Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 7 2009 10.5194/acp-9-2517-2009 http://www.atmos-chem-phys.net/9/2517/2009/ http://www.atmos-chem-phys.net/9/2517/2009/acp-9-2517-2009.html http://www.atmos-chem-phys.net/9/2517/2009/acp-9-2517-2009.pdf 2517 2532 2009-04-07 Parameterization of cloud droplet formation for global and regional models: including adsorption activation from insoluble CCN P. Kumar I. N. Sokolik A. Nenes nenes@eas.gatech.edu School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, 30332, USA School of Earth and Atmospheric Sciences, Georgia Institute of Technology Atlanta, GA, 30332, USA Dust and black carbon aerosol have long been known to exert potentially important and diverse impacts on cloud droplet formation. Most studies to date focus on the soluble fraction of these particles, and overlook interactions of the insoluble fraction with water vapor (even if known to be hydrophilic). To address this gap, we developed a new parameterization that considers cloud droplet formation within an ascending air parcel containing insoluble (but wettable) particles externally mixed with aerosol containing an appreciable soluble fraction. Activation of particles with a soluble fraction is described through well-established Köhler theory, while the activation of hydrophilic insoluble particles is treated by "adsorption-activation" theory. In the latter, water vapor is adsorbed onto insoluble particles, the activity of which is described by a multilayer Frenkel-Halsey-Hill (FHH) adsorption isotherm modified to account for particle curvature. We further develop FHH activation theory to i) find combinations of the adsorption parameters AFHH, BFHH which yield atmospherically-relevant behavior, and, ii) express activation properties (critical supersaturation) that follow a simple power law with respect to dry particle diameter. 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