Microsoft Word - nejm v3 final - pdf version.doc

Abstract Background: Time-series analyses have linked contemporary levels of air pollution, particularly particles, to daily mortality counts. These findings have contributed to the rationale for tightening air quality standards, but the validity of these findings has been questioned. We have developed analytic methods to address limitations of prior single-city time-series analyses by combining evidence across multiple locations. Methods: Using a two-stage analytic approach that pools evidence from multiple locations, we have assessed the effects of five major outdoor air pollutants, particulate matter less than 10 µm in aerodynamic diameter (PM 10 ), ozone (O 3 ), carbon monoxide (CO), sulfur dioxide (SO 2 ), and nitrogen dioxide (NO 2 ), on daily mortality in 20 of the largest cities in the United States, from 1987-1994. Results: We found consistent evidence that PM 10 is associated with total and cardiorespiratory mortality after taking into account potential confounding by other pollutants. For total mortality, the estimated relative rate was approximately a 0.5% increase in mortality per 10 µg/m 3 increase in PM 10 and the effect was not likely to be due to chance. There was weaker evidence that ozone increased mortality during the summer but not the winter months. Other pollutants did not have effects on mortality. Conclusions: The analyses provide evidence that air pollution with particles is still adversely affecting the public's health and strengthen the rationale for limiting concentrations of respirable particles in outdoor air. Air Pollution and Mortality in 20 U.S. Cities