The use of improved exposure factors in the interpretation of fine particulate matter epidemiological results

Multi-city population-based epidemiological studies have consistently reported a significant association between ambient fine particulate matter (PM_2.5) concentrations and daily mortality. However, in these studies heterogeneity between-community effect estimates is often observed but not thoroughly examined, leaving much of the difference in the effects of individual communities inadequately explained. In this study, we evaluated whether community-specific exposure factors play a role in explaining heterogeneity in the associations between ambient PM_2.5 concentrations and several causes of mortality in 27 US communities from 1997 to 2002 as reported by Franklin et al. (J Expo Sci Environ Epidemiol 3:279–287, 2007). Using publically available databases, we created factors capturing home ventilation characteristics and commuting patterns. These factors include the normalized leakage, annual and seasonal temperatures, and in-vehicle commuting distances and time. In-vehicle commuting distance and time, and annual, spring, and fall temperatures were significant negative effect modifiers of the relationship between PM_2.5 exposure and respiratory and non-accidental mortality. Additionally, cardiovascular mortality PM_2.5 effect estimates were negatively modified by in-vehicle commuting distances. We concluded that future multi-community studies of particle health effects should consider these and other determinants of personal–ambient exposure relationships during the epidemiological analysis.