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| Titel |
Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site |
| VerfasserIn |
N. C. Shantz, R. Y.-W. Chang, J. G. Slowik, A. Vlasenko, J. P. D. Abbatt, W. R. Leaitch |
| 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 ; 10, no. 1 ; Nr. 10, no. 1 (2010-01-15), S.299-312 |
| Datensatznummer |
250007907
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| Publikation (Nr.) |
 copernicus.org/acp-10-299-2010.pdf |
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| Zusammenfassung |
| Growth rates of water droplets were measured with a static diffusion cloud
condensation chamber in May–June 2007 at a rural field site in Southern
Ontario, Canada, 70 km north of Toronto. The observations include periods
when the winds were from the south and the site was impacted by
anthropogenic air from the U.S. and Southern Ontario as well as during a
5-day period of northerly wind flow when the aerosol was dominated by
biogenic sources. The growth of droplets on anthropogenic size-selected
particles centred at 0.1 μm diameter and composed of approximately
40% organic and 60% ammonium sulphate (AS) by mass, was delayed by on
the order of 1 s compared to a pure AS aerosol. Simulations of the
growth rate on monodisperse particles indicate that a lowering of the water
mass accommodation coefficient from αc=1 to an average of αc=0.04 is
needed (assuming an insoluble organic with hygroscopicity parameter,
κorg, of zero). Simulations of the initial growth rate on polydisperse
anthropogenic particles agree best with observations for αc=0.07. In
contrast, the growth rate of droplets on size-selected aerosol of biogenic character,
consisting of >80% organic, was similar to that of pure AS. Simulations
of the predominantly biogenic polydisperse aerosol show agreement between
the observations and simulations when κorg=0.2 (with upper and lower
limits of 0.5 and 0.07, respectively) and αc=1. Inhibition of water
uptake by the anthropogenic organic applied to an adiabatic cloud parcel
model in the form of a constant low αc increases the number of droplets
in a cloud compared to pure AS. If the αc is assumed to increase with
increasing liquid water on the droplets, then the number of droplets
decreases which could diminish the indirect climate forcing effect. The
slightly lower κorg in the biogenic case decreases the number of
droplets in a cloud compared to pure AS. |
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