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The presence of snow greatly perturbs the
composition of near-surface polar air, and the higher concentrations of
hydroxylradicals (OH) observed result in a greater oxidative capacityof the lower atmosphere. Emissions of nitrogen oxides, nitrousacid,
light aldehydes, acetone, and molecular halogens have alsobeen
detected. Photolysis of nitrate ions contained in the snowappears to
play an important role in creating these perturbations.OH formed in
the snowpack can oxidize organic matter and halideions in the snow,
producing carbonyl compounds and halogens thatare released to the
atmosphere or incorporated into snow crystals.These reactions modify
the composition of the snow, of the interstitialair, and of the
overlying atmosphere. Reconstructing the compositionof past
atmospheres from ice-core analyses may therefore requirecomplex
corrections and modeling for reactive species.
1 CNRS, Laboratoire de Glaciologie et
Géophysique de l'Environnement, B.P. 96, 54 Rue Molière,
38402 Saint Martin d'Hères cedex, France.
2 Department of Chemistry and Department of Earth
and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907, USA.
*
To whom correspondence should be addressed. E-mail:
florent{at}lgge.obs.ujf-grenoble.fr, pshepson{at}purdue.edu
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