References

ACPD

Atmospheric Chemistry and Physics Discussions

ACPD

1680-7375

Copernicus GmbH

Göttingen, Germany

10.5194/acpd-9-22929-2009

Size dependence of volume and surface nucleation rates for homogeneous freezing of supercooled water droplets

Kuhn

¹ ² Earle

M. E.

¹ ³ Khalizov

A. F.

¹ ⁴ Sloan

J. J.

Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, Canada

now at: Department of Space Science, Luleå Technical University, 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

28 10 2009

9 5 22929 22953

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

This article is available from http://www.atmos-chem-phys-discuss.net/9/22929/2009/acpd-9-22929-2009.html

The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/22929/2009/acpd-9-22929-2009.pdf

We investigated the relative roles of volume and surface nucleation in the freezing of water droplets. Nucleation experiments were carried out in a cryogenic laminar aerosol flow tube using supercooled liquid water aerosols with radii between about 1 and 3 μ m. Temperature- and size-dependent values of volume- and surface-based homogeneous nucleation rate between 234.8 and 236.2 K are derived with help of a microphysical model from aerosol compositions and size distributions based on infrared extinction measurements in the aerosol 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 and has implications for the parameterization of homogeneous ice nucleation in numerical models.

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