Environmental Engineering Reference
In-Depth Information
Table 2.2
Characteristics of the most important greenhouse gases.
(Status 2008)
Carbon
dioxide
Methane
HFC
Ozone
close to
earth
Laughing
gas (nitrous
oxide)
Chemical notation
CO
2
CH
4
diverse
O
3
N
2
O
Concentration in the atmosphere in ppm
385
1.77
<
0.01
0.034
0.32
Concentration in the year 1750
280
0.75
0
0.025
0.270
Annual increase in concentration
+ 0.4%
+0.4%
Varies
+0.5%
+0.25%
Greenhouse potential compared to CO
2
1
23
>
1000
>
1000
296
Duration in the atmosphere in years
5-200
12
Varies
<
0.1
114
Refl ection in W/m
2
1.66
0.5
0.35
0.35
0.16
Percentage of anthropogenic
greenhouse effect
56%
16%
11%
12%
5%
Interestingly, agriculture releases the largest proportion of methane. Livestock
rearing, decaying biomass and rice cultivation are the farming activities that produce
the most methane. Unlike carbon dioxide, it is not integrated into a biological cycle.
When ruminants digest green fodder, they create methane which they belch into the
atmosphere. A single cow or a herd would not pose a problem for the climate, but
the number of cattle worldwide is now so large that they represent a real threat to
the environment. Meat consumption per head has increased dramatically during the
past few decades, as has the number of people, so that there are now more than 1.3
billion cattle on earth.
Other greenhouse gases such as nitrous oxide (laughing gas) are created through
farming due to an excessive use of nitrogeneous fertilisers. Overall, agriculture
contributes around 15% of the greenhouse effect caused by man.
Other key greenhouse gases include ozone, fl uoride hydrocarbons (HFC and halons),
steam and sulphur hexafl uoride (SF
6
). Air pollutants help to create low-level ozone.
These pollutants originate in part from motorized traffi c and, therefore, as a result
of the burning of fossil fuels. The ozone problem has become a familiar one because
of the health risk associated with summer smog. However, what is less known is
the impact of the ozone on the greenhouse effect. SF
6
is used in the electricity sector
but the amount causing a greenhouse effect is relatively minimal.
Will the Hole in the Ozone Layer Keep Making Earth Warmer?
The ozone hole and the greenhouse effect are both global environmental
threats. Yet they have very little relationship to one another.
With the ozone a distinction must be made between the ozone layer at high altitudes and
ozone at a low level. The natural ozone layer with the 'good ozone' is located in the
