundaries for the 24-hour PM2.5 standard.   EPA also used these factors and additional analytical tools, and other relevant information, to make final decisions on nonattainment area boundaries:
    • Emission data
    • Air quality data
    • Population density and degree of urbanization (including commercial development)
    • Traffic and commuting patterns
    • Growth rates and patterns
    • Meteorology (weather/transport patterns)
    • Geography/topography (mountain ranges or other air basin boundaries)
    • Jurisdictional boundaries (e.g., counties, air districts, Reservations, metropolitan planning organizations)
    • Level of control of emission sources
  • States and some tribes provided their initial designation recommendations in December 2007 based on the most recent three years of air quality monitoring data – generally 2004 to 2006.  In August 2008, EPA sent letters to state and tribal representatives responding to their initial recommendations for areas meeting and not meeting the 24-hour PM2.5 national ambient air quality standards.  States and tribes had 120 days to comment on EPA’s modifications to their recommendations, and to provide new information and analyses to EPA, if appropriate.
  • EPA also provided the public with a 30-day opportunity to comment on the Agency’s proposed modifications to the state and tribal recommendations and to offer additional information that could help establish the final nonattainment area boundaries. 
  • After reviewing the additional information received, in December 2008, EPA made decisions on area designations based on air quality monitoring data from 2005, 2006 and 2007.   Because air quality monitoring for 2008 was nearly complete, EPA agreed to evaluate the status of an area based on 24-hour PM2.5 air quality data from 2006-2008, if a state submitted complete, quality-assured, certified air quality data for 2008 before the designations became effective.
  • The December 2008 notice identifying areas as meeting and not meeting the standards was never published in the Federal Register and has been under review by the new EPA leadership.   Now that the 2008 air quality monitoring data for fine particle pollution have been quality assured and certified by the states, EPA was able to make final designations that reflect those air quality data. 


  • For more information on the designation process for the fine particle standards go to EPA’s Web site at www.epa.gov/pmdesignations.


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