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 metropoli tan Philadelphia. Particle sampling was performed simultaneously at th ese sites on alternate days during the summer of 1992 and every day at seven of these sites during the summer of 1993. Sampling was conducte d over 24-h periods beginning at 9 AM (EDT) during both summers. All P M(2.5) and PM(10) samples were collected using 10 L/min inertial impac tors 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 ana lyze 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 Philadel phia, suggesting that concentrations measured at a single monitoring s ite are able to characterize particulate concentrations across Philade lphia and other similar urban areas well. Coarse particulate concentra tions were found to vary spatially within Philadelphia, with its varia tion related to population density. Coarse particulate levels were als o shown to vary by day of week as weekday levels were higher than week end levels. Variability in PM(10) concentrations was driven primarily by variability in PM(2.5) concentrations, which in Philadelphia compri sed approximately 75% of PM(10). SO42- related species in Philadelphia were, in turn, responsible for variability in PM(2.5) and, as a resul t, in PM(10) as well. SO42--associated species were the largest compon ent of both PM(2.5) and PM(10) concentrations, comprising approximatel y 65 and 50% of their concentrations, respectively.