Influence of the ice growth rate on the incorporation of gaseous HCl

Ice crystals were grown in the laboratory at -15degreesC, at different growth rates and in the presence of a partial pressure of HCl of 1.63 x 10(-3) Pa, to test whether the ice growth rate influences the amount of HCl taken up, X-HCl, as predicted by the ice growth mechanism of Domine and Thibert (1996). The plot of HCl concentration in ice as a function of growth rate has the aspect predicted by that mechanism: X-HCl decreases with increasing growth rate, from a value that depends on thermodynamic equilibrium to a value that depends only on kinetic factors. The height of the growth steps of the ice crystals is determined to be about 150 nm from these experiments. We discuss that the application of these laboratory experiments to cloud ice crystals and to snow metamorphism is not quantitatively possible at this stage, because the physical variables that determine crystal growth in nature, and in particular the step height, are not known. Qualitative applications are attempted for HCl and HNO3 incorporation in cloud ice and snowpack crystals.