ATMOCHEM - Biological aerosol particles in the atmosphere and their impact on clouds (BIOCLOUDS)
Zusammenfassung der Projektergebnisse
Aerosol particles are essential for the formation of both liquid water clouds and ice clouds, thus playing a key role in atmospheric sciences and climate. Some of these aerosol particles are of biological origin, for example plant debris, pollen or living organisms like bacteria, fungi and yeasts, which have been detected in cloud water and melted snow. The aim of the BIOCLOUDS project was to investigate how aerosol particles of biological origin act as cloud condensation nuclei (CCN) and ice nuclei (IN) in the atmosphere. This objective was achieved in close collaboration with the French project partners from the Blaise Pascal University in Clermont-Ferrand who isolated bacterial strains from cloud water sampled at Puy-de-Dôme, pre-checked them for their ice-nucleating potential, and cultured the most active strains for detailed CCN and IN viability experiments at the Bielefeld University and the AIDA cloud chamber at the Karlsruhe Institute of Technology (KIT). The viability of bacterial cell in the aerosol state was also measured and the ice nucleation activity of different pollen particles was also measured in both labs not only to check for the consistency of IN results from the different labs and methods, but also to get new results as input for model runs with the COSMO-ART model of KIT. Together with associated partners from the University of Mainz, the ETH Zurich, the PSI in Villigen, and the TROPOS institute in Leipzig, the laboratory experiments within BIOCLOUDS were complemented by a comprehensive characterisation of the bacterial cells with electron microscopy and aerosol mass spectrometry and by IN measurements of size-selected particles sampled from the KIT aerosol and cloud chambers. The major findings of the project can be summarized as follows: The ice nucleation ability of non-viable bacteria and of pollen samples immersed in water is rather insensitive to the addition of solutes or changes in pH. In fact, the solute effect upon onset freezing temperature can be parameterized using a water-activity-based ice nucleation approach. This type of parameterization is suitable for application in atmospheric cloud models as well as for describing ice nucleation in freeze tolerant beetles or living insect larvae. Bacterial cells first immersed in water and then dispersed into the aerosol phase show a steeply increasing immersion freezing activity in a narrow temperature range between about -5 and -8°C. The ice nucleation activity reaches an almost constant value at temperatures below about -10°C. Only a minor fraction of all cells is ice-active, and there is a large variability of the ice-nucleation activity for different bacterial species isolated from cloud water. The same cells are ice-active in the immersion freezing and deposition nucleation modes. The bacterial cells keep their viability and ice nucleation activity when residing in the aerosol phase at low temperature for several hours. Birch, sunflower and hazelnut pollen were found to be ice-active at temperatures below about -15°C, with an ice-active particle fraction close to one below about -20°C. There was good agreement for the results of ice nucleation experiments with the same birch pollen samples performed at the Bielefeld University and KIT. First COSMO-ART model runs performed for a model domain over Europe showed that, on average, pollen may play a role as INP only in the boundary layer, about 1 to 2 km above the Earth’s surface, whereas at higher altitude in the free troposphere, the INP abundance is by far dominated by INP of mineral dust origin.
Projektbezogene Publikationen (Auswahl)
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Parameterizations for ice nucleation in biological and atmospheric systems, Phys. Chem. Chem. Phys., 11(46), 10839–50, 2009
Koop, T. and Zobrist, B.
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Effects of atmospheric conditions on ice nucleation activity of Pseudomonas, Atmos. Chem. Phys., 12(22), 10667–10677, 2012
Attard, E., Yang, H., Delort, A.-M., Amato, P., Pöschl, U., Glaux, C., Koop, T. and Morris, C. E.
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Einzelpartikel- und Ensemblemessungen mit dem Aerosolmassenspektrometer (AMS): Untersuchungen zu Quellen und chemischer Zusammensetzung von Aerosolpartikeln im Submikrometerbereich, Dissertation, Johannes Gutenberg-Universität Mainz, 2012
Freutel, F.
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Laboratory studies with cloud-derived Bacterial Cells acting as Ice Nuclei in the Immersion and Deposition Mode, in: EGU General Assembly, Geophysical Research Abstracts Vol. 14, EGU2012-399, Vienna, Austria, 2012
Oehm, C. E., Chou, C., Amato, P., Attard, E., Delort, A.-M., Morris, C., Kiselev, A., Stetzer, O., Möhler, O., and Leisner, T.
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(2013), The contribution of biological aerosols to atmospheric ice nucleation, in: Nucleation and Atmospheric Aerosols: 19th International Conference, (eds.: P. J. DeMott, C. O’Dowd), AIP Conference Proceedings, 1527, 899, Fort Collins, Colorado, USA, 2013
Hummel, M., Hoose, C., Möhler, O., Oehm, C. E., Steinke, I., and Vogel, H.
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Atmospheric science: The seeds of ice in clouds, Nature, 498(7454), 302- 303, 2013
Koop, T. and Mahowald, N.
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Investigation of heterogeneous ice nucleation using a novel optical freezing array, in: Nucleation and Atmospheric Aerosols 2013 (Eds.: P.J. DeMott and C.D. O'Dowd), AIP Conference Proceedings, 1527, 949-951, 2013
Budke, C., Dreischmeier, K., Pedernera, D.A., Dreyer, A., Koop, T.
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Parameterizations of ice formation derived from AIDA cloud simulation experiments, in: Nucleation and Atmospheric Aerosols: 19th International Conference, (eds.: P. J. DeMott, C. O’Dowd), AIP Conference Proceedings, 1527, 851, Fort Collins, Colorado, USA, 2013
Möhler, O., Hiranuma, N., Höhler, K., Hoose, C., Hummel, M., Niemand, M., Oehm, C. E., Schmitt, T., Steinke, I., and Wagner, R.
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Untersuchungen zur Rolle von Bakterien und Pollen als Wolkenkondensations- und Eiskeime in troposphärischen Wolken, Dissertation, Ruprecht Karls-Universität Heidelberg, 2013
Schaupp, C. E.
