Geology Reference
In-Depth Information
the boundary layer and the free troposphere and sunlight to drive the
required photolysis of gaseous bromine (see reaction (2.75)) released
heterogeneously through chemical processes on the ice. Because of the
prerequisites for strong surface inversions to confine the air and
sunlight, episodes of bromine explosion events and boundary layer
ozone depletion tend to be confined to spring. It is thought that frost
flowers in the Antarctic, which are formed on a liquid layer with high
salinity on top of the sea ice surface, are likely to provide a large
surface area for the heterogeneous release of reactive bromine but the
evidence is not unequivocal.
With respect to iodine chemistry, the major sources of iodine are
thought to be from macroalgal sources releasing organoiodine com-
pounds.
46
Photolysis of the organoiodine compounds releases the iodine.
RI
x
þ
hn
-
R
þ
I
(2.79)
I
þ
O
3
-
IO
þ
O
2
(2.80)
During daylight hours iodine monoxide, IO exists in a fast photochem-
ical equilibrium with I, viz.
IO
þ
hn
-
I
þ
O
(2.81)
The Bromine explosion
Sea ice surface
Aerosol
+HO
2
BrO
+O
3
+BrO
HOBr
HOBr
+Br
-
Br
Br
2
HOBr
Heterogeneous release of bromine
on sea salt surfaces
BrO
+
HO
→
HOBr
+
O
2
2
−
+
HOBr
(
g
)
+
Br
(
aq
)
+
H
→
Br
(
g
)
+
H
O
2
2
Br
,
BrO
2
O
→
3
O
Catalytical ozone destruction
3
2
Figure 21 A schematic representation of the so-called Bromine explosion mechanism
where effectively one BrO molecule is converted to two by oxidation of
bromide from a suitable aerosol surface
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