HR: 1340h
AN: A53A-0157    [Abstracts]
TI: Radiative Properties and Climate Forcing Potential of Ammonium-Sulfate and Nitrate Coated Mineral Dust Particles
AU: * Bauer, S E
EM: sbauer@giss.nasa.gov
AF: NASA/GISS Columbia University, 2880 Broadway, New York, NY 10025 United States
AB: Heterogeneous chemical reactions between sulfate and nitrate precursors on the surface of mineral dust aerosols affect the atmospheric aerosol cycle and the earth radiation budget. Heterogeneous reactions of sulfur dioxide with mineral dust particles enhance sulfate formation, producing sulfate coatings on dust particles. Reactions between NOx species, especially nitric acid, and mineral dust lead to mixed nitrate dust particles. These mixed particles consists of a hydrophilic core, mineral dust, and a hygroscopic shell, sulfate and/or nitrate. Calculations of optical properties of such particles show that the single-scattering albedo of core-mantle aerosols can be expressed as a linear combination of the single-scattering albedos of pure dust and pure pollutant particles having the same size as the composite aerosol. However, the asymmetry parameter of the composite particles can be significantly lower than the asymmetry parameter of either pure aerosol. Global simulations, of pre-industrial and current day climate performed with the Goddard Institute for Space Studies GCM, of sulfate/nitrate coated dust particles show that the thickness of the shell can be expected to range from 0 to 20% of the radius of the dust core. Theoretical calculations suggest that the radiative effect of composite aerosols with coating layers thinner than 20% of the core diameter should differ negligibly from that of uncoated dust particles. Sulfate and nitrate coatings on mineral dust particles, change the aerosol load of the single aerosol species, causing a positive anthropogenic forcing of 0.3 W/m2 due to less coating at pre-industrial times. Although, the magnitude of this forcing is extremely uncertain (e.g. as a result of the unknown solubility dependence of dust particles on coatings) we point out that the sign of this anthropogenic forcing is positive.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005