Characterization of the optical properties of irregular mineral dust aggregates combining individual particle analysis and modeling

Mineral aerosol presents a particularly difficult case in climate and remote sensing studies, because its absorption and scattering of atmospheric radiation depend strongly on dust source region, morphology (i.e. shape and size), mineralogy, and state of mixture with other species. We are developing a technique to model optical properties of dust particles and their mixtures that makes use of data provided by the individual-particle methods (such as chemically distinct inorganic particle type, the degree of aggregation of the distinct particle species, two dimensional shape and size of each dry particle). We apply this technique to dust samples collected in Phoenix (dust in the urban polluted environment) and Bermuda (dust in the marine environment) to characterize peculiar dust optical properties in these geographical regions. The individual-particle analysis of these samples was carried out at Arizona State University, employing automated scanning electron microscopy and transmission electron microscopy.Employing these data, we model optical properties using the discrete-dipole approximation (DDA) technique. We perform numerous calculations for nonspherical versus spherical particles to examine the effect of morphology/composition on dust optical properties. We focus on the analysis of the single scattering albedo and the scattering phase function needed for climate modeling and remote sensing applications.