As part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS) the dry deposition fluxes and atmospheric size distributions (ASDs) of anthropogenic metals were measured over the southern basin of Lake Michigan. The measurements were made during winter, summer, and fall, concurrently, in Chicago, IL; over Lake Michigan onboard the U.S. EPA RV Lake Guardian; and in South Haven, MI. The flux of Pb, Cu, and Zn was substantially higher in Chicago than in either South Haven or over Lake Michigan. The average measured Pb, Cu, and Zn fluxes were 0.07, 0.06, and 0.20 mg m -2 day -1 in Chicago; 0.003, 0.01, and 0.01 mg m -2 day -1 over Lake Michigan; and 0.004, 0.007, and 0.004 mg m -2 day -1 in South Haven. When the wind was from Chicago over the lake, the fluxes and concentrations measured over the lake were higher than when the wind was from other directions. In general, these anthropogenic metals had higher concentrations in the fine particle mode than in the coarse particle mode. Modeled and measured fluxes were in reasonable agreement. Coarse particles were found to be responsible for the majority of the flux at all locations.

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ABSTRACT. In this study, which was a part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS) investigation, the dry deposition fluxes and atmospheric size distributions (ASDs) of mass and crustal metals (aluminum and magnesium) were measured over the southern basin of Lake Michigan (in Chicago, over Lake Michigan, and in South Haven, Michigan). Airborne crustal metals arise primarily from fugitive dust emissions and are associated with the coarse fraction of atmospheric aerosol. Consequently, they can serve as fingerprints for the atmospheric behavior of fugitive dust. The flux of these metals were substantially higher in Chicago than in either South Haven or over Lake Michigan. The measured average mass, aluminum, and magnesium fluxes were 138,2.23, and 5.32 mg/m2-day in Chicago, 47.8, 0.24, and 0.28 mg/m2-day over Lake Michigan, and 37.4, 0.17, and 0.12 mg/m2-day in South Haven, respectively. The ASDs of crustal metals measured in Chicago had higher concentrations of coarse particles than ASDs measured over Lake Michigan and in South Haven. The calculated flux of metals using a multistep model and dry deposition velocities obtained from the Sehmel-Hodgson model were in general agreement with measured fluxes of crustal metals. Particles >10 pm were found to be responsible for the majority of the flux. AEROSOL SCIENCE AND TECH-

ABSTRACT. Long-term dry deposition and dichotomous coarse particle samples were collected between November 1993 and October 1995 in Chicago, IL, as part of ( ) the Lake Michigan Mass Balance Study LMMBS . In addition, short-term dry ( ) deposition and airborne coarse particle Noll Rotary Impactor samples were collected during the Atmospheric Exch ange Over Lakes and Oceans Study ( ) AEOLOS . These samples were an alyzed for trace metals an d modeled using the ( ) ( ) U.S. EPA's Chemical Mass Balance CMB Model Version 7 to determine the sources of these particles. The modeled source contributions were similar. The results indicate that light duty unleaded vehicles, soil dust, and heavy duty diesel vehicles were the major sources of ambient coarse and dry deposited particles in Ch icago. The other sources found were lime kilns, coke dust, aluminum foundryreverberatory furnace, coal-® red power plant, paint spray booth, and municipal incineration. The results from this study indicate that the CMB approach can be used to determine the source of deposited particles.