HR: 1340h
AN: A53B-1155    [Abstracts]
TI: Molecular transport and phase transition of polycrystalline ice doped with HCl and SO2 near its melting point
AU: * Lu, H
EM: haiping@gwu.edu
AF: the George Washington University, Chemistry Department Corcoran Hall 725 21st Street, NW, Washington, DC 20052, United States
AU: McCartney, S
EM: steph116@gwu.edu
AF: the George Washington University, Chemistry Department Corcoran Hall 725 21st Street, NW, Washington, DC 20052, United States
AU: Sadtchenko, V
EM: vlad@gwu.edu
AF: the George Washington University, Chemistry Department Corcoran Hall 725 21st Street, NW, Washington, DC 20052, United States
AB: HCl and SO2 are major trace gases in atmosphere, which greatly affects chemical properties of atmospheric ice particles. A particular interest to atmospheric science is the effects of impurities on molecular transport and phase transition at grain boundaries in polycrystalline ice. Effects of doped HCl and SO2 on transport and phase transition at grain boundary of 2-4 micrometer polycrystalline ice were studied using a novel technique - Fast Thermal Desorption Spectroscopy (FTDS) [1] in the temperature range from -2 to -20 deg. C. In these experiments, H2O/D2O/H2O sandwich-like polycrystalline ice films doped with HCl and SO2 were vapor- deposited on the surface of a thin filament positioned in a vacuum chamber and maintained initially at cryogenic temperatures. After the deposition, the temperature of the filament was rapidly raised to a value near ice melting point, thus, initiating rapids H/D exchange reaction at the interface of H2O and D2O layers. Diffusion controlled rate of isotopic exchange in the desorbing film was monitored with a sensitive mass-spectrometer making it possible to gain quantitative information of the extent of diffusion of chemical species along the grain boundaries in polycrystalline ice samples. Comparisons of the experimental results in pure and doped polycrystalline ice show that water self diffusivity at the grain boundaries is significantly enhanced (by at least an order of magnitude) in the presence of HCl or SO2. The strong, non- Arrhenius, dependence of the water self-diffusivity on temperature indicates that this is due to grain boundary premelting [2], which may occur at temperatures as low as 10 deg. below ice melting point. We will discuss implication of this and other results of our FTDS experiments to various environmental phenomena. References: 1. Haiping Lu, Stephanie A. McCartney, M. Chonde, D. Smyla, and Vlad Sadtchenko, Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline ice films, J. Chem. Phys., 125, 044709, 2006. 2. Dash, J.G., A.W. Rempel and J.S. Wettlaufer, The physics of premelted ice and its geophysical consequences, Rev. Mod. Phys., 78, 695, 2006.
UR: http://home.gwu.edu/~vlad/
DE: 0740 Snowmelt
DE: 0754 Leads (4540)
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
DE: 4540 Ice mechanics and air/sea/ice exchange processes (0700, 0750, 0752, 0754)
DE: 4932 Ice cores (0724)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting