Physico-chemical parameters of mixed mineral, biomass burning and marine aerosols

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Over large deserts, mineral (and other components) dust is produced by natural processes and man-made activity. Once injected into the atmosphere, dust is mixed with other natural components like biogenic material, evaporated cloud droplets, and anthropogenic components like sulfates and soot. This airborne dust is transported long distances. The interaction of desert aerosols with atmospheric processes strongly depends on a variety of physico-chemical parameters as a function of particle size and the spatial distribution and transformation during their atmospheric residence time. Optical dust parameters, size and spatial distribution of these desert aerosols determine the direct interaction of solar and IR-radiation in the atmosphere through scattering and absorption. Bulk and surface chemistry of the dust material determines the potential to be incorporated into the formation of precipitation, which is responsible for additional indirect effects. Because of the large extent of such deserts (30% of the continents), a worldwide influence has been observed. This project focuses on mesurements of the physico-chemical properties of desert aerosol particles. The investigations consist of two major parts. (1): Laboratory investigtions on size-resolved composition of desert soil samples in order to determine optical parameters from mineral and non-mineral components using samples of the "Mainz Sandbank", (2): Actual measurements of the size and spatial distribution and composition of airborne dust over the desert during a joint field campaign (closure experiment) in Morocco. An improved data set provides by this project will be the basis for more realistic model simulations of the transport of dust and its effect on the radiation field.