Airborne concentrations and dry deposition fluxes of particulate species to surrogate surfaces deployed in southern Lake Michigan

Dry deposition flux measurements to surrogate surfaces and airborne concentration measurements of Zn-containing; S-rich, and soil particles (analyzed by scanning electron microscopy) and Al, Ba, Br, Ca, Cl, Cu, K, Mg, Mn, Na, Ti, and V (analyzed by neutron activation analysis) were made over southwestern Lake Michigan in July 1994 and January 1995 to determine atmospheric inputs of pollutants to the lake. Samples collected in the summer show that despite relatively low airborne concentrations of particles with physical diameters >8 μm, these particles account for the majority of the dry deposition mass flux. However, this sharp contrast is not found during January when particles with physical diameters of 4-8 μm dominate both the airborne concentration and the flux. Dry deposition velocities (flux divided by airborne concentration) for particles are found to range from 0.0062 cm/s for 0.75-μm particles to 5.4 cm/s for 24-μm particles.