Dark Clouds on the Hazy Horizon
March 2006

In the Phoenix metropolitan area, November and December 2005 were filled with high pollution advisories, no burn restrictions, and pleas to carpool and reduce driving. These alerts were also a signal to regulators and the regulated community alike that additional efforts will be required to address particulate matter pollution in the Phoenix area.


A. Standards and Nonattainment History
As part of the comprehensive approach to address air pollution, Section 109 of the Clean Air Act, 42 U.S.C. §7409, requires EPA to establish National Ambient Air Quality Standards (NAAQS) for a number of pollutants. In 1987, EPA established two standards for particulate matter that is 10 microns or less (PM10); a 24-hour standard of 150 micrograms/m3 and an annual standard of 50 micrograms/m3.

On November 15, 1990, the Phoenix metropolitan area, which had already been designated as an area that did not meet an earlier particulate matter NAAQS, was designated a “moderate” PM

10 nonattainment area. Under that designation, the Phoenix area had to meet the PM10 NAAQS by December 1994.

That deadline came and went. As a result, effective June 10, 1996, EPA reclassified the Phoenix metropolitan area as a “serious” nonattainment area. This designation triggered additional requirements but ultimately provided more time to show attainment.

B. Demonstrating Attainment

The current PM10 attainment deadline is December 31, 2006. However, because of the methodology used to determine whether an area is in attainment, the December 2006 deadline is misleading. To demonstrate attainment for the 24-hour standard, the expected number of exceedances per year at a site must be less than or equal to one per year, averaged over a three year period. Numerous exceedances in 2005 would preclude the area from demonstrating attainment until 2008, even if 2006 and 2007 had no exceedances. As a result, the Phoenix area has run out of time to show attainment.

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