Apparent freezing temperatures modeled for several experimental apparatus

Abstract

Ice formation by homogeneous nucleation in aqueous atmospheric particles composed of high ionic strength electrolytes is at times believed to be the dominant initiation step in cirrus and polar stratospheric cloud formation. Microphysical models of ice nucleation occurring during atmospheric processes are based upon volume nucleation rates, J(T, x), measured in laboratory experiments where T is temperature and x is mole fraction salt composition. At the present time, there are large discrepancies among apparent freezing temperatures reported by several investigators employing different experimental apparatus. One current hypothesis is that a common J function is expressed differently in these several techniques, which have variations in observation times, system volumes, vapor mass transfer, and so on. In the current paper, we model the several experiments based on a common J function and simulate apparent freezing temperatures of H2SO4/H2O and (NH4)2SO4/H2O particles. We find that the experimental results can be categorized into two groups, one of which is consistent with a function J1 and the other with J2, while J1 and J2 are mutually exclusive. We thus conclude no single J function exists that can simultaneously simulate all reported experimental results, thus refuting the previously proposed "common J" hypothesis for the reconciliation of experimental results. Copyright 2001 by the American Geophysical Union.