Geology Reference
In-Depth Information
Observations of stratospheric constituents from
ER2
aircraft
Chemically perturbed
region
H
2
O
3.5 ppmv
NO
y
10 ppbv
~0.75 ppbv
250 ppbv
N
2
O
CFC11
ClO
~5 pptv
BrO
60
°
S
65
°
S
70
°
S
Polewards
Figure 33 Schematic representations of the changes in the concentration of some strato-
spheric species on entering the chemically perturbed region of the Antarctic
vortex (after ref. 57)
PSCs are the release of active chlorine from its usual reservoirs and the
removal of NO
x
from the system by the production of HNO
3
.
When the sun rises in the spring it triggers the depletion chemistry.
Cl
2
þ
hn
Cl
þ
Cl
-
(2.105)
Cl
þ
O
3
ClO
þ
O
2
-
(2.92)
But there is one further unforeseen modification as the concentration of
oxygen atoms is too low first thing in spring to regenerate Cl via the
normal reaction (2.93), so there is instead a further low-temperature
reaction that regenerates the chlorine atoms
ClO
þ
ClO
þ
M
-
(ClO)
2
þ
M
(2.106)
(ClO)
2
þ
hn
-
Cl
þ
ClOO
(2.107)
ClOO
þ
M
-
Cl
þ
O
2
þ
M
(2.108)
that can re-enter the catalytic cycle and destroy large amounts of ozone.
The absence of
significant concentrations of NO
x
stops
rapid
