Can freeze steel at a great height

Press release

Leipzig, February 11, 2015

Different types of ice nuclei have a major influence on climate in general and precipitation in particular

Leipzig. Mineral and biological particles cause cloud droplets to freeze, so they act as ice nuclei. This is shown by researchers from the Leibniz Institute for Tropospheric Research (TROPOS) with a large number of experiments in the Leipzig cloud laboratory. Of all the mineral dust particles examined, microcline, a frequently occurring mineral from the feldspar group, is the most ice-active. But also biological particles such as parts of pollen and bacteria promote the icing of cloud droplets, according to the studies published in the Geophysical Research Letters and in Atmospheric Chemistry and Physics (ACP), an open access journal of the European Geoscience Union (EGU ), have been published.


In the temperate latitudes, ice crystals played a major role in medium-high clouds between 2000 and 6000m. These mixed-phase clouds consist of both supercooled water droplets and ice crystals. Ice crystals are important in the earth's climate system because they scatter solar and thermal rays differently than liquid water. The formation of ice is also a very important step in the formation of precipitation. Many questions remain unanswered with regard to the formation of ice in clouds and their influence on weather and climate. Science tries to answer these questions with models, field measurements and laboratory tests. This also includes, for example, frequency, size, nature (mineral, organic, biological), as well as other physico-chemical properties of the atmospheric ice nuclei.


The homogeneous ice formation, i.e. the independent freezing of a supercooled water droplet without the aid of an ice nucleus, only takes place in the earth's atmosphere at temperatures below -38 degrees Celsius. If, on the other hand, an aerosol particle is involved in the process, this freezing point is shifted significantly upwards. This heterogeneous ice formation has already been observed in the laboratory at temperatures from -5 degrees Celsius. However, there is a wide range: While some mineral dusts blown up from the ground hardly affect the freezing temperature, Mikroklin allows the water to freeze at temperatures as low as -23 degrees Celsius. The lattice structure on the surface of the mineral probably plays an important role here. However, pollen or bacteria work even better as ice germs: With these, the freezing of water droplets in the Leipzig cloud simulator of TROPOS could be observed from -18 or -8 degrees Celsius. For some time now, a series of experiments on so-called immersion freezing have been carried out there. In immersion freezing, freezing is triggered by an ice nucleus that is located within a supercooled droplet. In contrast, with contact freezing, this process is initiated from the outside by a supercooled drop colliding with a suitable ice nucleus.


The ice nuclei properties of various mineral dusts, volcanic ash and biogenic ice nuclei are the focus of the DFG research group INUIT (Ice Nuclei Research Unit), which is coordinated by the Goethe University in Frankfurt am Main. The investigations in the Leipzig cloud laboratory LACIS are part of a series of tests in various laboratories and field experiments that have been running since 2011. After a successful assessment, the research group was extended for a further 3 years at the end of 2014. The results of the experimental investigations and the new parameterizations derived from them will later be incorporated into models in order to be able to better simulate the description of the clouds and the processes in them. In the most recent report of the Intergovernmental Panel on Climate Change (IPCC), the influence of aerosol particles and clouds is still named as the greatest uncertainty factor in all climate models.

Tilo Arnhold



Augustin-Bauditz, S., H. Wex, S. Kanter, M. Ebert, D. Niedermeier, F. Stolz, A. Prager, and F. Stratmann (2014): The immersion mode ice nucleation behavior of mineral dusts: A. comparison of different pure and surface modified dusts. Geophys. Res. Lett., 41, 7375-7382,

H. Wex, PJ DeMott, Y. Tobo, S. Hartmann, M. Rösch, T. Clauss, L. Tomsche, D. Niedermeier, and F. Stratmann (2014): Kaolinite particles as ice nuclei: learning from the use of different kaolinite samples and different coatings. Atmos. Chem. Phys., 14, 5529-5546,

Niedermeier, D., B. Ervens, T. Clauss, J. Voigtländer, H. Wex, S. Hartmann, and F. Stratmann (2014): A computationally efficient description of heterogeneous freezing: A simplified version of the soccer ball model. Geophys. Res. Lett., 41, 736-741,

Hartmann, S., S. Augustin, T. Clauss, H. Wex, T. Santl Temkiv, J. Voigtländer, D. Niedermeier, and F. Stratmann (2013): Immersion freezing of ice nucleating active protein complexes. Atmos. Chem. Phys., 13, 5751-5766,

Augustin, S., H. Wex, D. Niedermeier, B. Pummer, H. Grothe, S. Hartmann, L. Tomsche, T. Clauss, J. Voigtländer, K. Ignatius, and F. Stratmann (2013): Immersion freezing of birch pollen washing water. Atmos. Chem. Phys., 13, 10989-11003,

These studies were funded by the German Research Association (DFG) as part of the DFG research group INUIT.


Further information:

Leibniz Institute for Tropospheric Research (TROPOS)

Dr. Frank Stratmann / Dr. Heike Wex / Dr. Stefanie Augustin-Bauditz, Tel .: + 49-341-2717-7142, -7146, -7326, / institut / ueber-uns / mitarbeitende / heike-wex / http: //

or Tilo Arnhold, TROPOS Public Relations, Tel. + 49-341-2717-7189



DFG research group INUIT (Ice Nuclei Research Unit) Infrastruktur-technologie/grossforschungsprojekte/inuit/

INUIT at EGU2015: Session AS3.6 "Atmospheric Ice Particles"

"Leipzig Aerosol and Cloud Interaction Simulator" (LACIS) Infrastruktur-technologie/technologie-am-tropos/aerosolversuchsanlagen/lacis/

Investigations on immersion freezing in the LACIS laboratory -in-the-laboratory-and-field / tests-for-immersion-freezing-in-the-laboratory /

TROPOS clouds group:


Cloud simulator Leipzig (Aerosol Cloud Interaction Simulator / LACIS) from the outside. Photo: Tilo Arnhold / TROPOS

Close up of laminar flow tube with laser beam. Photo: Frank Stratmann / TROPOS

Laboratory setup in the Leipzig cloud simulator (Aerosol Cloud Interaction Simulator / LACIS). Photo: Tilo Arnhold / TROPOS