ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-22041-2009 Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM Croft B. 1 Lohmann U. 2 Martin R. V. 1 3 Stier P. 4 Wurzler S. 5 Feichter J. 6 Hoose C. 7 Heikkilä U. 8 van Donkelaar A. 1 Ferrachat S. 2 Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada Institute of Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland Harvard-Smithsonian Center for Astrophysics, Cambridge, USA Atmospheric, Oceanic, and Planetary Physics, University of Oxford, Oxford, UK Landesamt fur Umwelt, Natur und Verbraucherschutz NRW (LANUV), Recklinghausen, Germany Max Planck Institute for Meteorology, Hamburg, Germany Department of Geosciences, University of Oslo, Oslo, Norway Bjerknes Centre for Climate Research, Bergen, Norway 21 10 2009 9 5 22041 22101 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/9/22041/2009/acpd-9-22041-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/22041/2009/acpd-9-22041-2009.pdf

A diagnostic nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. Sensitivity studies are presented, which compare aerosol concentrations, and deposition between a variety of in-cloud scavenging approaches, including prescribed fractions, several diagnostic schemes, and a prognostic aerosol cloud processing treatment that passes aerosol in-droplet and in-ice crystal concentrations between model time steps. For one sensitivity study, assuming 100% of the in-cloud aerosol is scavenged into the cloud droplets and ice crystals, the annual global mean accumulation mode number burden is decreased by 65%, relative to a simulation with prognostic aerosol cloud processing. Diagnosing separate nucleation scavenging ratios for aerosol number and mass distributions, as opposed to equating the aerosol mass scavenging to the number scavenging ratios, reduces the annual global mean sulfate burden by near to 10%. The annual global mean sea salt burden is 30% lower for the diagnostic approach, which does not carry aerosol in-droplet and in-crystal concentrations between model time-steps as compared to the prognostic scheme. Implementation of in-cloud impaction scavenging reduced the annual, global mean black carbon burden by 30% for the prognostic aerosol cloud processing scheme. Better agreement with observations of black carbon profiles from aircraft (changes near to one order of magnitude for mixed phase clouds), <sup>210</sup>Pb surface layer concentrations and wet deposition, and the geographic distribution of aerosol optical depth are found for the new diagnostic scavenging as compared to prescribed ratio scavenging scheme of the standard ECHAM5-HAM.

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