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

Fate of Mercury in the Arctic 97
That ozone and GEM are directly dependent on one another, or on a mutual factor, can be seen
in Figure 12., page 70, where R 2 = 0.8 this is comparable with what is found at the other Arctic
stations. given the strong correlation between ozone and GEM, observed at Station Nord during
AMDE’s. A direct reaction between ozone and GEM can be excluded due to the approximately 1
year lifetime of GEM with respect to the present ozone concentrations (Lin and Pekonen 1999).
However, a speculatively plausible reaction mechanism can be reasoned from what is presently
known.
A plausible mechanism for the oxidation of elemental mercury to divalent gaseous mercury
after polar sunrise in the Arctic
Bottenheim (personal communication) showed that Bromine builds up due to the “bromine
explosion” mechanism ((3) – (6)):
O Br ⎯⎯→O
+ BrO
3 + 2
(3)
BrO +
+ BrO ⎯⎯→
2Br O2
(4)
BrO + HO2
⎯⎯→
HOBr
(5)
−
Br + HOBr ⎯⎯→
2Br
therefore either Br or BrO is a candidate for GEM removal is. An analogue mechanism may occur
with Cl, however Cl and ClO cannot initially be ruled out, as significant Cl removal of organic
compounds have been observed during AMDE (e.g. Boudries and Bottenheim, 2000). Taking
thermodynamics into consideration however, shows that the reaction: Hg (O) with Cl and radical
ClO are less likely to occur than with Br and radical BrO.
The lifetime of GEM is observed to be typically about 10 hours during AMDE as confirmed
also by this data from Station Nord. Hausmann and Platt observed up to 20 pptv of ClO and BrO
(6)