Composition of PM(2.5) and PM(10) aerosols in the IMPROVE network

PM(2.5) and PM(10) particulate concentrations measured at 42 sites in the Interagency Monitoring of Protected Visual Environments (IMPROVE) network at Class I visibility areas throughout the United States over the 1993 seasonal year showed well-defined regional patterns. The PM,, concentration had a large gradient from West to East, averaging 3 mu g/m(3) in most of the West compared to 13 mu g/m(3) in the Appalachian region. Coarse particle concentration (2.5-10 mu m) exhibited a small gradient from North to South, but no gradient from West to East. No change in PM(2.5) or PM,, was observed from 1988 to 1993 for sites with complete records. The elemental concentration (H, Na-Pb) was determined from all PM(2.5) Teflon filters and from the PM(10) filters from four sites: an eastern and western urban site (Washington, D.C. and South Lake Tahoe) and the nearest Class I site (Shenandoah and Bliss). Soil was the largest component of the coarse particle concentration. Sulfur accounted for 3% of the coarse particle concentration in the western pair, and 16-24% in the eastern pair. The urban sites had more organic, elemental carbon, and nitrate in the PM(2.5) fraction than the associated Class I sites, and more soil and organics in the coarse particle fraction.