Importance of fine particle loading to fluxes of trace elements dry depositing onto Lake Michigan

Abstract

Size segregated aerosol samples were collected with a micro orifice impactor at three sites to characterize fine particle deposition of urban aerosol from the Chicago area to Lake Michigan. Samples collected at two shoreline sites of Lake Michigan and aboard the EPA Research Vessel Lake guardian on Lake Michigan and aboard the EPA Research Vessel Lake Guardian on Lake Michigan were analyzed for > 40 elements using x-ray fluorescence and instrumental neutron activation analysis. Anthropogenic elements such as S and Ni are concentrated on fine accumulation mode aerosol particles having a geometric mass mean aerodynamic diameter (GMMAD) of 0.46 mm, while K, Fe, Mn, and Ca are primarily associated with coarse particles having a modal diameter of 6.9 mm. Samples collected during prevailing westerly winds from Chicago show rapidly decreasing concentrations of crustal elements as the plume moves across the Lake from Chicago to South haven while S concentrations are seen to increase, presumably reflecting SO{sub 2} conversion to sulfate aerosol; Ni concentrations remain relatively constant. Fine particles, on which many toxic anthropogenic pollutants are concentrated, are predicted to have lower dry deposition velocities, but are seen here to influence much larger areas of the Lake. Fluxes calculated for elementsmore » in urban aerosol transported across the lake using modeled dry deposition velocities show fine particle deposition fluxes comparable to those for coarse particles for some important elements.« less