Thermodynamics of homogeneous nucleation of ice particles in the polar summer mesosphere A. Y. Zasetsky1, S. V. Petelina2,3, and I. M. Svishchev1 1Trent University, Peterborough, Ontario, Canada 2La Trobe University, Victoria, Australia 3Formerly at the University of Saskatchewan, Saskatoon, Canada
Abstract. We present the hypothesis of homogeneous nucleation of ice nano-particles in
the polar summer mesosphere. The nucleation of condensed phase is traced
back to the first step on the formation pathway, which is assumed to be the
transition of water vapor to amorphous cluster. Amorphous clusters then
freeze into water ice, likely metastable cubic ice, when they reach the
critical size. The estimates based on the equilibrium thermodynamics give
the critical size (radius) of amorphous water clusters as about 1.0 nm. The
same estimates for the final transition step, that is the transformation of
cubic to hexagonal ice, give the critical size of about 15 nm at typical
upper mesospheric conditions during the polar summer (temperature T=150 K,
water vapor density ρvapor=109 cm−3).
Citation: Zasetsky, A. Y., Petelina, S. V., and Svishchev, I. M.: Thermodynamics of homogeneous nucleation of ice particles in the polar summer mesosphere, Atmos. Chem. Phys., 9, 965-971, doi:10.5194/acp-9-965-2009, 2009.