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| Titel |
Importance of aerosol composition and mixing state for cloud droplet activation over the Arctic pack ice in summer |
| VerfasserIn |
C. Leck, E. Svensson |
| 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 ; 15, no. 5 ; Nr. 15, no. 5 (2015-03-06), S.2545-2568 |
| Datensatznummer |
250119501
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| Publikation (Nr.) |
 copernicus.org/acp-15-2545-2015.pdf |
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| Zusammenfassung |
| Concentrations of cloud condensation nuclei (CCN) were measured throughout
an expedition by icebreaker around the central Arctic Ocean, including a
3 week ice drift operation at 87° N, from 3 August to 9 September 2008.
In agreement with previous observations in the area and season, median
daily CCN concentrations at 0.2% water vapour supersaturation (SS) were
typically in the range of 15 to 30 cm−3, but concentrations varied by
2 to 3 orders of magnitude over the expedition and were occasionally
below 1 cm−3. The CCN concentrations were highest near the ice edge and
fell by a factor of 3 in the first 48 h of transport from the open
sea into the pack ice region. For longer transport times they increased
again, indicating a local source over the pack ice, suggested to be polymer
gels, via drops injected into the air by bubbles bursting on open leads. We
inferred the properties of the unexplained non-water soluble aerosol
fraction that was necessary for reproducing the observed concentrations of
CCN. This was made possible by assuming Köhler theory and simulating the
cloud nucleation process using a Lagrangian adiabatic air parcel model that
solves the kinetic formulation for condensation of water on size resolved
aerosol particles. We propose that the portion of the internally/externally
mixed water insoluble particles was larger in the corresponding smaller
aerosol size ranges. These particles were physically and chemically
behaving as polymer gels: the interaction of the hydrophilic and hydrophobic
entities on the structures of polymer gels during cloud droplet activation
would at first only show a partial wetting character and only weak
hygroscopic growth. Given time, a high CCN activation efficiency is
achieved, which is promoted by the hydrophilicity or surface-active
properties of the gels. Thus the result in this study argues that the
behaviour of the high Arctic aerosol in CCN-counters operating at water vapour
SSs > 0.4% (high relative humidities) may not be
properly explained by conventional Köhler theory. |
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