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| Titel |
Immersion freezing of birch pollen washing water |
| VerfasserIn |
S. Augustin, H. Wex, D. Niedermeier, B. Pummer, H. Grothe, S. Hartmann, L. Tomsche, T. Clauss, J. Voigtländer, K. Ignatius, F. Stratmann |
| 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. 21 ; Nr. 13, no. 21 (2013-11-11), S.10989-11003 |
| Datensatznummer |
250085807
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| Publikation (Nr.) |
 copernicus.org/acp-13-10989-2013.pdf |
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| Zusammenfassung |
| Birch pollen grains are known to be ice nucleating active biological particles. The
ice nucleating activity has previously been tracked down to biological
macromolecules that can be easily extracted from the pollen grains in water.
In the present study, we investigated the immersion freezing behavior of
these ice nucleating active (INA) macromolecules. Therefore we measured the
frozen fractions of particles generated from birch pollen washing water as a
function of temperature at the Leipzig Aerosol Cloud Interaction Simulator
(LACIS). Two different birch pollen samples were considered, with one
originating from Sweden and one from the Czech Republic. For the Czech and Swedish birch pollen samples, freezing was observed to start at
−19 and −17 °C, respectively. The fraction of frozen
droplets increased for both samples down to −24 °C. Further cooling
did not increase the frozen fractions any more. Instead, a plateau formed at
frozen fractions below 1. This fact could be used to determine the amount of
INA macromolecules in the droplets examined here, which in turn allowed for
the determination of nucleation rates for single INA macromolecules. The main
differences between the Swedish birch pollen and the Czech birch pollen were
obvious in the temperature range between −17 and
−24 °C. In this range, a second plateau region could be seen for
Swedish birch pollen. As we assume INA macromolecules to be the reason for
the ice nucleation, we concluded that birch pollen is able to produce at
least two different types of INA macromolecules. We were able to derive
parameterizations for the heterogeneous nucleation rates for both INA
macromolecule types, using two different methods: a simple exponential fit
and the Soccer ball model. With these parameterization methods we were able to
describe the ice nucleation behavior of single INA macromolecules from both
the Czech and the Swedish birch pollen. |
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