Environmental Engineering Reference
In-Depth Information
Table 8.4
Global warming potential, relative to carbon dioxide for different time horizons and atmospheric
lifetimes for selected gases.
Chemical species
Chemical
formula
Lifetime
(years)
Global warming potential
(time horizon)
20 years 100 years 500 years
Carbon dioxide
Methane
Nitrous oxide
CO
2
CH
4
N
2
O
Variable
12.0
114
1
62
275
1
23
296
1
7
156
Hydroflurocarbons
(HFCs)
HFC-23
CHF
3
260
9,400
12,000
10,000
HFC-32
CH
2
F
2
5.0
1,800
550
170
HFC-41
CH
3
F
2.6
330
97
30
HFC-125
C
2
HF
5
29
5,900
3,400
1,100
HFC-134
C
2
H
2
F
4
9.6
3,200
1,100
310
HFC-134a
CH
2
FCF
3
13.8
3,300
1,300
400
HFC-152
CH
2
FCH
2
F
0.5
140
43
13
HFC-152a
C
2
H
4
F
2
1.4
410
120
37
HFC-143
C
2
H
3
F
3
3.4
1,100
330
100
HFC-143a
C
2
H
3
F
3
52
5,500
4,300
1,600
HFC-227ea
C
3
HF
7
33.0
5,600
3,500
1,100
HFC-236fa
C
3
H
2
F
6
220
7,500
9,400
7,100
HFC-245ca
C
3
H
3
F
5
5.9
2,100
640
200
Perfluorocarbons
(PFCs)
Perfluoromethane
CF
4
50,000
3,900
5,700
8,900
Perfluoroethane
C
2
F
6
10,000
8,000
11,900
18,000
Perfluoropropane
C
3
F
8
2,600
5,900
8,600
12,400
Perfluorobutane
C
4
F
10
2,600
5,900
8,600
12,400
Perfluorocyclobutane
c-C
4
F
8
3,200
6,800
10,000
14,500
Perfluoropentane
C
5
F
12
4,100
6,000
8,900
13,200
Perfluorohexane
C
6
F
14
3,200
6,100
9,000
13,200
Sulphur
hexafluoride
SF
6
3,200
15,100
22,200
32,400
Adapted from Intergovernmental Panel on Climate Change (IPCC), 2001.
The global warming potential (GWP) of a GHG is a relative measure of its ability to act as
a GHG with respect to carbon dioxide (Table 8.4). For example, nitrous oxide has a 100-year
GWP of 296. This means that 1 tonne of nitrous oxide gas emitted into the atmosphere is the
same as the emission of 296 tonnes of carbon dioxide.
Emissions of GHGs are expressed in terms of “Teragrams of CO
2
Equivalents”:
Tg of CO Eq
=
(Mass of gas in Gg)
×
(GWP)
×
(1 Tg/1000 Gg)
2
Where,
Tg CO
2
Eq = Teragrams of CO
2
Equivalents
Gg = Gigagrams (equivalent to a thousand metric tons)
Tg = Teragrams
GWP = Global Warming Potential
1 Tg/1000 Gg = conversion factor (EPA, 2010b).
Ozone-depleting substances
Chlorine and bromine radicals coming from chlorinated and brominated hydrocarbons are
the main chemical species that catalyze the destruction of ozone in the stratosphere. Since
