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Predicting the Mineral Composition of Dust AerosolsSoil dust aerosols created by wind erosion are typically assigned globally uniform physical and chemical properties within Earth system models, despite known regional variations in the mineral content of the parent soil. Mineral composition of the aerosol particles is important to their interaction with climate, including shortwave absorption and radiative forcing, nucleation of cloud droplets and ice crystals, heterogeneous formation of sulfates and nitrates, and atmospheric processing of iron into bioavailable forms that increase the productivity of marine phytoplankton. Here, aerosol mineral composition is derived by extending a method that provides the composition of a wet-sieved soil. The extension accounts for measurements showing significant differences between the mineral fractions of the wetsieved soil and the emitted aerosol concentration. For example, some phyllosilicate aerosols are more prevalent at silt sizes, even though they are nearly absent at these diameters in a soil whose aggregates are dispersed by wet sieving. We calculate the emitted mass of each mineral with respect to size by accounting for the disintegration of soil aggregates during wet sieving. These aggregates are emitted during mobilization and fragmentation of the original undispersed soil that is subject to wind erosion. The emitted aggregates are carried far downwind from their parent soil. The soil mineral fractions used to calculate the aggregates also include larger particles that are suspended only in the vicinity of the source. We calculate the emitted size distribution of these particles using a normalized distribution derived from aerosol measurements. In addition, a method is proposed for mixing minerals with small impurities composed of iron oxides. These mixtures are important for transporting iron far from the dust source, because pure iron oxides are more dense and vulnerable to gravitational removal than most minerals comprising dust aerosols. A limited comparison to measurements from North Africa shows that the model extensions result in better agreement, consistent with a more extensive comparison to global observations as well as measurements of elemental composition downwind of the Sahara, as described in companion articles.
Document ID
20150023373
Document Type
Reprint (Version printed in journal)
Authors
Perlwitz, J. P. (Columbia Univ. New York, NY, United States)
Garcia-Pando, C. Perez (Columbia Univ. New York, NY, United States)
Miller, R. L. (NASA Goddard Inst. for Space Studies New York, NY, United States)
Date Acquired
December 18, 2015
Publication Date
October 21, 2015
Publication Information
Publication: Atmospheric Chemistry and Physics
Volume: 15
Subject Category
Meteorology and Climatology
Report/Patent Number
GSFC-E-DAA-TN20980
Funding Number(s)
CONTRACT_GRANT: NSF ATM-01-24258
PROJECT: Proj. CGL2011-26259
CONTRACT_GRANT: NNX14AB99A
CONTRACT_GRANT: DE-SC0006713
Distribution Limits
Public
Copyright
Other
Keywords
aerosols
wind erosion
minerals
dust
sediments
iron oxides
soils
iron