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PM Standards

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September 21, 2006 - EPA strengthens National Ambient Air Quality Standards for Particle Pollution.



The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for six criteria pollutants, particle pollution (also known as particulate matter) is one of these. The Clean Air Act established two types of national air quality standards for particle pollution. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings.

The nation's air quality standards for particulate matter were first established in 1971 and were not significantly revised until 1987, when EPA changed the indicator of the standards to regulate inhalable particles smaller than, or equal to, 10 micrometers in diameter (that's about 1/4 the size of a single grain of table salt).

Ten years later, after a lengthy review, EPA revised the PM standards, setting separate standards for fine particles (PM2.5) based on their link to serious health problems ranging from increased symptoms, hospital admissions and emergency room visits for people with heart and lung disease, to premature death in people with heart or lung disease.

The 1997 standards also retained but slightly revised standards for PM10 which were intended to regulate "inhalable coarse particles" that ranged from 2.5 to 10 micrometers in diameter. PM10 measurements, however, contain both fine and coarse particles.

EPA revised the air quality standards for particle pollution in 2006. The 2006 standards tighten the 24-hour fine particle standard from the current level of 65 micrograms per cubic meter (µg/m3) to 35 µg/m3, and retain the current annual fine particle standard at 15 µg/m3. The Agency decided to retain the existing 24-hour PM10 standard of 150 µg/m3. The Agency revoked the annual PM10 standard, because available evidence does not suggest a link between long-term exposure to PM10 and health problems.

The Clean Air Act requires EPA to review the latest scientific information and standards every five years. Before new standards are established, policy decisions undergo rigorous review by the scientific community, industry, public interest groups, the general public and the Clean Air Scientific Advisory Committee (CASAC). More about the process of reviewing the standards.

National Ambient Air Quality Standards for Particle Pollution
Pollutant Primary Stds. Averaging Times Secondary Stds.
Particulate Matter (PM10) Revoked (1) Annual (1)
(Arithmatic Mean)		  
150 µg/m3 24-hour (2)  
Particulate Matter (PM2.5) 15.0 µg/m3 Annual (3)
(Arithmatic Mean)		 Same as Primary
35 µg/m3 24-hour (4)  

(see the complete table of National Ambient Air Quality Standards at http://www.epa.gov/air/criteria.html)
Units of measure for the standards are micrograms per cubic meter of air (µg/m3).
Footnotes:
(1) - Due to a lack of evidence linking health problems to long-term exposure to coarse particle pollution, the agency revoked the annual PM10 standard in 2006 (effective December 17, 2006).
(2) - Not to be exceeded more than once per year on average over 3 years.
(3) - To attain this standard, the 3-year average of the weighted annual mean PM2.5 concentrations from single or multiple community-oriented monitors must not exceed 15.0 µg/m3.
(4) - To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each population-oriented monitor within an area must not exceed 35 µg/m3 (effective December 17, 2006).

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