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History of PM Standards
- 1971- EPA issued the first National Ambient Air Quality Standards for Total Suspended Particles (TSP).
- 1987- EPA revised the standards. The Agency replaced TSP with PM10 to target inhalable particles equal to or smaller than 10 micrometers, about one quarter the size of a single grain of table salt. The 24-hour PM10 standard was set at150 micrograms per cubic meter (µg/m3), and the annual PM10 standard was set at 50 µg/m3.
- 1997- EPA revised the PM standards. The Agency added standards for PM2.5 to target particles equal to or smaller than 2.5 micrometers. These fine particles are associated with serious health effects. The PM2.5 standards were set at 15 µg/m3 (annual mean) and 65 µg/m3 (24-hour average). In addition, the Agency revised the way exceedances were calculated for the 24-hour PM10 standard.
- 1997- Several industries, other organizations, and some state governments challenged EPA’s standards in the U.S. Court of Appeals for the D.C. Circuit.
- 2001- The U.S. Supreme Court upheld EPA’s authority under the Clean Air Act to set standards and clarified that EPA cannot consider cost in setting standards. The Court remanded several issues to the appellate court.
- 2002- The DC Circuit Court rejected all remaining legal challenges to EPA’s 1997 standards for PM2.5.
- 2004- EPA designated 39 areas as not meeting the standards for annual PM2.5.
- 2006 - EPA revised the PM standards. The Agency tightened the 24-hour PM2.5 standard from 65 micrograms µg/m3 to 35 µg/m3 and retained the annual PM2.5 standard at 15 µg/m3. The 24-hour PM10 standard of 150 µg/m3 was retained. The Agency revoked the annual PM10 standard because available evidence does not suggest a link between long-term exposure to PM10 and health problems.
- 2009 - EPA designated areas as attainment and nonattainment for the 24-hour PM2.5 standard set in 2006.
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