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| Titel |
Investigating the discrepancy between wet-suspension- and dry-dispersion-derived ice nucleation efficiency of mineral particles |
| VerfasserIn |
C. Emersic, P. J. Connolly, S. Boult, M. Campana, Z. Li |
| 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. 19 ; Nr. 15, no. 19 (2015-10-12), S.11311-11326 |
| Datensatznummer |
250120091
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| Publikation (Nr.) |
 copernicus.org/acp-15-11311-2015.pdf |
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| Zusammenfassung |
| Cloud chamber investigations into ice nucleation by mineral particles were
compared with results from cold-stage droplet freezing experiments.
Kaolinite, NX-illite, and K-feldspar were examined, and K-feldspar was
revealed to be the most ice-active mineral particle sample, in agreement with
recent cold-stage studies. The ice nucleation efficiencies, as quantified
using the ice-active surface site density method, were found to be
in agreement with previous studies for the lower temperatures; however, at
higher temperatures the efficiency was between a factor of 10 and 1000 higher
than those inferred from cold-stage experiments. Numerical process modelling
of cloud formation during the experiments, using the cold-stage-derived
parameterisations to initiate the ice phase, revealed the cold-stage-derived
parameterisations to consistently underpredict the number of ice crystals
relative to that observed. We suggest the reason for the underestimation of
ice in the model is that the slope of the cold-stage-derived
ice-active surface site density vs. temperature curves are too steep,
which results in an underestimation of the number of ice crystals at higher
temperatures during the expansion. These ice crystals suppress further
freezing due to the Bergeron–Findeison process. A coagulation model was used
to investigate the idea that the mineral particles coagulate in suspension.
This model suggests that coagulation during the experiments may be sufficient
to significantly remove the particles for the suspension by sedimentation or
reduce the total particle surface area available for ice nucleation to take
place. Aggregation was confirmed to take place in mineral suspensions using
dynamic light-scattering measurements. However, it is not proven that
aggregation of the mineral particles is able to reduce the surface area
available for ice nucleation. The implication is that the mineral particles
may be more important at nucleating ice at high temperatures than previously
thought. |
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