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 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.
Citation: Möhler, O., Stetzer, O., Schaefers, S., Linke, C., Schnaiter, M., Tiede, R., Saathoff, H., Krämer, M., Mangold, A., Budz, P., Zink, P., Schreiner, J., Mauersberger, K., Haag, W., Kärcher, B., and Schurath, U.: Experimental investigation of homogeneous freezing of sulphuric acid particles in the aerosol chamber AIDA, Atmos. Chem. Phys., 3, 211-223, doi:10.5194/acp-3-211-2003, 2003.