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- ItemInfluence of cloud processing on CCN activation behaviour in the Thuringian Forest, Germany during HCCT-2010(München : European Geopyhsical Union, 2014) Henning, S.; Dieckmann, K.; Ignatius, K.; Schäfer, M.; Zedler, P.; Harris, E.; Sinha, B.; van Pinxteren, D.; Mertes, S.; Birmili, W.; Merkel, M.; Wu, Z.; Wiedensohler, A.; Wex, H.; Herrmann, H.; Stratmann, F.Within the framework of the "Hill Cap Cloud Thuringia 2010" (HCCT-2010) international cloud experiment, the influence of cloud processing on the activation properties of ambient aerosol particles was investigated. Particles were probed upwind and downwind of an orographic cap cloud on Mt Schmücke, which is part of a large mountain ridge in Thuringia, Germany. The activation properties of the particles were investigated by means of size-segregated cloud condensation nuclei (CCN) measurements at 3 to 4 different supersaturations. The observed CCN spectra together with the total particle spectra were used to calculate the hygroscopicity parameter κ for the upwind and downwind stations. The upwind and downwind critical diameters and κ values were then compared for defined cloud events (FCE) and non-cloud events (NCE). Cloud processing was found to increase the hygroscopicity of the aerosol particles significantly, with an average increase in κ of 50%. Mass spectrometry analysis and isotopic analysis of the particles suggest that the observed increase in the hygroscopicity of the cloud-processed particles is due to an enrichment of sulfate and possibly also nitrate in the particle phase.
- ItemImmersion freezing of birch pollen washing water(München : European Geopyhsical Union, 2013) Augustin, S.; Wex, H.; Niedermeier, D.; Pummer, B.; Grothe, H.; Hartmann, S.; Tomsche, L.; Clauss, T.; Voigtländer, J.; Ignatius, K.; Stratmann, F.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.