Size dependence of volume and surface nucleation rates for homogeneous freezing of supercooled water droplets 1Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, Canada
*now at: Division of Space Technology, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Kiruna, Sweden
**now at: Cloud Physics and Severe Weather Research Section, Environment Canada, Toronto, ON, Canada
***now at: Department of Atmospheric Sciences, Texas A&M University, College Station, TX, USA
Received: 28 Aug 2009 – Published in Atmos. Chem. Phys. Discuss.: 28 Oct 2009Abstract. The relative roles of volume and surface nucleation were
investigated for the homogeneous freezing of pure water droplets.
Experiments were carried out in a cryogenic laminar aerosol flow
tube using supercooled water aerosols with
maximum volume densities at radii between
1 and 3 μm. Temperature- and size-dependent values of volume-
and surface-based homogeneous nucleation rates between 234.8 and
236.2 K were derived using a microphysical model and aerosol phase
compositions and size distributions determined from infrared
extinction measurements in the flow tube. The results show that the
contribution from nucleation at the droplet surface increases with
decreasing droplet radius and dominates over nucleation in the bulk
droplet volume for droplets with radii smaller than approximately
5 μm. This is interpreted in terms of a lowered free energy of
ice germ formation in the surface-based process. The implications of
surface nucleation for the parameterization of homogeneous ice
nucleation in numerical models are considered.
Revised: 10 Mar 2011 – Accepted: 21 Mar 2011 – Published: 28 Mar 2011
Citation: Kuhn, T., Earle, M. E., Khalizov, A. F., and Sloan, J. J.: Size dependence of volume and surface nucleation rates for homogeneous freezing of supercooled water droplets, Atmos. Chem. Phys., 11, 2853-2861, doi:10.5194/acp-11-2853-2011, 2011.