Determinants of the associations between ambient concentrations and personal exposures to ambient PM2.5, NO2, and O3 during DEARS

Abstract

Personal total exposure (Et) is composed of exposure to pollutants of ambient origin (Ea) and nonambient origin (Ena), both of which are associated with health effects. However, Ea is more relevant for estimating the health effects associated with ambient air pollutants. Associations between Ea and ambient concentrations (Ca) were examined for different subpopulations in the Detroit Exposure and Aerosol Research Study (DEARS). First, Ea was estimated for PM2.5, NO2, and O3. The associations between Ca and Ea were then characterized with mixed effect models. Ca served as a good surrogate for Ea for PM2.5 in both summer (slope = 0.80) and winter (slope = 0.55), but only in summer for O3 and NO2 (slope = 0.13 for NO2, and slope = 0.03 for O3).The effects of exposure determinants on Ea–Ca associations were examined using mixed effect models. Exposure determinants examined include personal activities, building and household characteristics and ambient apparent temperature (AT). The strength of associations between Ca and Ea differed between that for the entire study population and different subpopulations, which in turn differed from each other. Personal activities and building characteristics significantly affected the Ea–Ca associations through modifying the air exchange rate (AER). Ca was not a significant indicator of Ea for O3 and NO2 for homes with central AC or with windows closed. Ambient AT affected the Ea–Ca associations through modifying both AER and personal activities. The fraction of daily time spent outdoors peaked (6%) at about 22 °C, and monotonically decreased when ambient AT departed from 22 °C. Adequate accounting for the effects of exposure determinants on the Ea–Ca associations will lead to a better understanding of the Ea–Ca associations and of the uncertainties associated with using ambient concentrations as surrogates for personal exposures of ambient origin.