Environmentally Relevant Organic Compounds at the Air-Ice Interface


                                 Debajyoti Ray^1 and Petr Klán^1,2

^1Research Centre for Toxic Compounds in the Environment, Faculty of Science, Masaryk University,
Kamenice 3, 62500 Brno, Czech Republic

^2Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5, 62500, Brno, Czech
Republic


The compartments of the Earth’s system are firmly interconnected. Alteration in one component can
produce strong impact on the state of other compartments. Therefore, the physical and chemical
processes undergoing in the cryosphere have a strong impact on the biogeochemical cycles and fates
of the organic contaminants in the global scale. The chemical processes are significant in terms of
removal of the contaminants or often generation of reaction products which are more toxic and more
bioaccumulative than the original contaminants. Hence worldwide current research on snow chemistry
is aimed to a better understanding about the location of contaminants in snow/ice, the reaction
mechanism followed and the effects of environmental parameters, such as temperature, on the
chemical processes.

We investigated the applicability of artificial snow as an alternative of natural snow to be
utilized in the laboratory. The apparent specific surface area was determined using valerophenone
photochemistry and ozonolysis of 1,1-diphenylethylene (DPE). The calculated specific surface area
of artificially produced snow grains (80–150 cm^2g^–1) and that of natural snow grains (125
cm^2g^–1) were comparable and in good agreement with the values determined by other physical
methods. The cage effect values were obtained to confirm that impurities, which are mostly ejected
to the surface of snow during the freezing of the aqueous solutions, form a two-dimensional layer
at the air-ice interface. We found that the heterogeneous reaction of ozone and snow-surface
adsorbed DPE follows a Langmuir-Hinshelwood type of reaction kinetics at 258K. Also the temperature
dependence of DPE ozonation was studied in the temperature range of 268 to 188K. 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 ice grains. We propose that an increase of the number of surface reactive sites and
possibly higher ozone uptake coefficients are responsible for apparent rate acceleration of DPE
ozonation at the air–ice interface at lower temperatures. Our results can be beneficial for
understanding heterogeneous reactivity of volatile and semi-volatile organic compounds on the
natural ice surface.


Keywords: artificial snow, photochemistry, cage effect, ozonolysis, specific surface area,
Langmuir-Hinshelwood kinetics and Eley-Rideal kinetics.

References:

1. Kurkova, R.; Ray, D.; Nachtigallova, D.; Klan, P. Chemistry of small organic molecules on snow
grains: The applicability of artificial snow for environmental studies. Environ. Sci. Technol.
2011, 45, 3430−3436.

2. Ray, D.; Kurkova, R.; Hovorkova, I.; Klan, P. Determination of the specific surface area of snow
using ozonation of 1,1-diphenylethylene. Environ. Sci. Technol. 2011, 45, 10061−10067.

3. Ray, D.; Malongwe, J.; Klan, P. Rate Acceleration of the Heterogeneous Reaction of Ozone with a
Model Alkene at the Air−Ice Interface at Low Temperatures. Environ. Sci. Technol., 2013, DOI:
10.1021/es304812t.