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

include: a marine/maritime location; calm weather, low wind speeds, and non-turbulent airflow;
the existence of a temperature inversion; sunlight; and sub-zero temperatures (9). These
conditions are also favourable to the photochemically initiated heterogeneous production of
halogen atoms (Br and Cl) and halogen oxide radicals (BrO and ClO), which are assumed to be
involved in the mercury oxidative mechanism (9,10,11). BrO is produced in large quantities (> 20
pptv) after polar sunrise in the marine boundary layer, through the so-called “bromine explosion”
(4, 12, 13). Gas-phase HOBr reacts with a Br - ion in the saline sea ice surface to yield Br2, which
is then photolysed. The resulting Br atoms react with O3 to form BrO, which in turn react with
HO2 radicals to regenerate two HOBr, and the cycle repeats.
Several mechanisms have been proposed to explain the oxidation of gaseous elemental
mercury to RGM (10,11). These include the reactions between Hg 0 and halogen oxides or
halogen atoms to produce HgO, HgBr2 and HgCl2:
Br (Cl) + O3 → ClO (BrO) + O2 (1)
BrO (ClO) + Hg → HgO + Br (Cl) (2)
Hg + Br (Cl) → HgBr (HgCl) →→ HgBr2 (HgCl2) (3)
and the possible role of oxidants such as OH, HO2, O( 1 D and 3 P), and NO3 that are associated with
high levels of NO resulting from photodenitrification processes in the snowpack (14). A recent
review of the atmospheric chemistry of mercury can be found in (15).
In this paper we will consider the following mechanism for producing HgBrY:
Hg + Br (+ M) → HgBr (M = third body) (4)
HgBr (+ M) → Hg + Br (-4)
HgBr + Y (+ M) → HgBrY (Y = Br, I, OH, O2 etc.) (5)
3