WET DEPOSITION IN A GLOBAL SIZE-DEPENDENT AEROSOL TRANSPORT MODEL 2 -INFLUENCE OF THE SCAVENGING SCHEME ON PB-210 VERTICAL PROFILES, SURFACE CONCENTRATIONS, AND DEPOSITION

The main atmospheric sink for submicron aerosols is wet removal. Lead 210, the radioactive decay product of Rn-222, attaches immediately aft er being formed to submicron particles. Here we compare the effects of three different wet-scavenging schemes used in global aerosol simulat ions on the (210)pb aerosol distribution using an off-line, size-resol ved, global atmospheric transport model. We highlight the merits and s hortcomings of each scavenging scheme at reproducing available measure ments, which include concentrations in surface air and deposition, as well as vertical profiles observed over North America and western and central North Pacific. We show that model-measurement comparison of to tal deposition does not allow to distinguish between scavenging scheme s because compensation effects can hide the differences in their respe ctive scavenging efficiencies. Differences in scavenging parameterizat ion affect the aerosol vertical distribution to a much greater extent than the surface concentration. Zonally averaged concentrations at dif ferent altitudes derived from the model vary by more than a factor of 3 according to the scavenging formulation, and only one scheme enables us to reproduce reliably the individual profiles observed. This study shows that ground measurements alone are insufficient to validate a g lobal aerosol transport model.