Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 7 2 2007 10.5194/acp-7-309-2007 http://www.atmos-chem-phys.net/7/309/2007/ http://www.atmos-chem-phys.net/7/309/2007/acp-7-309-2007.html http://www.atmos-chem-phys.net/7/309/2007/acp-7-309-2007.pdf 309 313 2007-01-19 Technical Note: The heterogeneous Zeldovich factor H. Vehkamäki hanna.vehkamaki@helsinki.fi A. Määttänen A. Lauri I. Napari M. Kulmala Department of Physical Sciences, Division of Atmospheric Sciences, University of Helsinki, Helsinki, Finland In this technical note we present the exact form of the Zeldovich factor for heterogeneous nucleation on spherical pre-existing particles. We study the error caused by planar pre-existing surface approximations, which have been used in our earlier heterogeneous nucleation model and elsewhere in the literature. We also test the significance of widely used approximations for cluster surface area and circumference. We conclude that the approximations do not affect the predicted onset saturation. Especially for small pre-existing particles the nucleation rates calculated with the exact and approximative models differ significantly. Laaksonen, A., McGraw, R., and Vehkamäki, H.: Liquid-drop formalism and free-energy surfaces in binary homogeneous nucleation theory, J. Chem. Phys., 111, 2019–2027, 1999. Määttänen, A., Vehkamäki, H., Lauri, A., Merikallio, S., Kauhanen, J., Savijärvi, H., and Kulmala, M.: Nucleation studies in the Martian atmosphere, J. Geophys. Res., 110, E02002, doi:10.1029/2004JE002308, 2005. Ono, S. and Kondo, S.: Encyclopedia of Physics, p. 134, Springer, Berlin, 1960. Pruppacher, H R. and Klett, J D.: Microphysics of Clouds and Precipitation, Kluwer Acad., Norwell, Mass., 1997.