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| Titel |
Laboratory investigations of the impact of mineral dust aerosol on cold cloud formation |
| VerfasserIn |
K. A. Koehler, S. M. Kreidenweis, P. J. DeMott, M. D. Petters, A. J. Prenni, O. Möhler |
| 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 ; 10, no. 23 ; Nr. 10, no. 23 (2010-12-15), S.11955-11968 |
| Datensatznummer |
250008963
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| Publikation (Nr.) |
 copernicus.org/acp-10-11955-2010.pdf |
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| Zusammenfassung |
| Dust particles represent a dominant source of particulate matter (by mass)
to the atmosphere, and their emission from some source regions has been
shown to be transported on regional and hemispherical scales. Dust
particles' potential to interact with water vapor in the atmosphere can lead
to important radiative impacts on the climate system, both direct and
indirect. We have investigated this interaction for several types of dust
aerosol, collected from the Southwestern United States and the Saharan
region. A continuous flow diffusion chamber was operated to measure the ice
nucleation ability of the dust particles in the temperature range of
relevance to cirrus and mixed-phase clouds (−65<T<−20 °C). In
most experiments, particles were size selected using a differential mobility
analyzer prior to sampling to give information on heterogeneity of the
sample with size, generally in the range of diameters 100–400 nm. All dust
nucleated ice heterogeneously in the deposition mode colder than about
−40 °C, but required droplet activation in the exclusively
heterogeneous ice nucleation regime warmer than −36 °C. Ice nucleated on
1% of dry generated dust particles of a given type at a similar relative
humidity with respect to ice irrespective of temperature between −60 and
−40 °C, however differences in relative humidity for ice nucleation
was observed between the different dust types. The Saharan dust types
exhibited a dependency on particle size below 500 nm. Additional data were
collected during the International Workshop on Comparing Ice Nucleation
Measurement Systems (ICIS, 2007) which indicated that ice nucleation on
larger, polydisperse dust particles occurs at warmer temperatures than found
for the smaller particles. When particles were coated with secondary organic
aerosol (SOA) species, higher relative humidity was required for ice
nucleation below −40 °C, similar to that required for homogeneous
nucleation of sulfates. However, ice nucleation was still observed on
SOA-coated dust at warmer temperatures than are required for homogeneous
nucleation of sulfates, indicating that condensation freezing occurs without
any apparent deactivation for temperatures between −25 and −35 °C. |
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