Modeling Studies of the Fate of Nonpolar Organic Chemicals
during Snowfall and Snowpack Metamorphosis
Frank Wania1, Ray G. Semkin2, John T. Hoff3, and D. Mackay4
Recent advances in the understanding of the interactions between nonpolar organic chemicals and
frozen water have revealed the immense importance of the iceair interface and the possibility of
quantitatively treating the adsorption process on the ice surface in terms of chemical-specific inter-
facial partition coefficients and the snow-specific surface area. As a result, it is now feasible to be
quantitative about many of the snow- and ice-related processes experienced by nonpolar organic
chemicals in cold environments. A series of simple fugacity-based chemical fate calculations that
aim to describe quantitatively nonpolar organic chemical behavior during snow scavenging, and
snowpack settling and melting, will be presented.
These model calculations are evaluated and calibrated as part of the Canadian Federal Govern-
ment's Northern Contaminants Program using available field data on snowpack, firn, and meltwater
concentrations and snow scavenging efficiencies of organic contaminants such as organochlorine
pesticides (OCPs), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons
(PAHs) measured in the environment, primarily in the Canadian Arctic. Specifically, the following
field measurements were sought to be reproduced in model simulations: 1) the change of concen-
trations of several PCBs and OCPs in a shallow Arctic snowpack during a one-month period prior to
melting, 2) the change of runoff concentrations of PCBs and OCPs in a small Arctic creek during a
one-month melting period, and 3) snow scavenging ratios of PCBs and PAHs measured during
several snowfall events in mid-latitudes.
The model calculations indicate that the specific surface area of ice crystals and the airice partition
coefficient of these chemicals are the two key parameters governing these processes, and it is the
uncertainty in these parameters that presently limits the capabilities of the models to simulate and
ultimately predict the effect of snow and ice on the behavior of nonpolar organic chemicals. Recent
advances in developing methods for measuring surface area make it possible to better characterize
the sorptive capacities of various types of snow and ice. If progress can also be made in measuring
reliably the partitioning coefficients of less volatile, nonpolar organic chemicals onto the ice sur-
face, a more rigorous evaluation of chemical snowpack models will become feasible.
1
WECC Wania Environmental Chemists Corporation, 280 Simcoe Street, Suite 404, Toronto, Ontario M5T
2Y5, Canada
2 Environment Canada, NWRI, 867 Lakeshore Road, Burlington, Ontario L7R 4A6, Canada
3 Department of Earth Science, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
4 Environmental and Resource Studies, Trent University, Peterborough, Ontario K9L 1N6, Canada
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