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In the summer of 1997, the Environmental Protection Agency (EPA) strengthened the air quality standards for two air pollutants, particulate matter and ozone, based on mounting scientific evidence of the harmfulness of these pollutants at levels allowed by the existing standards. With respect to particulate matter (PM), the agency found that numerous epidemiological studies had established an association between PM levels and premature deaths in humans, especially in the elderly population. Indeed, one study on which the EPA relied had found that approximately 60,000 premature deaths in the United States alone could be attributed, annually, to particulate matter. The scientific evidence on PM, however, did not all point in one direction, nor did it establish a causal theory as to why PM would cause death.

As for ozone, EPA responded to a substantial and growing body of scientific evidence linking ozone levels and the initiation and aggravation of respiratory problems, including asthma in children. This evidence, too, posed its share of challenges; in particular, the existing evidence seemed to point to the possibility that there is no level at which ozone exerts no effect whatsoever on the human body. That is, it is possible that ozone has some physiological effect, albeit perhaps a harmless one, on some person or group of persons at every level above zero.

The standards promulgated based on this body of scientific evidence were exceedingly complex. In setting new air quality standards for PM and ozone, EPA established not only an appropriate level for these pollutants in the ambient air, but also an averaging time, a statistical "form" (used to measure compliance with the standards), and, for particulate matter, an indicator (based on the size of particles to be regulated). The resulting "suite" of standards for PM and ozone, as EPA referred to them, thus consisted of a complex matrix of factors relating to air quality.


Reprinted with permission of the Saint Louis University Public Law Review © 2001 St. Louis University School of Law, St. Louis, Missouri.

Publication Citation

20 St. Louis U. Pub. L. Rev. 121-151 (2001)