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| Titel |
Ice nucleation of ammonia gas exposed montmorillonite mineral dust particles |
| VerfasserIn |
A. Salam, U. Lohmann, G. Lesins |
| 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 ; 7, no. 14 ; Nr. 7, no. 14 (2007-07-24), S.3923-3931 |
| Datensatznummer |
250005143
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| Publikation (Nr.) |
 copernicus.org/acp-7-3923-2007.pdf |
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| Zusammenfassung |
| The ice nucleation characteristics of montmorillonite
mineral dust aerosols with and without exposure to ammonia gas were measured
at different atmospheric temperatures and relative humidities with a
continuous flow diffusion chamber. The montmorillonite particles were
exposed to pure (100%) and diluted ammonia gas (25 ppm) at room
temperature in a stainless steel chamber. There was no significant change in
the mineral dust particle size distribution due to the ammonia gas exposure.
100% pure ammonia gas exposure enhanced the ice nucleating fraction of
montmorillonite mineral dust particles 3 to 8 times at 90% relative
humidity with respect to water (RHw) and 5 to 8 times at 100% RHw for 120 min
exposure time compared to unexposed montmorillonite within our
experimental conditions. The percentages of active ice nuclei were 2 to 8
times higher at 90% RHw and 2 to 7 times higher at 100% RHw in 25 ppm
ammonia exposed montmorillonite compared to unexposed montmorillonite. All
montmorillonite particles are more efficient as ice nuclei with increasing
relative humidities and decreasing temperatures. The activation temperature
of montmorillonite exposed to 100% pure ammonia was 15°C higher than
for unexposed montmorillonite particles at 90% RHw. In the 25 ppm ammonia
exposed montmorillonite experiments, the activation temperature was
10°C warmer than unexposed montmorillonite at 90% RHw. Degassing
does not reverse the ice nucleating ability of ammonia exposed
montmorillonite mineral dust particles suggesting that the ammonia is
chemically bound to the montmorillonite particle. This is the first
experimental evidence that ammonia gas exposed montmorillonite mineral dust
particles can enhance its activation as ice nuclei and that the activation
can occur at temperatures warmer than –10°C where natural atmospheric
ice nuclei are very scarce. |
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