Environmental Engineering Reference
In-Depth Information
Table 1
Atmospheric lifetime and GWPs relative to CO
2
at different time horizon for various
green house gases
Atmospheric gases
Global warming potentials (GWPs)
Lifetime
(yrs)
(Time horizon in years)
20 yrs
100 yrs
500 yrs
~5-200
b
Carbon dioxide (CO
2
)
1
1
1
Methane
a
(CH
4
)
12
c
62
23
7
114
c
Nitrous oxide (N
2
O)
275
296
156
Hydrofluorocarbons
HFC-23 (CHF
3
)
9400
12000
10000
260
HFC-32 (CH
2
F
2
)
1800
550
170
5.0
HFC-41 (CH
3
F)
330
97
30
2.6
HFC-125 (CHF
2
CF
3
)
5900
3400
1100
29
HFC-134 (CHF
2
CHF
2
)
3200
1100
330
9.6
HFC-134a (CH
2
FCF
3
)
3300
1300
400
13.8
HFC-143 (CHF
2
CH
2
F)
1100
330
100
3.4
HFC-143a (CF
3
CH
3
)
5500
4300
1600
52
HFC-152 (CH
3
CHF
2
)
140
43
13
0.5
HFC-152a (CH
3
CHF
2
)
410
120
37
1.4
HFC-161 (CH
3
CH
2
F)
40
12
4
0.3
Fully fluorinated gases
SF
6
15100
22200
32400
3200
CF
4
3900
5700
8900
50000
C
2
F
6
8000
11900
18000
10000
GWPs are an index for estimating relative global warming contribution due to atmospheric emis-
sion of a kg of a particular greenhouse gas compared to emission of a kg of carbon dioxide.
Data
source
IPCC (
2001
)
a
The methane GWPs include an indirect contribution from stratospheric H
2
O and O
3
production
b
No single lifetime can be defined for CO
2
because of the different rates of uptake by different
removal processes
c
The values for methane and nitrous oxide are adjustment times, which incorporate the indirect
effects of emission of each gas on its own lifetime
under the regulations of the Montreal Protocol and its Amendments (IPCC
2001
).
The halocarbon substitute compounds (e.g. CHF
2
Cl and CF
3
CH
2
F) and some
other synthetic compounds such as perfluorocarbons and sulphur hexafluoride,
SF
6
, are also greenhouse gases. Their concentrations are currently increasing
(Table
1
) (IPCC
2001
).
Atmospheric sulfate aerosols have increased sharply during the past one-and-
a-half centuries or so, with an overall increase in sulfate emissions from 1 Mt S
in 1850 to 70 Mt S in the 1990s. Sulfate aerosols are mostly concentrated in the
Northern Hemisphere, with distinct concentration maxima near major polluted
regions (Lefohn et al.
1999
; Smith et al.
2001
). Carbon monoxide (CO) is identi-
fied as an important indirect greenhouse gas, which acts as a HO
•
sink (thereby
enhancing the lifetime of many direct greenhouse gases) and is involved in the for-
mation of tropospheric O
3
. A model study indicates that the emission of 100 Mt
