Assessing the relationship between personal particulate and gaseous exposures of senior citizens living in Baltimore, MD

We conducted a multi-pollutant exposure study in Baltimore, MDI in which 15 non-smoking older adult subjects (>64 years old) wore a multi-pollutant sa mpler for 12 days during the summer of 1998 and the winter of 1999. The sam pler measured simultaneous 24-hr integrated personal exposures to PM2.5, PM 10, SO42-, O-3, NO2, SO2, and exhaust-related VOCs. Results of this study showed that longitudinal associations between ambient PM2.5 concentrations and cofresponding personal exposures tended to be hig h in the summer (median Spearman's r = 0.74) and low in the winter (median Spearman's r = 0.25). Indoor ventilation was an important determinant of pe rsonal PM2.5 exposures and resulting personal-ambient associations. Associa tions between personal PM2.5 exposures and corresponding ambient concentrat ions were strongest for well-ventilated indoor environments and decreased w ith ventilation. This decrease was attributed to the increasing influence o f indoor PM2.5 sources. Evidence for this was provided by SO42- measurement s, which ran be thought of as a tracer for ambient PM2.5. For SO42-, person al-ambient associations were strong even in poorly ventilated indoor enviro nments, suggesting that personal exposures to PM2.5 of ambient origin are s trongly associated with corresponding ambient concentrations. The results a lso indicated that the contribution of indoor PM2.5 sources to personal PM2 .5 exposures was lowest when individuals spent the majority of their time i n well-ventilated indoor environments. Results also indicate that the potential for confounding by PM2.5 co-pollut ants is limited, despite significant correlations among ambient pollutant c oncentrations. In contrast to ambient concentrations, PM2.5 exposures were not significantly correlated with personal exposures to PM2.5-10, PM2.5 of non-ambient origin, O-3, NO2, and SO2. Since a confounder must be associate d with the exposure of interest, these results provide evidence that the ef fects observed in the PM2.5 epidemiologic studies are unlikely to be due to confounding by the PM2.5 co-pollutants measured in this study.