Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 5 2005 10.5194/acpd-5-8507-2005 http://www.atmos-chem-phys-discuss.net/5/8507/2005/ http://www.atmos-chem-phys-discuss.net/5/8507/2005/acpd-5-8507-2005.html http://www.atmos-chem-phys-discuss.net/5/8507/2005/acpd-5-8507-2005.pdf 8507 8646 2005-09-12 The effect of physical and chemical aerosol properties on warm cloud droplet activation G. McFiggans P. Artaxo U. Baltensperger H. Coe M. C. Facchini G. Feingold S. Fuzzi M. Gysel A. Laaksonen U. Lohmann T. F. Mentel D. M. Murphy C. D. O’Dowd J. R. Snider E. Weingartner Atmospheric Sciences Group, SEAES, University of Manchester, PO Box 88, Manchester, M60 1QD, UK Instituto de Fisica, Universidade de Sao Paulo, Rua do Matao, Travessa R, 187, CEP 05508-900 Sao Paulo, Brazil Paul Scherrer Institut, Labor für Atmosphärenchemie, 5232 Villigen PSI, Switzerland Istituto di Scienze dell’Atmosfera e del Clima, CNR, 40129 Bologna, Italy NOAA Environmental Technology Laboratory, 325 Broadway, Boulder, Colorado 80305, USA Department of Applied Physics, University of Kuopio, PO Box 1627, 70211 Kuopio, Finland Institute for Atmospheric and Climate Science, Schafmattstr. 30, ETH Zurich, 8093 Zurich, Switzerland Forschungszentrum Jülich GmbH, ICG-II: Troposphäre, D-52425 Jülich, Germany NOAA Aeronomy Laboratory, 325 Broadway, Boulder, Colorado 80305, USA Department of Physics, National University of Ireland, Galway, Ireland University of Wyoming, Department of Atmospheric Science, Laramie, WY 82071, USA no affiliation The effects of atmospheric aerosol on climate forcing may be very substantial but are quantified poorly at present; in particular, the effects of aerosols on cloud radiative properties, or the "indirect effects" are credited with the greatest range of uncertainty amongst the known causes of radiative forcing. This manuscript explores the effects that the composition and properties of atmospheric aerosol can have on the activation of droplets in warm clouds, so potentially influencing the magnitude of the indirect effect. The effects of size, composition, mixing state and various derived properties are assessed and a range of these properties provided by atmospheric measurements in a variety of locations is briefly reviewed. The suitability of a range of process-level descriptions to capture these aerosol effects is investigated by assessment of their sensitivities to uncertainties in aerosol properties and by their performance in closure studies. The treatment of these effects within global models is reviewed and suggestions for future investigations are made.