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Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM

Roelofs, G. J. and Stier, P. and Feichter, J. and Vignati, E. and Wilson, J. (2006) Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM. Atmospheric Chemistry and Physics, 6 (9). pp. 2389-2399. ISSN 1680-7316.

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A parameterization for cloud processing is presented that calculates activation of aerosol particles to cloud drops, cloud drop size, and pH-dependent aqueous phase sulfur chemistry. The parameterization is implemented in the global aerosol-climate model ECHAM5-HAM. The cloud processing parameterization uses updraft speed, temperature, and aerosol size and chemical parameters simulated by ECHAM5-HAM to estimate the maximum supersaturation at the cloud base, and subsequently the cloud drop number concentration (CDNC) due to activation. In-cloud sulfate production occurs through oxidation of dissolved SO2 by ozone and hydrogen peroxide. The model simulates realistic distributions for annually averaged CDNC although it is underestimated especially in remote marine regions. On average, CDNC is dominated by cloud droplets growing on particles from the accumulation mode, with smaller contributions from the Aitken and coarse modes. The simulations indicate that in-cloud sulfate production is a potentially important source of accumulation mode sized cloud condensation nuclei, due to chemical growth of activated Aitken particles and to enhanced coalescence of processed particles. The strength of this source depends on the distribution of produced sulfate over the activated modes. This distribution is affected by uncertainties in many parameters that play a direct role in particle activation, such as the updraft velocity, the aerosol chemical composition and the organic solubility, and the simulated CDNC is found to be relatively sensitive to these uncertainties.

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Additional Information:© 2006 Author(s). This work is licensed under a Creative Commons License. Received: 20 October 2005 – Published in Atmos. Chem. Phys. Discuss.: 12 January 2006 Revised: 15 May 2006 – Accepted: 16 May 2006 – Published: 29 June 2006 The study contributes to the EU project PHOENICS (“Particles of Human Origin Extinguish Natural solar Irradiance in the Climate System”; EVK2-CT-2001-00098). We thank SARA Reken- en Netwerkdiensten in Amsterdam for use of their supercomputer and acknowledge the use of the Ferret program for the graphics (
Issue or Number:9
Record Number:CaltechAUTHORS:ROEacp06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3965
Deposited By: Archive Administrator
Deposited On:20 Jul 2006
Last Modified:02 Oct 2019 23:08

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