Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies S. Hartmann1, D. Niedermeier1, J. Voigtländer1, T. Clauss1, R. A. Shaw1,2, H. Wex1, A. Kiselev1,3, and F. Stratmann1 1Leibniz Institute for Tropospheric Research, Department of Physics, 04318 Leipzig, Germany 2Michigan Technological University, Department of Physics, Houghton, Michigan 49931, USA 3Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research Atmospheric Aerosol Research Department, 76344 Eggenstein-Leopoldshafen, Germany
Abstract. At the Leipzig Aerosol Cloud Interaction Simulator (LACIS) experiments
investigating homogeneous and heterogeneous nucleation
of ice (particularly immersion freezing in the latter case) have
been carried out. Here both the physical LACIS setup and the numerical
model developed to design experiments at LACIS and interpret their
results are presented in detail.
Combining results from the numerical model with experimental data,
it was found that for the experimental parameter space considered,
classical homogeneous ice nucleation theory is able to predict the
freezing behavior of highly diluted ammonium sulfate solution
droplets, while classical heterogeneous ice nucleation theory,
together with the assumption of a constant contact angle, fails to
predict the immersion freezing behavior of surrogate mineral dust
particles (Arizona Test Dust, ATD). The main reason for this
failure is the compared to experimental data apparently overly
strong temperature dependence of the nucleation rate coefficient.
Assuming, in the numerical model, Classical Nucleation Theory
(CNT) for homogeneous ice nucleation and a CNT-based
parameterization for the nucleation rate coefficient in the
immersion freezing mode, recently published by our group, it was
found that even for a relatively effective ice nucleating agent
such as pure ATD, there is a temperature range where homogeneous
ice nucleation is dominant. The main explanation is the apparently
different temperature dependencies of the two freezing mechanisms.
Finally, reviewing the assumptions made during the derivation of
the CNT-based parameterization for immersion freezing, it was
found that the assumption of constant temperature during ice
nucleation and the chosen ice nucleation time were justified,
underlining the applicability of the method to determine the
fitting coefficients in the parameterization equation.
Citation: Hartmann, S., Niedermeier, D., Voigtländer, J., Clauss, T., Shaw, R. A., Wex, H., Kiselev, A., and Stratmann, F.: Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies, Atmos. Chem. Phys., 11, 1753-1767, doi:10.5194/acp-11-1753-2011, 2011.