Region 1: EPA New England

What are the Air Quality Standards for PM?

National air-quality standards for PM were first established in 1971 and were not significantly revised until 1987 when EPA changed the indicator to focus on "inhalable particles", which are particles equal to or smaller than 10 microns (PM₁₀).

In July 1997, after evaluating hundreds of health studies and conducting an extensive peer-review process, EPA established PM standards that specifically addressed particles smaller than 2.5 microns (PM_2.5). The annual standard was set at 15 micrograms per cubic meter (μg/m³), based on the 3-year average of annual mean PM_2.5 concentrations. The 24-hour standard was set at 65 μg/m³ based on the 3-year average of the annual 98th percentile concentrations.  The 1997 standards retained, but slightly revised, standards for PM₁₀, which limited PM₁₀ concentrations to 50 μg/m³ based on an annual average, and 150 μg/m³ based on a 24-hour average.

Since 1997, EPA has evaluated thousands of new studies on PM and, in 2002, began to consider development of new PM standards.  On September 21, 2006, EPA revised the PM standards by lowering the level of the 24-hour PM_2.5 standard to 35 μg/m³ and retaining the level of the annual PM_2.5 standard at 15 μg/m³. The Agency also is retaining the 24-hour PM10 standard of 150μg/m3. However, the annual PM₁₀ standard is being revoked because of a lack of evidence establishing a link between long-term exposure to coarse particles and health problems.

Click here for more information on EPA's revisions to the National Ambient Air Quality Standards for particle pollution.