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| Titel |
Experimental quantification of contact freezing in an electrodynamic balance |
| VerfasserIn |
N. Hoffmann, A. Kiselev, D. Rzesanke, D. Duft, T. Leisner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 9 ; Nr. 6, no. 9 (2013-09-12), S.2373-2382 |
| Datensatznummer |
250085062
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| Publikation (Nr.) |
 copernicus.org/amt-6-2373-2013.pdf |
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| Zusammenfassung |
| Heterogeneous nucleation of ice in a supercooled water droplet induced by
external contact with a dry aerosol particle has long been known to be more
effective than freezing induced by the same nucleus immersed in the droplet.
However, the experimental quantification of contact freezing is challenging.
Here we report an experimental method to determine the temperature-dependent
ice nucleation probability of size-selected aerosol particles. The method is
based on the suspension of supercooled charged water droplets in a laminar
flow of air containing aerosol particles as contact freezing nuclei. The rate
of droplet–particle collisions is calculated numerically with account for
Coulomb attraction, drag force and induced dipole interaction between charged
droplet and aerosol particles. The calculation is verified by direct counting
of aerosol particles collected by a levitated droplet. By repeating the
experiment on individual droplets for a sufficient number of times, we are
able to reproduce the statistical freezing behavior of a large ensemble of
supercooled droplets and measure the average rate of freezing events. The
freezing rate is equal to the product of the droplet–particle collision
rate and the probability of freezing on a single contact, the latter being a
function of temperature, size and composition of the contact ice nuclei.
Based on these observations, we show that for the types of particles
investigated so far, contact freezing is the dominating freezing mechanism on
the timescale of our experiment. |
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