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Joel Schwartz,^1,2,3 Francine Laden,^1,3 and Antonella Zanobetti¹

¹Environmental Epidemiology Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA; ²Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA; ³Channing Laboratory, Brigham and Women's Hospital, and Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA

Abstract

Particulate air pollution at commonly occurring concentrations is associated with daily deaths. Recent attention has focused on the shape of the concentration-response curve, particularly at low doses. Several recent articles have reported that particulate matter with aerodynamic diameter 10 µm (PM₁₀) was associated with daily deaths with no evidence of a threshold. These reports have used smoothing or spline methods in individual cities and pooled the results across multiple cities to obtain estimates that are more robust. To date, fine particulate matter (aerodynamic diameter 2.5 µm ; PM_2.5) , a component of PM₁₀, has not been examined in this regard. We examined this association in a hierarchical model in six U.S. cities. In the first stage, we fit log-linear models including smooth functions of PM_2.5 in each city, controlling for season, weather, and day of the week. These smooth functions allowed for nonlinearities in the city-specific associations. We combined the estimated curves across cities using a hierarchical model that allows for heterogeneity. We found an essentially linear relationship down to 2 µg/m³. The same approach was applied to examine the concentration response to traffic particles, controlling for particles from other sources. Once again, the association showed no sign of a threshold. The magnitude of the association suggests that controlling fine particle pollution would result in thousands fewer early deaths per year. Key words: meta-analysis, mortality, particulate air pollution, smoothing, time series, traffic. Environ Health Perspect 110:1025-1029 (2002) . [Online 27 August 2002]

http://ehpnet1.niehs.nih.gov/docs/2002/110p1025-1029schwartz/ abstract.html

Address correspondence to J. Schwartz, Environmental Epidemiology Program, Harvard School of Public Health, 665 Huntington Ave., Boston, MA 02115 USA. Telephone: (617) 384-8752. Fax: (617) 384-8745. E-mail: jschwrtz@hsph.Harvard.edu

This work was supported by U.S. EPA Grant R827353 and NIEHS Grant ES 00002.

Received 21 December 2001 ; accepted 20 March 2002.