Personal exposures to PM2.5 mass and trace elements in Baltimore, MD, USA

In a recent study, EPA found a significant relationship between PM2.5 mass measurements at a community site and personal exposure samples in a Towson, MD retirement facility. This manuscript builds upon the mass concentration results by evaluating the exposure relationships with the elemental composition of the PM2.5 mass. Daily community, outdoor, and indoor PM2.5 were measured with a URG Versatile Air Pollutant Sampler (VAPS). Daily personal and apartment PM2.5 samples were collected with a Marple Personal Exposure Monitor (PEM). Only subjects with the most complete data records (n=10) were used in this analysis. Significant differences were found between the VAPS and PEM samplers for PM2.5 elemental composition, so all subsequent analyses were conducted independently for each of the data sets. Both the VAPS and PEM samples were analyzed with energy dispersive X-ray fluorescence (XRF). In addition, the VAPS samples were analyzed for pH, major ions, and elemental/organic carbon. The spatial correlation coefficients between the community and outdoor monitor, and the indoor infiltration rates were calculated for several PM2.5 constituents calculated from the VAPS samples including sulfate, nitrate, trace element oxides, soil, and NaCl. The spatial correlations for most PM2.5 constituents were good (e.g. sulfate (r2=0.99)), with the exception of soil (r2=0.40). Infiltration rates of the PM2.5 constituents were determined by linear regression analysis and varied according to particle size. Infiltration rates ranged from 0.41 (r2=0.98) for sulfate to 0.09 (r2=0.83) for nitrate. Outdoor, central indoor, apartment, and personal exposures PEM samples were also evaluated using a linear mixed effects model and median Pearson correlation coefficients. The modeling results indicate that personal exposures to PM2.5 and sulfate were strongly associated with outdoor concentrations. Conversely, personal exposures to soil and trace element oxides were not significantly correlated to outdoor concentrations.