ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-2517-2009 Parameterization of cloud droplet formation for global and regional models: including adsorption activation from insoluble CCN Kumar P. 1 Sokolik I. N. 2 Nenes A. 1 2 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 07 04 2009 9 7 2517 2532 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/9/2517/2009/acp-9-2517-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/2517/2009/acp-9-2517-2009.pdf

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>i</i>) find combinations of the adsorption parameters <i>A</i><sub>FHH</sub>, <i>B</i><sub>FHH</sub> which yield atmospherically-relevant behavior, and, <i>ii</i>) express activation properties (critical supersaturation) that follow a simple power law with respect to dry particle diameter. <br><br> The new parameterization is tested by comparing the parameterized cloud droplet number concentration against predictions with a detailed numerical cloud model, considering a wide range of particle populations, cloud updraft conditions, water vapor condensation coefficient and FHH adsorption isotherm characteristics. The agreement between parameterization and parcel model is excellent, with an average error of 10% and <i>R</i><sup>2</sup>~0.98. A preliminary sensitivity study suggests that the sublinear response of droplet number to Köhler particle concentration is not as strong for FHH particles.

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