FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

Fate of Mercury in the Arctic 98
and thus the resulting rate constants for the reactions can be estimated to be in the order of 6x10 -14
cm 3 molec -1 sec -1 .
Skov et al., 2003, Appendix C, analysed the data using a relative rate study, and found direct
evidence in a strong linear correlation (>99.9% significance) that ozone and GEM have a mutual
dependence that cannot be explained solely by meteorology.
Goodsite et al., 2003, Appendix C, propose a plausible mechanism for the oxidation of gaseous
Hg (0) to the divalent gaseous form. The mechanism is modeled from the limited data known of Br
and Hg reactions in the Arctic, given the data from Station Nord, with a predicted lifetime of Hg to
be approximately 10 hours during AMDEs.
The mechanism is consistent with the kinetics, thermodynamics and field observations, but the
final end product is still not definitively known, due to the measurement method in the field, i.e.,
reactive gaseous mercury is operationally determined and defined.
The hypothesized mechanism is not the same as the mechanisms otherwise derived (e.g.
Lindberg et al., 2002, Appendix C), where the depletion of atmospheric boundary-layer mercury is
said to be due to a reaction between gaseous elemental mercury, GEM, and BrO free radicals or
mechanisms resulting in the product HgCl2.
The proposed reaction mechanism is that gaseous elemental mercury, Hg (0) combines with Br
atoms, called X, coming from the polar sunrise destruction of ozone, in a reversible reaction,
forming the energised HgBr*.
Through a third body reaction, M, where M is N2 or O2, the HgBr radical is formed.
The HgBr radical can live long enough at the low temperatures of the Arctic to combine with
O2 forming the HgBrOO peroxy radical or can combine with Br forming HgBr2.
It is not likely to react with Cl, since this reaction would be endothermic.