ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-5663-2010 Surfactants in cloud droplet activation: mixed organic-inorganic particles Prisle N. L. 1 4 Raatikainen T. 2 Laaksonen A. 2 3 Bilde M. 4 University of Helsinki, Department of Physics, P.O. Box 48, 00014, University of Helsinki, Finland Finnish Meteorological Institute, Erik Palmenin Aukio 1, 00101, Helsinki, Finland University of Kuopio, Department of Physics, P.O. Box 1627, 70211, Kuopio, Finland University of Copenhagen, Department of Chemistry, Universitetsparken 5, 2100, Copenhagen, Denmark 29 06 2010 10 12 5663 5683 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.net/10/5663/2010/acp-10-5663-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/5663/2010/acp-10-5663-2010.pdf

Organic compounds with surfactant properties are commonly found in atmospheric aerosol particles. Surface activity can significantly influence the cloud droplet forming ability of these particles. We have studied the cloud droplet formation by two-component particles comprising one of the organic surfactants sodium octanoate, sodium decanoate, sodium dodecanoate, and sodium dodecyl sulfate, mixed with sodium chloride. Critical supersaturations were measured with a static diffusion cloud condensation nucleus counter (Wyoming CCNC-100B). Results were modeled from Köhler theory applying three different representations of surfactant properties in terms of surfactant surface partitioning and reduced droplet surface tension. We here confirm previous results for single-component organic surfactant particles, that experimental critical supersaturations are greatly underpredicted, if reduced surface tension is used while ignoring the effects of surface partitioning in droplets. Furthermore, disregarding surfactant properties by ignoring surface partitioning and assuming the constant surface tension of pure water can also lead to significant underpredictions of experimental critical supersaturations. For the mixed particles comprising less than 50% by mass of surfactant, this approach however still provides a good description of the observed droplet activation. A comprehensive account for surfactant properties, including both surface tension reduction and effects of surface partitioning in activating droplets, generally predicts experimental critical supersaturations well.

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