The kinetics of the ozonation reaction of
1,1-diphenylethylene (DPE) on the surface of
ice grains (also called "artificial snow"), produced by
shock-freezing of DPE aqueous solutions or DPE vapor-deposition on pure
ice grains, was studied in the temperature range of 268 to 188 K. A remarkable and unexpected increase in the apparent ozonation rates with decreasing temperature was evaluated using the Langmuir-Hinshelwood and Eley-Rideal kinetic models, and by estimating the apparent specific surface area of the
ice grains. We suggest that an increase of the number of surface reactive sites, and possibly higher
ozone uptake coefficients are responsible for the apparent rate acceleration of DPE ozonation at the air-
ice interface at lower temperatures. The increasing number of reactive sites is probably related to the fact that organic molecules are displaced more to the top of a disordered interface (or quasi-liquid) layer on the
ice surface, which makes them more accessible to the gas-phase reactants. The effect of NaCl as a cocontaminant on ozonation rates was also investigated. The environmental implications of this phenomenon for natural
ice/snow are discussed. DPE was selected as an example of environmentally relevant species which can react with
ozone. For typical atmospheric
ozone concentrations in polar areas (20 ppbv), we estimated that its half-life on the
ice surface would decrease from ∼5 days at 258 K to ∼13 h at 188 K at submonolayer DPE loadings.