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| Titel |
Laboratory studies of immersion and deposition mode ice nucleation of ozone aged mineral dust particles |
| VerfasserIn |
Z. A. Kanji, A. Welti, C. Chou, O. Stetzer, U. Lohmann |
| 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 ; 13, no. 17 ; Nr. 13, no. 17 (2013-09-10), S.9097-9118 |
| Datensatznummer |
250085688
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| Publikation (Nr.) |
 copernicus.org/acp-13-9097-2013.pdf |
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| Zusammenfassung |
| Ice nucleation in the atmosphere is central to the understanding the
microphysical properties of mixed-phase and cirrus clouds. Ambient
conditions such as temperature (T) and relative humidity (RH), as well as
aerosol properties such as chemical composition and mixing state play an
important role in predicting ice formation in the troposphere. Previous
field studies have reported the absence of sulfate and organic compounds on
mineral dust ice crystal residuals sampled at mountain top stations or
aircraft based measurements despite the long-range transport mineral dust is
subjected to. We present laboratory studies of ice nucleation for immersion
and deposition mode on ozone aged mineral dust particles for
233 < T < 263 K. Heterogeneous ice nucleation of untreated kaolinite (Ka)
and Arizona Test Dust (ATD) particles is compared to corresponding aged
particles that are subjected to ozone concentrations of 0.4–4.3 ppmv in a
stainless steel aerosol tank. The portable ice nucleation counter (PINC) and
immersion chamber combined with the Zurich ice nucleation chamber (IMCA-ZINC) are used to conduct deposition and immersion mode
measurements,
respectively. Ice active fractions as well as ice active surface site
densities (ns) are reported and observed to increase as a function of
decreasing temperature. We present first results that demonstrate
enhancement of the ice nucleation ability of aged mineral dust particles in
both the deposition and immersion mode due to ageing. We also present the
first results to show a suppression of heterogeneous ice nucleation activity
without the condensation of a coating of (in)organic material. In immersion
mode, low ozone exposed Ka particles showed enhanced ice activity requiring
a median freezing temperature of 1.5 K warmer than that of untreated Ka,
whereas high ozone exposed ATD particles showed suppressed ice nucleation
requiring a median freezing temperature of 3 K colder than that of untreated
ATD. In deposition mode, low exposure Ka had ice active fractions of an
order of magnitude higher than untreated Ka, whereas high ozone exposed ATD
had ice active fractions up to a factor of 4 lower than untreated ATD. From
our results, we derive and present parameterizations in terms of ns(T)
that can be used in models to predict ice nuclei concentrations based on
available aerosol surface area. |
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