BALTIMORE--The fine particulate air pollution found in and around US cities is associated with an increased risk of death from all causes and from cardiovascular and respiratory illness, a new study shows.[1] The results expand on data in older air pollution studies, showing a compelling link between small airborne particles and mortality. Those studies were criticized for often limiting their examination to one city.

The new study addresses the earlier criticisms and covers 20 metropolitan areas, making it one of the most definitive studies of its kind. Thus, its findings reinforce the public-health rationale for national regulations to control fine particulate air pollution, lead author Jonathan M. Samet, MD, told RESPIRATORY REVIEWS. Dr. Samet is a Professor and Chair of the Department of Epidemiology at the Johns Hopkins University School of Public Health, in Baltimore.

From 1987 through 1994, the authors assessed the effect of five prominent outdoor air pollutants--ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and particulate matter less than 10 µm in aerodynamic diameter (PM10)--on daily mortality in the 30 US counties with the largest populations. These counties had a total population exceeding 50 million and included many major cities.

The counties' air pollution data came from the Aerometric Information Retrieval System, an Environmental Protection Agency (EPA) database. Daily mortality rates were available from the National Center for Health Statistics. After excluding nonresident and homicide-, accident-, and suicide-related deaths, the authors classified mortality by age and cause.

The average number of deaths per day was substantial during the study period, ranging from 17.5 in Atlanta to 190.9 in New York. The mean daily PM10 ranged from 23.8 to 46 µg/m3, considerably lower than the 150 µg/m3 maximum allowed in a 24-hour period by EPA standards.

The results of this investigation support those of earlier studies, said James H. Ware, PhD, in an accompanying editorial.[2] "The evidence in support of an association between the concentration of particulate air pollution and the mortality rate is consistent, is not affected by differences in statistical methods, and can be generalized," wrote Dr. Ware, a Professor at the Harvard School of Public Health, in Boston.

He recommends aggressive research on PM2.5 (particulate matter less than 2.5 µm in aerodynamic diameter), which better represents the size of particles that can penetrate the airways and alveoli. The EPA added standards for control of PM2.5 in 1997. In 1999, the agency was blocked from implementing those standards by the Court of Appeals for the District of Columbia. The US Supreme Court will hear an appeal of that decision during its current session.

--Timothy Begany

References
1. Samet JM, Dominici F, Curriero FC, et al. Fine particulate air pollution and mortality in 20 U.S. cities, 1987-1994. N Engl J Med. 2000;343:1742-1749.

2. Ware JH. Particulate air pollution and mortality—clearing the air [editorial]. N Engl J Med. 2000; 343:1798-1799.