Atmos. Chem. Phys. Discuss., 8, 12721-12736, 2008
© Author(s) 2008. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Cloud processing, cloud evaporation and Angström exponent
G.-J. Roelofs and V. Kamphuis
Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands

Abstract. With a cloud parcel model we investigated how cloud processing and cloud evaporation modify the size distribution and the Angström exponent of an aerosol population. Cloud processing causes a decrease in particle concentrations, relatively most efficiently in the coarse mode, and reduces the relative dispersion of the aerosol distribution. As a result the Angström exponent of the aerosol increases. The Angström exponent is subject to other influences. It is very sensitive for relative humidity, especially between 95% and 100%. In addition, kinetic limitations delay droplet evaporation during cloud dissipation, which hampers a direct relation between the Angström exponent and the relative humidity. Consequently, a direct interpretation of the Angström exponent in terms of aerosol properties that play a role in aerosol-cloud interactions, such as the fine mode fraction, is rather complex.

Citation: Roelofs, G.-J. and Kamphuis, V.: Cloud processing, cloud evaporation and Angström exponent, Atmos. Chem. Phys. Discuss., 8, 12721-12736, doi:10.5194/acpd-8-12721-2008, 2008.
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