ISEE-79 Abstract: While a convincing body of evidence has accumulated regarding the association of coronary and respiratory disease with acute exposures to particulate air pollution, few studies have examined the effects of chronic exposures. We are evaluating the association of long term exposure to air pollution with incident coronary and respiratory disease and with total mortality in the Nurses’ Health Study, an ongoing prospective cohort study of 121,700 women residing throughout the U.S. Between 1986 and 2000, 6,617 incident cases of cardiovascular disease, and 1,292 incident lung cancer cases have been reported. Confirmed prevalent cases of adult-onset respiratory disease include 2,092 cases of COPD and 5,823 cases of asthma. At enrollment in 1976, the participants resided in 11 large industrial states – California, Connecticut, Florida, Maryland, Massachusetts, Michigan, New York, New Jersey, Ohio, Pennsylvania, and Texas. By 2000, there were at least 10 residents in all 50 states and DC. Addresses from 1986 through 2002 are available, and will be used to track residence throughout the study period. This residential history will be linked to yearly ambient air pollution levels using geographic information system (GIS) software. We will model air shed-specific, long-term exposure to air pollution for each participant for the relevant years using data from the Environmental Protection Agency’s Air Quality System (AQS), the national Emissions Trends database, the National Oceanic and Atmospheric Association, U.S. census data, and commercially available traffic data. In addition, area-specific information about home characteristics and ventilation patterns will be incorporated into the analysis, as will existing ambient monitoring data from specific sites, where available. Within each airshed, we will estimate annual average PM2.5 and sulfate concentrations at the latitude and longitude of each monitor using regression models based on measured particulate concentrations, site-specific traffic and population density, distance to roadway, land use, emission estimates, and visible range data from the nearest airport. To account for long-range transport, models will also include mean pollutant concentrations from neighboring air sheds. Kriging and other geographical smoothing techniques will be incorporated to account for any remaining spatial correlation. Since the coverage of the pollution databases is incomplete, it is likely that the study population will be restricted to areas in which sufficient pollution data are available. At a minimum, this will include participants living in the original eleven states, where the majority of the population still resides.