Prospective cohort studies constitute the major source of evidence about the mortality effects of chronic exposure to particulate air pollution. Additional studies are needed to provide evidence on the health effects of chronic exposure to particulate matter ? 2.5 ?m in aerodynamic diameter (PM2.5) because few studies have been carried out and the cohorts have not been representative. This study was designed to estimate the relative risk of death associated with long term exposure to PM2.5 by region and age groups in a U.S. population of elderly, for the period 2000

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