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F. Stratmann, H. Wex, D. Niedermeier, S. Hartmann, S. Augustin, T. Clauss, J. Voigtländer, B. G. Pummer, H. Grothe:
"Ice nucleation rates of single protein complexes and single macromolecules";
Poster: AGU Fall Meeting 2012, San Francisco; 12-03-2012 - 12-07-2012; in: "2012 Fall Meeting, AGU", (2012), A13I-0297.

With our flow-tube LACIS (Leipzig Aerosol cloud Interaction Simulator), we measured immersion freezing of droplets containing biological ice nucleating (IN) agents. From our measurements, we were able to deduce ice nucleation rates for single IN protein complexes (for Snomax) and for IN macromolecules (in the case of Birch pollen). For the measurements, aerosol particles were produced from solutions/suspensions of either Snomax (deadened and partly fractionalized pseudomonas syringae bacteria) or of Birch pollen washing water (BW in the following). All particles were dried and size selected before entering LACIS. In LACIS, particles were activated to droplets, and we measured the fraction of all droplets that froze (F(ice)) as function of temperature. For Snomax, a strong increase in F(ice) was observed around -7 to -10 °C, for BW around -19 to -25 °C, respectively. After this initial steep increase, F(ice) stayed constant for both examined substances down to -35 °C. We found that the values of F(ice) in the plateau region depended on the dry particle size. The initial solution used to generate the particles contained parts of bacteria with ice active protein complexes on them in the case of Snomax, or IN macromolecules in the case of BW (Pummer et al., 2011). We show that the distribution of the IN proteins or IN molecules in the aerosol particles follows the Poisson distribution. With this knowledge, derivation of the ice nucleation rates for single IN protein complexes or for single IN macromolecules is possible. Combining the Poisson distribution with a stochastic model and using the derived nucleation rates, we can reproduce not only our measurements for both examined substances, but also past measurements done for Snomax and even pseudomonas syringae bacteria. As an additional peculiarity, we seem to observe two different macromolecules being ice active for Birch trees growing in Central Europe or Northern Europe, with the latter initiating freezing at slightly warmer temperatures. Pummer, B. G. et al. (2012), Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen, Aerosol Chem. Phys., 12, 2541-2550.

Ice Nucleation, Bioaerosols, Poisson Distribution

http://fallmeeting.agu.org/2012/eposters/eposter/a13i-0297/