Acid rain regulations adopted in the 1980s have already caused a significant reduction in particulate pollution, says Douglas Dockery of Harvard University. The reason? Coal-burning power plants were compelled to clean up their emission of sulfur dioxide, and in the process also reduced particle emissions.

Similarly, the new regulations could have ancillary benefits by redistributing the pollution-control burden. Much of the air pollution along the Eastern Seaboard originates in coal-burning power plants in Midwestern states that are now in compliance with the Clean Air Act. Tightening the Act would force these upwind areas to reduce their pollution and thus help polluted cities downwind reduce their control costs.

Sick cities
One of the best sources of information on particulates is a long-term epidemiological study of residents of six small cities in the United States. Begun in the early 1970s at the Harvard School of Public Health, the study monitors air quality and health of 8,000 adults and 14,000 children who live near coal-burning power plants.

When air in each city was analyzed for its constituent pollutants, particles smaller than 2.5 micrometers (the so-called PM-2.5) turned out be the most toxic components in the air. In fact, residents of Steubenville, Ohio, where the PM-2.5 concentration was 29.6 micrograms (defined) per cubic meter, were 1.26 times as likely to die during the study as people in Portage, Wis., where PM-2.5 was 11 micrograms per cubic meter. (Pristine Portage happens to be just north of The Why Files headquarters.) The calculation was made after correcting for other risk factors like age, sex, education level, occupational exposure and cigarette smoking.

The PM-2.5 concentration in Steubenville would trigger corrective measures under the new EPA proposal, which would limit PM-2.5 to 50 micrograms per cubic meter on daily measurements, and 15 micrograms per cubic meter for the annual average. Yet the American Lung Association, noting that there seems to be no safe level of PM-2.5, is urging a cleaner standard to a daily limit of 18 micrograms per cubic meter and an annual limit of 10. See "An Association Between Air Pollution..." in the bibliography.

Yet particulates were not nearly as effective in causing death as cigarettes -- current smokers were 2.00 times as likely to die during the study as non-smokers. And former smokers were 1.39 times as likely to die.

Particulates may also be less unhealthy than good, old "it-ain't-the-heat-it's-the-humidity" summer weather. University of Delaware geographer Lawrence Kalkstein has correlated large increases in mortality rates with hot, humid weather (see "Air Mass Murderer" in the bibliography).