ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-21237-2009 CCN predictions using simplified assumptions of organic aerosol composition and mixing state: a synthesis from six different locations Ervens B. 1 2 Cubison M. J. 1 Andrews E. 1 2 Feingold G. 2 Ogren J. A. 2 Jimenez J. L. 2 3 Quinn P. K. 4 Bates T. S. 4 Wang J. 5 Zhang Q. 6 Coe H. 7 Flynn M. 7 Allan J. D. 8 Cooperative Institute for Research in Environmental Science (CIRES), University of Colorado, Boulder, CO, USA NOAA Earth System Research Laboratory, Boulder, CO, USA Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA NOAA Pacific Marine Environmental Laboratory, Seattle, WA, USA Brookhaven National Laboratory, 75 Rutherford Drive, Upton, NY, USA Department of Environmental Toxicology, University of California, Davis, CA, USA School of Earth, Atmospheric and Environmental Science, The University of Manchester, UK National Centre for Atmospheric Science, School of Earth, Atmospheric & Environmental Sciences, The University of Manchester, Manchester, UK 09 10 2009 9 5 21237 21256 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/9/21237/2009/acpd-9-21237-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/21237/2009/acpd-9-21237-2009.pdf

An accurate but simple quantification of the fraction of aerosol particles that can act as cloud condensation nuclei (CCN) is needed for implementation in large-scale models. Data on aerosol size distribution, chemical composition, and CCN concentration from six different locations have been analyzed to explore the extent to which simple assumptions of composition and mixing state of the organic fraction can reproduce measured CCN number concentrations. <br><br> Fresher pollution aerosol as encountered in Riverside, CA, and the ship channel in Houston, TX, cannot be represented without knowledge of more complex (size-resolved) composition. For aerosol that has experienced processing (Mexico City, Holme Moss (UK), Point Reyes (CA), and Chebogue Point (Canada)), CCN can be predicted within a factor of two assuming either externally or internally mixed soluble organics although these simplified compositions/mixing states might not represent the actual properties of ambient aerosol populations. Under typical conditions, a factor of two uncertainty in CCN concentration translates to an uncertainty of ~15% in cloud drop concentration, which might be adequate for large-scale models given the much larger uncertainty in cloudiness.

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