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| Titel |
Particle surface area dependence of mineral dust in immersion freezing mode: investigations with freely suspended drops in an acoustic levitator and a vertical wind tunnel |
| VerfasserIn |
K. Diehl, M. Debertshäuser, O. Eppers, H. Schmithüsen, S. K. Mitra, S. Borrmann |
| 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 ; 14, no. 22 ; Nr. 14, no. 22 (2014-11-25), S.12343-12355 |
| Datensatznummer |
250119183
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| Publikation (Nr.) |
 copernicus.org/acp-14-12343-2014.pdf |
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| Zusammenfassung |
| The heterogeneous freezing temperatures of supercooled drops were measured
using an acoustic levitator. This technique allows one to freely suspend single
drops in the air without any wall contact. Heterogeneous nucleation by two
types of illite (illite IMt1 and illite NX) and a montmorillonite sample was
investigated in the immersion mode. Drops of 1 mm in radius were monitored
by a video camera while cooled down to −28 °C to simulate
freezing within the tropospheric temperature range. The surface temperature
of the drops was contact-free, determined with an infrared thermometer; the
onset of freezing was indicated by a sudden increase of the drop surface
temperature. For comparison, measurements with one particle type (illite
NX) were additionally performed in the Mainz vertical wind tunnel with drops
of 340 μm radius freely suspended. Immersion freezing was observed in
a temperature range between
−13 and −26 °C as a function of
particle type and particle surface area immersed in the drops. Isothermal
experiments in the wind tunnel indicated that after the cooling stage
freezing still proceeds, at least during the investigated time period of 30 s. The results were evaluated by applying two descriptions of heterogeneous
freezing, the stochastic and the singular model. Although the wind tunnel
results do not support the time-independence of the freezing process both
models are applicable for comparing the results from the two experimental
techniques. |
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