HR: 10:30h
AN: A72B-01 INVITED     [Abstracts]
TI: Hygroscopicity of mineral dust particles: Roles of chemical mixing state and hygroscopic conversion timescale
AU: * Sullivan, R C
EM: rsullivan@atmos.colostate.edu
AF: Department of Atmospheric Science, Colorado State University, Campus Delivery 1371, Fort Collins, CO 80523, United States
AU: * Sullivan, R C
EM: rsullivan@atmos.colostate.edu
AF: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
AU: Moore, M J
EM: moore@ucsd.edu
AF: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
AU: Petters, M D
EM: petters@atmos.colostate.edu
AF: Department of Atmospheric Science, Colorado State University, Campus Delivery 1371, Fort Collins, CO 80523, United States
AU: Laskin, A
EM: Alexander.Laskin@pnl.gov
AF: Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richlans, WA 99352, United States
AU: Roberts, G C
EM: greg@fiji.ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
AU: Kreidenweis, S M
EM: sonia@atmos.colostate.edu
AF: Department of Atmospheric Science, Colorado State University, Campus Delivery 1371, Fort Collins, CO 80523, United States
AU: Prather, K A
EM: kprather@ucsd.edu
AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
AU: Prather, K A
EM: kprather@ucsd.edu
AF: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
AB: Our laboratory investigations of mineral dust particle hygroscopicity are motivated by field observations of the atmospheric processing of dust. During ACE-Asia we observed sulphate and nitrate to be strongly segregated from each other in individual aged Asian dust particles. CCN activation curves of pure calcium minerals as proxies for fresh (calcium carbonate) and aged (calcium sulphate, nitrate, chloride) dust indicate that this mixing state would cause a large fraction of aged dust particles to remain poor warm cloud nucleation potential, contrary to previous assumptions. The enrichment of oxalic acid in calcium-rich dust particles could have similar effects due to the formation of insoluble calcium oxalate. Soluble calcium nitrate and chloride reaction products are hygroscopic and will transform mineral dust into excellent CCN. Generating insoluble mineral particles wet by atomization produced particles with much higher hygroscopicity then when resuspended dry. The atomized particles are likely composed of dissolved residuals and do not properly reflect the chemistry of dry mineral powders. Aerosol flow tube experiments were employed to study the conversion of calcium carbonate into calcium nitrate via heterogeneous reaction with nitric acid, with simultaneous measurements of the reacted particles' chemistry and hygroscopicity. The timescale for this hygroscopic conversion was found to occur on the order of a few hours under tropospheric conditions. This implies that the conversion of non-hygroscopic calcite- containing dust into hygroscopic particles will be controlled by the availability of nitric acid, and not by the atmospheric residence time. Results from recent investigations of the effect of secondary coatings on the ice nucleation properties of dust particles will also be presented. The cloud formation potential of aged dust particles depends on both the quantity and form of the secondary species that have reacted or mixed with the dust. These results have important implications for the treatment of mineral dust particles in global chemistry and climate models.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2009 Joint Assembly