DEPOSITION OF TRACE-METALS IN URBAN AND RURAL-AREAS IN THE LAKE-MICHIGAN BASIN

Ambient concentrations measured in Chicago and in the rural area of Kankakee (Illinois) are presented for a wide range of trace metals associated with fine (<2.5 mum) and coarse (2.5-10 mum) particles. Elements typically of crustal origin in the fine fraction were detected at similar concentrations in both sites. However, crustal elements in the coarse fraction were found three to fifteen times higher than that associated with fine fraction in both sites. Elements primarily of anthropogenic origin were found in similar concentrations in Chicago and Kankakee, except for elements such as Cr which was detected at levels three to four times higher in Kankakee. Meteorological parameters, particle size distribution and surface characteristics are considered in a dynamic model for calculating the deposition velocity for each particle size. The deposition velocities for fine particles is in the range from 0.25 to 0.46 cm/s in Chicago and from 0.18 to 0.25 cm/s in Kankakee, while for coarse particles the range is from 1.47 to 2.93 cm/s in Chicago and from 0.87 to 1.71 cm/s in Kankakee. The deposition fluxes in Chicago are usually highest, except for Al which is deposited at highest rates in Kankakee in both the fine 4.6 mug/m2-h and coarse 250 mug/m2-h fraction. Finally, estimates of the total amount of trace metals accumulated on paved areas and potentially discharged into the sewer systems by storm water run-off in the urban and rural area are discussed.