Study Says New Particulate Matter Rules Unnecessary

Published November 21, 2003

Air quality in the United States is good and will continue to improve in coming years, according to a newly published report written by Competitive Enterprise Institute adjunct scholar Joel Schwartz.

The findings of the report, Particulate Air Pollution: Weighing the Risks, challenge the assumption of many activists and politicians that current low levels of particulate matter pose a significant health risk and require increased federal regulation.

“Evidence from multiple medical studies suggests that exposure to particulate matter at current levels has little or no effect on mortality in the United States. Regardless, processes already set in motion guarantee substantial reductions in coming years,” wrote Schwartz.

Air quality in the U.S. has improved dramatically in recent decades due to emission reductions from industrial facilities and motor vehicles. The country achieved that success despite substantial increases in population, automobile travel, and energy production. Air pollution will continue to decline, reports Schwartz, because more recent vehicle models start out cleaner than earlier models and stay cleaner as they age, and also because already-adopted standards for new vehicles and existing power plants and industrial facilities will take effect in the next few years.

Nonetheless, both the Bush administration and congressional Democrats have proposed sweeping new measures aimed at power-plant particulate matter (PM) emissions. The proposals are largely justified by claims that current PM levels pose a serious public health threat.

Tighter Regulation Not Justified

Those claims rest on a weak foundation, asserts Schwartz. The U.S. Environmental Protection Agency (EPA) based its new annual fine PM (PM2.5) standard on a study known as the American Cancer Society (ACS) study of PM and mortality, which assessed the association between the risk of death between 1982 and 1998 with PM2.5 levels in dozens of American cities.

Although the ACS study reported an association between PM and mortality, some odd features of the ACS results suggest PM is not the culprit. For example, according to the ACS study, PM increased mortality in men, but not women; in those with no more than a high school diploma, but not those with at least some college education; in former smokers, but not in current smokers or persons who never smoked; and in those who said they were moderately active, but not in those who said they were very active or sedentary.

The ACS study offered no explanation for these odd, biologically implausible variations in the relationship between PM2.5 and mortality. Moreover, the ACS study reported that higher PM2.5 levels were not associated with an increased risk of mortality due to respiratory disease; a surprising finding, given that particulate matter air pollution would be expected to exert its effects through the respiratory system.

According to Schwartz, EPA also ignored the results of another epidemiologic study that found no effect of PM2.5 on mortality in a cohort of veterans with high blood pressure, even though this relatively unhealthy cohort should have been more susceptible to the effects of pollution than the general population.

The evidence, according to Schwartz, suggests the PM2.5 standard is unnecessarily stringent. Attaining it will be expensive and unlikely to improve public health.

“Additional near-term reductions in PM are probably best achieved by dealing with the stock of high-polluting older vehicles that account for a substantial portion of ambient PM levels in metropolitan areas,” concludes Schwartz. “This flexible, more cost-effective approach is far more likely to result in net public health benefits than other proposals that are the focus of current legislative and regulatory activity and debate.”

James M. Taylor is managing editor of Environment & Climate News. His email address is [email protected].