Geographic differences in inter-individual variability of human exposure to fine particulate matter

► Most human exposure to ambient fine particulate matter (PM2.5) occurs indoors. ► Ambient exposure to concentration (Ea/C) for PM2.5 averages 0.52-0.60. ► Average Ea/C varies with geographic differences in residential air exchange rates. ► The coefficient of variation of inter-individual variability in Ea/C is 0.25. ► Variations in Ea/C are not accounted for in many health effects studies.