posted on 2016-02-19, 04:40authored byDebajyoti Ray, Joseph
K’Ekuboni Malongwe, Petr Klán
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.