AN ASSOCIATION BETWEEN AIR-POLLUTION AND MORTALITY IN 6 UNITED-STATESCITIES

Background. Recent studies have reported associations between particul ate air pollution and daily mortality rates. Population-based, cross-s ectional studies of metropolitan areas in the United States have also found associations between particulate air pollution and annual mortal ity rates, but these studies have been criticized, in part because the y did not directly control for cigarette smoking and other health risk s. Methods. In this prospective cohort study, we estimated the effects of air pollution on mortality, while controlling for individual risk factors. Survival analysis, including Cox proportional-hazards regress ion modeling, was conducted with data from a 14-to-16-year mortality f ollow-up of 8111 adults in six U.S. cities. Results. Mortality rates w ere most strongly associated with cigarette smoking. After adjusting f or smoking and other risk factors, we observed statistically significa nt and robust associations between air pollution and mortality. The ad justed mortality-rate ratio for the most polluted of the cities as com pared with the least polluted was 1.26 (95 percent confidence interval , 1.08 to 1.47). Air pollution was positively associated with death fr om lung cancer and cardiopulmonary disease but not with death from oth er causes considered together. Mortality was most strongly associated with air pollution with fine particulates, including sulfates. Conclus ions. Although the effects of other, unmeasured risk factors cannot be excluded with certainty, these results suggest that fine-particulate air pollution, or a more complex pollution mixture associated with fin e particulate matter, contributes to excess mortality in certain U.S. cities.