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

Modifications to State and Tribal Recommendations for Areas Not Meeting the 24-Hour Fine Particle Standard Established in 2006



  • On August 19, 2008, the Environmental Protection Agency (EPA) sent letters to state and tribal representatives responding to their initial recommendations for areas meeting and not meeting the 24-hour national air quality standards for fine particles (PM2.5). States and tribes now have the opportunity to comment on EPA’s modifications to their recommendations, and to provide new information and analyses to EPA if appropriate.

  • On September 21, 2006, EPA revised its NAAQS for PM2.5 by significantly strengthening the 24-hour standard from 65 micrograms per cubic meter (μg/m3) to 35 μg/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.

  • After EPA sets a new National Ambient Air Quality Standard (NAAQS) or revises an existing NAAQS, EPA formally identifies or “designates” areas as attainment/unclassifiable (meeting the standard or expected to be meeting the standard despite a lack of monitoring data), nonattainment (not meeting the standard), or unclassifiable (insufficient data to classify).

  • EPA will provide the public with a 30-day opportunity to comment on the Agency’s proposed modifications to the state and tribal recommendations and offer additional information that may help establish the final nonattainment area boundaries. EPA will issue a Federal Register notice announcing the start of this comment period in the next few weeks.

  • States and 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. EPA plans to make final designations in December 2008 using air quality monitoring data from 2005, 2006 and 2007.

  • Once designations take effect, they become an important component of state, local and tribal governments’ efforts to reduce fine particle pollution. The designations govern what subsequent regulatory actions states, tribes, and EPA must take in order to improve or preserve air quality in each area.

  • 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.


  • After EPA makes final attainment and nonattainment designations in December, areas designated nonattainment across the country will be required to take action to improve their air quality.

  • Areas that will be designated attainment/unclassifiable will not have to take steps to improve air quality but they must take steps to help prevent their air quality from deteriorating to unhealthy levels.

  • The Clean Air Act requires state, local and tribal governments to take steps to control particle pollution in nonattainment areas. Those steps may include stricter controls on industrial facilities and additional planning requirements for transportation-related sources.

  • State, local and tribal governments must detail control requirements in plans demonstrating how they will meet the 2006 PM2.5 NAAQS. Those plans are known as state or tribal implementation plans, or SIPs/TIPs. States and tribes must submit their plans to EPA within three years after the Agency makes final designations — by April 2012. Areas are required to attain clean air by 2014. EPA may grant attainment date extensions of 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 local transportation and air quality officials to 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 an area is designated 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.

  • In June 2007, EPA provided guidance to states and tribes for recommending nonattainment area boundaries for the 24-hour PM2.5 standard.

    • Rather than establish a presumption for the minimum size of an area, EPA instructed states and tribes to evaluate each area on a case-by-case basis.

    • As a starting point, EPA expected that 24-hour PM2.5 nonattainment areas would include counties with monitors violating the 24-hour fine particle standard and nearby counties that contribute to that violation.

    • EPA also recommended that states and tribes consider using common boundaries for areas to be designated as nonattainment for both the annual and 24-hour PM2.5 standards. Common boundaries will make planning and implementation easier for states and tribes.

  • In addition, EPA recommended that states and tribes consider the following nine factors in assessing whether to include a county in a nonattainment area, as well as any other relevant information:
  1. Emission data
  2. Air quality data
  3. Population density and degree of urbanization (including commercial development)
  4. Traffic and commuting patterns
  5. Growth rates and patterns
  6. Meteorology (weather/transport patterns)
  7. Geography/topography (mountain ranges or other air basin boundaries)
  8. Jurisdictional boundaries (e.g., counties, air districts, Reservations, metropolitan planning organizations)
  9. Level of control of emission sources

    EPA is also using these factors and additional analytical tools to make final decisions on designations and nonattainment area boundaries.


  • For more information on the designation process for the fine particle standards, and to view individual letters from EPA to states and tribes, go to EPA’s Web site at www.epa.gov/pmdesignations.

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