MASS-PARTICLE SIZE DISTRIBUTIONS OF ATMOSPHERIC DUST AND THE DRY DEPOSITION OF DUST TO THE REMOTE OCEAN

Size-separated mineral aerosol samples were collected and analyzed to investigate the relationships between the mass-particle size distribut ions (MSDs) of dust particles and the dust loadings in the atmosphere, The data also were used to assess the changes in the MSDs of dust in relation to transport processes and especially the associated effects on dry deposition. Atmospheric dust concentrations, as indicated by al uminum or scandium, in samples collected from three sites in the remot e North Atlantic were higher than those in samples collected during a cruise in the North Pacific on board the R/V Moana Wave. However, the mass median diameters (MMDs) for the North Pacific samples were both l arger on average (similar to 3 mu m versus similar to 2 mu m aerodynam ic equivalent diameter) and more variable than those from the North At lantic; this difference was attributed to wet conditions and particle aggregation over the North Pacific. In addition, for the ensemble of a ll samples the geometric standard deviations of the mass-particle size distributions, which are analogous to the sorting values used to char acterize sedimentary materials, tended to vary inversely and nonlinear ly with the mass median diameters. Model-derived dry deposition veloci ties for the samples were at most weakly related to either the dust co ncentrations or the MMDs. However, the dry deposition velocities for t wo subsets of samples were correlated with the geometric standard devi ations of the distributions; this is further evidence that the mass fl ux of dust via dry deposition can be controlled by a relatively small fraction of aerodynamically large particles.