Longitudinal variability in outdoor, indoor, and personal PM2.5 exposure in healthy non-smoking adults

Multiple 24-h average outdoor, indoor and personal PM2.5 measurements were made in a population of healthy non-smoking adults from the Minneapolis-St. Paul metropolitan area between April and November 1999. Personal (P) PM2.5 concentrations were higher than indoor (I) concentrations, which were higher than outdoor (O) concentrations. For 28 adults with a median of 9 (range 5–11) measurements per person, the distribution of longitudinal (i.e., within-person) correlation coefficients between P and I was moderate (median r=0.45). The distribution of longitudinal correlation coefficients between I and O concentrations showed that these variables were less strongly associated (median r=0.25; 28 residences; measurement median n=10 per residence, range 7–13), and the distribution of P and O correlation coefficients (median r=0.02; 29 subjects; measurement median n=11 per subject, range 7–15) showed little statistical relation between these two variables for a majority of participants. A sensitivity analysis indicated that correlations did not increase if days with exposure to environmental tobacco smoke or occupational exposures were excluded. On average these adults spent 91% of their time indoors, and the mean of the average PM2.5 “personal cloud” was 15.3 μg/m3. Participants who had the largest personal cloud values tended to work outside the home and spent more time outdoors than subjects who did not work outside the home. In this population of healthy non-smoking adults, personal exposure to PM2.5 does not correlate strongly with outdoor central site PM2.5 concentrations.