[Zurück]

S. Augustin, S. Hartmann, B. G. Pummer, H. Grothe, D. Niedermeier, T. Clauss, J. Voigtländer, L. Tomsche, H. Wex, F. Stratmann:
"Immersion freezing of birch pollen washing water";
Poster: European Geosciences Union - General Assembly 2013, Wien; 07.04.2013 - 12.04.2013; in: "Geophysical Research Abstracts", 15 (2013).

Up to now, the importance of pollen for atmospheric ice nucleation was considered to be minor, as they are too
large to stay in the atmosphere for a long time. But as recent investigations have shown, not the pollen grains
themselves are responsible for freezing, but easily suspendable macromolecules on their surfaces (Pummer et al.,
2012). Due to the bursting of pollen grains these ice nucleating active (INA) macromolecules could be numerous
in the atmosphere.
In the present study, the immersion freezing behavior of birch pollen, i.e. its ice nucleating active (INA) macromolecules,
was investigated at the Leipzig Aerosol Cloud Interaction Simulator (LACIS, Hartmann et al., 2011).
For this, washing water of two different birch pollen samples with different origin (Northern birch and Southern
birch) were used.
Immersion freezing of droplets generated from the pollen washing water was observed at temperatures higher
than -20 C for both samples. The main difference between the Northern and the Southern birch pollen was the
temperature dependence of the immersion freezing process. Our results suggest that the ice nucleating potential of
the Southern birch is controlled by a single type of INA macromolecule, while the Northern birch pollen seem to
feature two distinctively different types of INA macromolecules.
We determined the heterogeneous nucleation rates for both INA macromolecule types and thereby consistently
describe the ice nucleation behavior of both, the Southern and the Northern birch pollen washing water.
Furthermore we will suggest a theoretical framework for describing e.g. single INA macromolecule related ice
nucleation in atmospheric models.
References:
Pummer, B. G., Bauer, H., Bernardi, J., Bleicher, S. and Grothe, H.: Suspendable macromolecules are responsible
for ice nucleation activity of birch and conifer pollen. Atmos. Chem. Phys., 12, 2541-2550, doi:10.5194/acp-12-
2541-2012, 2012.
Hartmann, S., Niedermeier, D., Voigtländer, J., Clauss, T., Shaw, R. A., Wex, H., Kiselev, A., and Stratmann,
F.: Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies,
Atmos. Chem. Phys., 11, 1753-1767, doi:10.5194/acp-11-1753-2011, 2011.

Ice Nucleation, Bioaerosols, Pollen, Cloud Simulator

http://publik.tuwien.ac.at/files/PubDat_217519.pdf