TRACE-ELEMENT LOADING OF SOUTHERN LAKE-MICHIGAN BY DRY DEPOSITION OF ATMOSPHERIC AEROSOL

Aerosol samples and meteorological data were collected at a mid-southern Lake Michigan site (87° 00′ W, 42° 00′ N) from May through September 1977. Hi-volume samplers with cellulose fiber filters and a digital meteorological data recording system were operated on board the U.S. EPA's R/V Roger R. Simons during four intensive sampling periods. Aerosol samples were analyzed by atomic absorption spectroscopy for seventeen trace elements. A diabatic drag coefficient method was used to determine aerosol deposition velocity (vd) overlake. A mean vd of 0.5 cm s-1 was found for the 0.1<diameter<2.0 μm aerosol. By relating the observed trace element concentrations and vd to a long-term climatological record, annual dry deposition loadings to the southern basin for nine elements were estimated. For four elements, Fe, Mn, Pb, and Zn, dry deposition loadings to the southern basin alone of at least 500, 30, 250, and 100 (×103 kg yr-1) were found. For Fe and Mn, these loadings represent about 15% of the total of all inputs to Lake Michigan. for Zn and Pb, about one-third to one-half of the annual loading from all sources is from dry deposition of atmospheric aerosol. © 1979 D. Reidel Publishing Co.