Development and Evaluation of Alternative Metrics of Ambient Air Pollution Exposure for Use in Epidemiologic Studies

Abstract

Population-based epidemiologic studies of air pollution have traditionally relied upon imperfect surrogates of personal exposures, such as area-wide ambient air pollution levels based on readily available outdoor concentrations from central monitoring sites. This practice may introduce exposure misclassification in epidemiologic analyses for pollutants that are spatially heterogeneous, including those associated with traffic emissions (i.e., carbon monoxide, elemental carbon, nitrogen oxides, and particulate matter). To investigate the potential impact of misclassification within observed health risk estimates, U.S. EPA in collaboration with Emory University is develo** and evaluating several tiers of exposure metrics for ambient traffic-related and regional pollutants that vary in their approaches for modeling pollutant spatial heterogeneity. The following tiers of exposure metrics are examined: (1) central site monitoring data, (2) local scale modeling (AERMOD), and (3) combined regional and local scale modeling. Each metric is applied in two extensive, ongoing epidemiologic studies conducted by Emory University to examine ambient air pollution and acute morbidity in Atlanta, GA. We hypothesize that using the more refined exposure estimates will provide greater power to detect epidemiologic associations of interest, particularly for heterogeneous, traffic-related pollutants. This research will be useful for improving exposure assessment in future air pollution epidemiology studies, by providing alternative methods as well as by providing a further understanding of to the situations that might require refined exposure metrics.