Geology Reference
In-Depth Information
and
OH
þ
CH
4
-
CH
3
þ
H
2
O
(2.13)
CH
3
þ
O
2
þ
M
-
CH
3
O
2
þ
M
(2.14)
In low-NO
x
conditions, HO
2
can react with ozone leading to further
destruction of ozone in a chain sequence involving production of
hydroxyl radicals.
HO
2
þ
O
3
-
OH
þ
2O
2
(2.15)
OH
þ
O
3
-
HO
2
þ
O
2
(2.16)
Alternatively, it can recombine to form hydrogen peroxide (H
2
O
2
)
HO
2
þ
HO
2
-
H
2
O
2
þ
O
2
(2.17)
or react with organic peroxy radicals such as CH
3
O
2
to form organic
hydroperoxides,
CH
3
O
2
þ
HO
2
-
CH
3
O
2
H
þ
O
2
(2.18)
The formation of peroxides is effectively a chain termination reaction, as
under most conditions these peroxides can act as effective sinks for HO
x
.
In more polluted conditions (high-NO
x
), peroxy radicals catalyse the
oxidation of NO to NO
2
HO
2
þ
NO
OH
þ
NO
2
-
(2.19)
leading to the production of ozone from the subsequent photolysis of
nitrogen dioxide and reaction of the photoproducts, i.e.
NO
þ
O(
3
P)
NO
2
þ
hn(l
o
420 nm)
-
(2.2)
O
þ
O
2
þ
M
-
O
3
þ
M
(2.20)
Hydroxyl radicals produced in reaction (2.19) can go on to form more
peroxy radicals (e.g. via reactions (2.11) and (2.13)). Similarly to HO
2
,
CH
3
O
2
can also oxidise NO to NO
2
.
CH
3
O
2
þ
NO
-
CH
3
O
þ
NO
2
(2.21)
