Geology Reference
In-Depth Information
Primary Sources of Chlorine and Bromine for
the Stratosphere in 1999
Chlorine source gases
Other gases
Methyl chloroform (CH
3
OCl
3
)
HCFC
3
(e.g. HCFC22-CHCIF
2
)
CFC-113 (CCl
2
FCCF
2
)
1%
4%
5%
7%
3000
Carbon tetrachloride (CCl
4
)
12%
CFC-11 (CCl
3
-F)
2000
23%
CFC-12 (CCl
2
F
2
)
32%
1000
Methyl chloride (CH
3
Cl)
Natural
Sources
16%
0
Figure 26 Stratospheric source gases - A variety of gases transport chlorine into the
stratosphere. These gases are emitted from natural sources and human activ-
ities. For chlorine, human activities account for most that reaches the strat-
osphere. The CFCs are the most abundant of the chlorine-containing gases
released in human activities. Methyl chloride is the most important natural
source of chlorine
58
ozone. For two reasons it became apparent that this would not be the
case. First, the number of aeroplanes required to observe a loss of ozone
would be 1500, flying 7 h a day, 7 days a week. This number of
aeroplanes would be able to transport the population of London to
New York, or vice versa in a matter of weeks. Second, refinements to the
understanding of the fundamental chemistry used to make the initial
predictions have shown the impact is likely to be less. A warning note
should be interposed at this point because the rise in international air
travel and the new generation of aircraft means that this problem is back
on the scientific agenda.
53,54
The potential of subsonic aircraft to pollute
the upper atmosphere is now being studied extensively. Other areas of
potential stratospheric pollution have been identified such as NASA
space shuttle launches and the extensive use of agricultural fertilisers.
