ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-24717-2009 Comprehensively accounting for the effect of giant CCN in cloud droplet activation parameterizations Barahona D. 1 West R. E. L. 3 Stier P. 3 Romakkaniemi S. 4 Kokkola H. 5 Nenes A. 1 2 School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, USA School of Earth and Atmospheric Sciences, Georgia Institute of Technology, USA Atmospheric, Oceanic and Planetary Physics, Department of Physics, University\newline of Oxford, UK Department of Physics, University of Kuopio, Finland Finnish Meteorological Institute, Kuopio Unit, Finland 18 11 2009 9 6 24717 24730 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/9/24717/2009/acpd-9-24717-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/24717/2009/acpd-9-24717-2009.pdf

Cloud droplet activation parameterizations used in aerosol indirect effect assessments often assume that droplet growth after activation is much greater than their equilibrium size close to cloud base. This assumption does not hold for large CCN which may experience limited growth. If a large fraction of the aerosol is composed of such particles (such as regions with large fractions of dust particles and seasalt), neglecting such kinetic limitations in cloud droplet activation parameterizations leads to an underestimation of droplet surface area during cloud formation, hence overestimation of maximum supersaturation and cloud droplet number. Here we present a simple approach to address this problem and that can easily be incorporated into cloud droplet activation parameterizations. A demonstration of this method is done for activation parameterizations based on the ''population splitting'' concept of Nenes and Seinfeld (2003).

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