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| Titel |
Studies of heterogeneous freezing by three different desert dust samples |
| VerfasserIn |
P. J. Connolly, O. Möhler, P. R. Field, H. Saathoff, R. Burgess, T. Choularton, M. Gallagher |
| 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 ; 9, no. 8 ; Nr. 9, no. 8 (2009-04-27), S.2805-2824 |
| Datensatznummer |
250007214
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| Publikation (Nr.) |
 copernicus.org/acp-9-2805-2009.pdf |
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| Zusammenfassung |
We present results of experiments at the aerosol interactions and
dynamics in the atmosphere (AIDA) chamber facility looking at the
freezing of water by three different types of mineral particles at
temperatures between −12°C and
−33°C. The three different dusts are Asia Dust-1
(AD1), Sahara Dust-2 (SD2) and Arizona test Dust
(ATD). The dust samples used had particle concentrations of sizes
that were log-normally distributed with mode diameters between 0.3 and
0.5 μm and standard deviations, σg, of
1.6–1.9. The results from the freezing experiments are consistent with
the singular hypothesis of ice nucleation. The dusts showed different
nucleation abilities, with ATD showing a rather sharp increase in
ice-active surface site density at temperatures less than
−24°C. AD1 was the next most efficient freezing
nuclei and showed a more gradual increase in activity than the
ATD sample. SD2 was the least active freezing nuclei.
We used data taken with particle counting probes to derive the
ice-active surface site density forming on the dust as a function of
temperature for each of the three samples and polynomial curves are
fitted to this data. The curve fits are then used independently within
a bin microphysical model to simulate the ice formation rates from the
experiments in order to test the validity of parameterising the data
with smooth curves. Good agreement is found between the measurements
and the model for AD1 and SD2; however, the curve for
ATD does not yield results that agree well with the
observations. The reason for this is that more experiments between
−20 and −24°C are needed to quantify the rather
sharp increase in ice-active surface site density on ATD in this
temperature regime. The curves presented can be used as
parameterisations in atmospheric cloud models where cooling rates of
approximately 1°C min−1 or more are present to
predict the concentration of ice crystals forming by the
condensation-freezing mode of ice nucleation. Finally a polynomial is
fitted to all three samples together in order to have
a parameterisation describing the average ice-active surface site
density vs. temperature for an equal mixture of the three dust
samples. |
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