22 December 2005

The US Environmental Protection Agency (EPA) has proposed revisions to its national ambient air quality standards (NAAQS) for particulate matter. The main provisions of the proposal are:

  • PM2.5 24-Hour Standard—The standard limiting daily concentration of fine particles below 2.5 µm would be tightened to 35 µg/m3, from the current 65 µg/m3.
  • PM2.5 Annual Standard—The current PM2.5 standard of 15 µg/m3 remains unchanged.
  • PM10-2.5 24-hour standard—A daily standard of 70 µg/m3 is proposed for particles between 2.5 and 10 µm. The new PM10-2.5 category would include coarse particles that come from sources typically found in urban areas, such as high density traffic on paved roads, industrial sources and construction activities. The standard would not cover coarse particles from such sources as windblown dust and soils, agricultural or mining sources.
  • PM10 24-hour standard—The current daily PM10 standard of 150 µg/m3 would be revoked, except in urban areas with a population of 100,000 or more.

The proposed standards are weaker than the recommendation of the EPA’s Clean Air Scientific Advisory Committee. The EPA staff paper of June 2005 called for a stronger fine particulate limit of 14 to 13 µg/m3, and for a daily limit of 35 to 30 µg/m3.

Health and environmental groups, including the American Lung Association, had called for an even stronger annual standard of 12 µg/m3, equal to standards adopted by California and to limits recommended by some Northeast states.

Some electric utilities, on the other hand, considered the EPA proposal too stringent. They noted that in 2003 PM2.5 concentration dropped to its lowest level since 1999, when EPA began nationwide monitoring of PM2.5 pollution.

The current PM2.5 standards were adopted in 1997, but due to legal challenges the enforcement started only in 2004. Ambient PM10 standards were first adopted in 1987.

The EPA is required by a consent decree to issue a final rule for the particle pollution standards by 27 September 2006.

Source: US EPA (regulatory documents | EPA staff paper, June 2005)