Geoscience Reference
In-Depth Information
CHLOROFLUOROCARBONS AND HALONS
Chlorofluorocarbons (CFCs) contain atoms of carbon, fluorine, and chlo-
rine. They are manufactured for use in spray cans, blowing foams and pack-
ing material, and as solvents and refrigerants. In their use as refrigerants they
are designed to absorb longwave radiation, so it is no surprise that they are
extremely strong greenhouse gases. CFCs are nonreactive in the troposphere,
which contributes to their long residence times, and when they migrate into
the stratosphere they are decomposed by ultraviolet light and contribute to the
destruction of stratospheric ozone.
The Montreal Protocol of 1987, strengthened by the London Agreement in
1990, established regulations to reduce CFC emissions to protect stratospheric
ozone. Substitutes for these ozone-destroying compounds have been devel-
oped, for example, HFCs (hydrofluorocarbons) and HCFCs (hydrochloroflu-
orocarbons). These compounds react with OH and, therefore, have shorter
atmospheric lifetimes and less migration into the stratosphere, but they are still
strong greenhouse gases. Figure 10.5 shows the trends in the concentrations of
selected CFCs and HCFCs in the troposphere.
(a)
(b)
265
102
100
260
98
255
96
250
94
92
245
Northern hemisphere
Global
Southern hemisphere
Northern hemisphere
Global
Southern hemisphere
90
240
88
235
86
1998
2000
2002
2004
2006
2008
2010
2012
1998
2000
2002
2004
2006
2008
2010
2012
Year
Year
(c)
(d)
240
22
Northern hemisphere
Global
Southern hemisphere
Northern hemisphere
Global
Southern hemisphere
230
20
220
210
18
16
200
180
160
14
12
10
8
140
120
1998
2000
2002
2004
2006
2008
2010
2012
1998
2000
2002
2004
2006
2008
2010
2012
Year
Year
Figure 10.5 Global concentrations of (a) CFC-11, (b) CCI 4 , (c) HCFC-22, and (d) HCFC-142b.
Data from NOAA/ESRL halocarbons program. Units are parts per trillion (ppt).
 
 
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