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| Titel |
Parameterization of cloud droplet formation for global and regional models: including adsorption activation from insoluble CCN |
| VerfasserIn |
P. Kumar, I. N. Sokolik, A. Nenes |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 7 ; Nr. 9, no. 7 (2009-04-07), S.2517-2532 |
| Datensatznummer |
250007166
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| Publikation (Nr.) |
 copernicus.org/acp-9-2517-2009.pdf |
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| Zusammenfassung |
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.
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 R2~0.98. 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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