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| Titel |
Heterogeneous freezing of droplets with immersed mineral dust particles – measurements and parameterization |
| VerfasserIn |
D. Niedermeier, S. Hartmann, R. A. Shaw, D. Covert, T. F. Mentel, J. Schneider, L. Poulain, P. Reitz, C. Spindler, T. Clauss, A. Kiselev, E. Hallbauer, H. Wex, K. Mildenberger, F. Stratmann |
| 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. 8 ; Nr. 10, no. 8 (2010-04-19), S.3601-3614 |
| Datensatznummer |
250008360
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| Publikation (Nr.) |
 copernicus.org/acp-10-3601-2010.pdf |
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| Zusammenfassung |
| During the measurement campaign FROST (FReezing Of duST), LACIS
(Leipzig Aerosol Cloud Interaction Simulator) was used to
investigate the immersion freezing behavior of size selected, coated
and uncoated Arizona Test Dust (ATD) particles with a mobility
diameter of 300 nm. Particles were coated with succinic acid
(C4H6O4), sulfuric acid (H2SO4) and ammonium sulfate
((NH4)2SO4). Ice fractions at mixed-phase cloud
temperatures ranging from 233.15 K to 239.15 K (±0.60 K) were
determined for all types of particles. In this temperature range,
pure ATD particles and those coated with C4H6O4 or small
amounts of H2SO4 were found to be the most efficient ice
nuclei (IN). ATD particles coated with (NH4)2SO4 were the
most inefficient IN. Since the supercooled droplets were highly
diluted before freezing occurred, a freezing point suppression due
to the soluble material on the particles (and therefore in the
droplets) cannot explain this observation. Therefore, it is
reasonable to assume that the coatings lead to particle surface
alterations which cause the differences in the IN abilities. Two
different theoretical approaches based on the stochastic and the
singular hypotheses were applied to clarify and parameterize the
freezing behavior of the particles investigated. Both approaches
describe the experimentally determined results, yielding parameters
that can subsequently be used to compare our results to those from
other studies. However, we cannot clarify at the current state which
of the two approaches correctly describes the investigated immersion
freezing process. But both approaches confirm the assumption that
the coatings lead to particle surface modifications lowering the
nucleation efficiency. The stochastic approach interprets the
reduction in nucleation rate from coating as primarily due to an
increase in the thermodynamic barrier for ice formation (i.e.,
changes in interfacial free energies). The singular approach
interprets the reduction as resulting from a reduced surface density
of active sites. |
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