[Zurück]

S. Augustin, S. Hartmann, B. G. Pummer, H. Grothe, D. Niedermeier, T. Clauss, J. Voigtländer, L. Tomsche, H. Wex, F. Stratmann:
"Ice nucleation rates of single protein complexes and single macromolecules";
Vortrag: ESF-Workshop - Atmospheric Ice Nucleation, Wien (eingeladen); 06.04.2013 - 07.04.2013; in: "Workshop - Atmospheric Ice Nucleation - Book of Abstracts", (2013).

Biological particles, such as some bacteria and pollen species, are known to nucleate ice at much higher temperatures than non-biological particles, e.g. mineral dust. In the case of bacteria, ice nucleation active (INA) protein complexes connected to the bacteria´s outer
membrane are controlling the ice nucleation. Pollen feature INA macromolecules which induce ice nucleation (Pummer et al., 2012). For the investigation of the immersion freezing behavior of these biological ice nucleating entities, we performed measurements with sizeselected particles generated from a SNOMAX® solution/suspension in water, and birch pollen washing water (BW in the following), at the laminar diffusion chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator, Hartmann et al., 2011). Ice fractions were measured, as function of temperature and number of INA entities, i.e., either INA protein complexes or INA macromolecules.
For SNOMAX®, which is an artificial product consisting of pseudomonas syringe bacteria, we found immersion freezing already to occur at temperatures around -7 °C. In the case of BW we observed freezing at temperatures slightly higher than -20°C. After an initial steep increase with decreasing temperature, the ice fraction stayed constant (saturation behavior) down to -35°C, for both examined materials. Based on this saturation behavior we were able to show, that the distribution of entities over the droplet ensemble follows a Poisson distribution. Using the so-called CHESS (stoCHastic modEl of similar poiSSon distributed ice nuclei, Hartmann et al., 2012) model, a combination of the Poisson distribution and a simple stochastic nucleation approach, the derivation of the ice nucleation rates for both, single INA protein complexes and single INA macromolecules are possible. The determined nucleation rates together with a reasonable number of INA entities can be used for describing biological IN agents related ice nucleation in atmospheric models. As an additional peculiarity, we observed two different INA macromolecules for Birch trees growing in central Europe and Northern Europe, with the latter initiating freezing at slightly higher temperatures.

ice nucleation, pollen, bacteria, flow tube