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L. Felgitsch, M. Bichler, T. Häusler, V. Weiss, M. Marchetti-Deschmann, G. Allmaier, H. Grothe:
"Molecular Ice Nucleation Activity of Birch Pollen";
Poster: EGU General Assembly 2015, Vienna; 04-12-2015 - 04-17-2015; in: "Geophysical Research Abstracts", Vol. 17, EGU2015-1560 (2015).

Heterogeneous ice nucleation plays a major part in ecosystem and climate. Due to the triggering of ice cloud
formation it influences the radiation balance of the earth, but also on the ground it can be found to be important
in many processes of nature. So far the process of heterogeneous ice nucleation is not fully understood and many
questions remain to be answered. Biological ice nucleation is hereby from great interest, because it shows the
highest freezing temperatures. Several bacteria and fungi act as ice nuclei. A famous example is
Pseudomonas
syringae
, a bacterium in commercial use (Snomax®), which increases the freezing from homogeneous freezing
temperatures of approx. -40 ̊C (for small volumes as in cloud droplets) to temperatures up to -2 ̊C. In 2001 it was
found that birch pollen can trigger ice nucleation (Diehl et al. 2001; Diehl et al. 2002). For a long time it was
believed that this is due to macroscopic features of the pollen surface. Recent findings of Bernhard Pummer (2012)
show a different picture. The ice nuclei are not attached on the pollen surface directly, but on surface material
which can be easily washed off. This shows that not only the surface morphology, but also specific molecules or
molecular structures are responsible for the ice nucleation activity of birch pollen.
With various analytic methods we work on elucidating the structure of these molecules as well as the mechanism
with which they trigger ice nucleation. To solve this we use various instrumental analytic techniques like Nu-
clear Magnetic Resonance spectroscopy (NMR), Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry
(MALDI-MS), and Gas-phase Electrophoretic Mobility Molecular Analysis (GEMMA). Also standard techniques
like various chromatographic separation techniques and solvent extraction are in use.
We state here that this feature might be due to the aggregation of small molecules, with agglomerates showing
a specific surface structure. Our results indicate that the substance is amphiphilic in character leading finally to
micelle formation.
Diehl, K., Quick, C., Matthias-Maser, S., Mitra, S. K., and Jaenicke, R.: The ice nucleation ability of pollen, part
I, Atmos. Res., 58, 75-87, 2001.
Diehl, K., Matthias-Maser, S., Jaenicke, R., and Mitra, S. K.: The ice nucleation ability of pollen, part II, Atmos.
Res., 61, 125-133, 2002.
Pummer, B., Bauer, H., Bernardi, J., Bleicher, S., Grothe, H.; Suspendable macromolecules are responsible for ice
nucleation activity of birch and conifer pollen; Atmos. Chem. Phys., 12, 2541 - 2550, 2012.

heterogeneous ice nucleation

http://publik.tuwien.ac.at/files/PubDat_243408.pdf