Spatial variation in particulate concentrations within metropolitan Philadelphia

During the summers of 1992 and 1993, particle mass concentrations (PM(2.5) and PM(10)) were measured at eight sites located within metropolitan Philadelphia. Particle sampling was performed simultaneously at these sites on alternate days during the summer of 1992 and every day at seven of these sites during the summer of 1993. Sampling was conducted over 24-h periods beginning at 9 AM (EDT) during both summers. All PM(2.5) and PM(10) samples were collected using 10 L/min inertial impactors with particle cutpoints of 2.5 and 10 mu m, respectively. In this paper, we examine the relationship among PM(2.5), coarse particulate (2.5 < d(a) < 10 mu m), and PM(10) concentrations. In addition, we analyze their spatial variation and compare our findings with those made in an earlier study of sulfate (SO42-) concentrations. PM(2.5) and PM(10) concentrations were found to be relatively uniform across Philadelphia, suggesting that concentrations measured at a single monitoring site are able to characterize particulate concentrations across Philadelphia and other similar urban areas well. Coarse particulate concentrations were found to vary spatially within Philadelphia, with its variation related to population density. Coarse particulate levels were also shown to vary by day of week as weekday levels were higher than weekend levels. Variability in PM(10) concentrations was driven primarily by variability in PM(2.5) concentrations, which in Philadelphia comprised approximately 75% of PM(10). SO42- related species in Philadelphia were, in turn, responsible for variability in PM(2.5) and, as a result, in PM(10) as well. SO42--associated species were the largest component of both PM(2.5) and PM(10) concentrations, comprising approximately 65 and 50% of their concentrations, respectively.