MULTIMODAL SIZE SPECTRA OF SUBMICROMETER PARTICLES BEARING VARIOUS ELEMENTS IN RURAL AIR

Samples of size-segregated submicrometer aerosol particles were collected with a microorifice impactor near Deep Creek Lake, a recreational area in rural western Maryland, and analyzed for up to 44 elements by instrumental neutron activation and X-ray fluorescence analyses. Differential concentration vs particle size spectra revealed as many as four distinct submicrometer aerosol modes with diameters between 0.09 and 1.0-mu-m in a single sample. The spectra of many elements, including Al, Zn, Na, K, Br, Ca, Ga, Fe, La, Sb, Ce, Ti, and I contained two or more modes. Modal diameters and S/Se ratios for samples influenced by northeasterly winds were smaller than those influenced by westerly winds, suggesting a greater age for the latter, despite the close proximity of several large coal-fired power plants to the west of the site. Large peaks in the spectra of S, As, Se, Sb, and V occurred at mass median aerodynamic diameters ranging from 0.3 to 0.6-mu-m in both day and nighttime samples. Simple dispersion estimates suggest that large peaks observed in daytime samples must include material from multiple sources, whereas mass in those observed in nighttime samples could be accounted for by single sources.