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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 3, issue 1
Atmos. Chem. Phys., 3, 211-223, 2003
https://doi.org/10.5194/acp-3-211-2003
© Author(s) 2003. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.
Atmos. Chem. Phys., 3, 211-223, 2003
https://doi.org/10.5194/acp-3-211-2003
© Author(s) 2003. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  20 Feb 2003

20 Feb 2003

Experimental investigation of homogeneous freezing of sulphuric acid particles in the aerosol chamber AIDA

O. Möhler1, O. Stetzer1, S. Schaefers1, C. Linke1, M. Schnaiter1, R. Tiede1, H. Saathoff1, M. Krämer2, A. Mangold2, P. Budz3, P. Zink3, J. Schreiner3, K. Mauersberger3, W. Haag4, B. Kärcher4, and U. Schurath1 O. Möhler et al.
  • 1Forschungszentrum Karlsruhe (FZK), Institute of Meteorology and Climate Research (IMK-AAF), Karlsruhe, Germany
  • 2Forschungszentrum Jülich (FZJ), Institut für Chemie und Dynamik der Geosphäre (ICG-1), Jülich, Germany
  • 3Max-Planck-Institut für Kernphysik (MPIK), Abteilung Atmosphärenphysik, Heidelberg, Germany
  • 4Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre (IPA), Oberpfaffenhofen, Germany

Abstract. The homogeneous freezing of supercooled H2SO4/H2O solution droplets was investigated in the aerosol chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) of Forschungszentrum Karlsruhe. 24 freezing experiments were performed at temperatures between 189 and 235 K with aerosol particles in the diameter range 0.05 to 1 µm. Individual experiments started at homogeneous temperatures and ice saturation ratios between 0.9 and 0.95. Cloud cooling rates up to -2.8 K min-1 were simulated dynamically in the chamber by expansion cooling using a mechanical pump. Depending on the cooling rate and starting temperature, freezing threshold relative humidities were exceeded after expansion time periods between about 1 and 10 min. The onset of ice formation was measured with three independent methods showing good agreement among each other. Ice saturation ratios measured at the onset of ice formation increased from about 1.4 at 231 K  to about 1.75 at 189 K. The experimental data set including thermodynamic parameters as well as physical and chemical aerosol analysis provides a good basis for microphysical model applications.

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