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| Titel |
Tight coupling of particle size, number and composition in atmospheric cloud droplet activation |
| VerfasserIn |
D. O. Topping, G. McFiggans |
| 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 ; 12, no. 7 ; Nr. 12, no. 7 (2012-04-04), S.3253-3260 |
| Datensatznummer |
250011010
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| Publikation (Nr.) |
 copernicus.org/acp-12-3253-2012.pdf |
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| Zusammenfassung |
The substantial uncertainty in the indirect effect of aerosol particles on
radiative forcing in large part arises from the influences of atmospheric
aerosol particles on (i) the brightness of clouds, exerting significant
shortwave cooling with no appreciable compensation in the long wave, and on
(ii) their ability to precipitate, with implications for cloud cover and
lifetime.
Predicting the ambient conditions at which aerosol particles may become cloud
droplets is largely reliant on an equilibrium relationship derived by
Köhler (1936). However, the theoretical basis of the relationship
restricts its application to particles solely comprising involatile compounds
and water, whereas a substantial fraction of particles in the real atmosphere
will contain potentially thousands of semi-volatile organic compounds in
addition to containing semi-volatile inorganic components such as ammonium
nitrate.
We show that equilibration of atmospherically reasonable concentrations of
organic compounds with a growing particle as the ambient humidity increases
has potentially larger implications on cloud droplet formation than any other equilibrium
compositional dependence, owing to inextricable linkage between the aerosol
composition, a particles size and concentration under ambient conditions.
Whilst previous
attempts to account for co-condensation of gases other than water vapour have
been restricted to one inorganic condensate, our method demonstrates that
accounting for the co-condensation of any number of organic compounds
substantially decreases the saturation ratio of water vapour required for
droplet activation. This effect is far greater than any other compositional
dependence; more so even than the unphysical effect of surface tension
reduction in aqueous organic mixtures, ignoring differences in bulk and
surface surfactant concentrations. |
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