Publication Date:
2021-03-29
Description:
Snow in the environment acts as a host to rich
chemistry and provides a matrix for physical exchange of
contaminants within the ecosystem. The goal of this review
is to summarise the current state of knowledge of physical
processes and chemical reactivity in surface snow with relevance
to polar regions. It focuses on a description of impurities
in distinct compartments present in surface snow, such
as snow crystals, grain boundaries, crystal surfaces, and liquid
parts. It emphasises the microscopic description of the
ice surface and its link with the environment. Distinct differences
between the disordered air–ice interface, often termed
quasi-liquid layer, and a liquid phase are highlighted. The reactivity
in these different compartments of surface snow is
discussed using many experimental studies, simulations, and
selected snow models from the molecular to the macro-scale.
Although new experimental techniques have extended our
knowledge of the surface properties of ice and their impact
on some single reactions and processes, others occurring on,
at or within snow grains remain unquantified. The presence
of liquid or liquid-like compartments either due to the formation
of brine or disorder at surfaces of snow crystals below
the freezing point may strongly modify reaction rates. Therefore,
future experiments should include a detailed characterisation
of the surface properties of the ice matrices. A further
point that remains largely unresolved is the distribution of
impurities between the different domains of the condensed
phase inside the snowpack, i.e. in the bulk solid, in liquid at
the surface or trapped in confined pockets within or between
grains, or at the surface. While surface-sensitive laboratory
techniques may in the future help to resolve this point for
equilibrium conditions, additional uncertainty for the environmental
snowpack may be caused by the highly dynamic
nature of the snowpack due to the fast metamorphism occurring
under certain environmental conditions.
Due to these gaps in knowledge the first snow chemistry
models have attempted to reproduce certain processes like
the long-term incorporation of volatile compounds in snow
and firn or the release of reactive species from the snowpack.
Although so far none of the models offers a coupled
approach of physical and chemical processes or a detailed
representation of the different compartments, they have successfully
been used to reproduce some field experiments. A
fully coupled snow chemistry and physics model remains to
be developed.
Keywords:
air, ice, liquids, quasi-liquids, solids; snow
;
551
Language:
English
Type:
article
,
publishedVersion
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