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| Titel |
Hygroscopicity and composition of Alaskan Arctic CCN during April 2008 |
| VerfasserIn |
R. H. Moore, R. Bahreini, C. A. Brock, K. D. Froyd, J. Cozic, J. S. Holloway, A. M. Middlebrook, D. M. Murphy, 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 ; 11, no. 22 ; Nr. 11, no. 22 (2011-11-29), S.11807-11825 |
| Datensatznummer |
250010222
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| Publikation (Nr.) |
 copernicus.org/acp-11-11807-2011.pdf |
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| Zusammenfassung |
| We present a comprehensive characterization of cloud condensation nuclei
(CCN) sampled in the Alaskan Arctic during the 2008 Aerosol, Radiation, and
Cloud Processes affecting Arctic Climate (ARCPAC) project, a component of the
POLARCAT and International Polar Year (IPY) initiatives. Four distinct air
mass types were sampled including a cleaner Arctic background and a
relatively pristine sea ice boundary layer as well as biomass burning and
anthropogenic pollution plumes. Despite differences in chemical composition,
inferred aerosol hygroscopicities were fairly invariant and ranged from
κ = 0.1–0.3 over the atmospherically-relevant range of water vapor
supersaturations studied. Organic aerosols sampled were found to be
well-oxygenated, consistent with long-range transport and aerosol aging
processes. However, inferred hygroscopicities are less than would be
predicted based on previous parameterizations of biogenic oxygenated organic
aerosol, suggesting an upper limit on organic aerosol hygroscopicity above
which κ is less sensitive to the O:C ratio. Most Arctic aerosols act
as CCN above 0.1 % supersaturation, although the data suggest the presence of
an externally-mixed, non-CCN-active mode comprising approximately 0–20% of
the aerosol number. CCN closure was assessed using measured size
distributions, bulk chemical composition, and assumed aerosol
mixing states; CCN predictions tended toward overprediction, with the best
agreement (±0–20 %) obtained by assuming the aerosol to be
externally-mixed with soluble organics. Closure also varied with CCN
concentration, and the best agreement was found for CCN concentrations above
100 cm−3 with a 1.5- to 3-fold overprediction at lower concentrations. |
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