Environmental Engineering Reference
In-Depth Information
higher regions of the earth's atmosphere - more precisely, in the stratosphere at an
altitude of 15 to 50 km. The UV light of the sun has been converting air oxygen (O
2
)
into ozone (O
3
) there forever. The ozone layer absorbs most of the dangerous UV radia-
tion. Certain gases, such as chlorofl uorocarbons (CFC) - from old refrigerators, air
conditioners and aerosol cans - decompose the ozone in the stratosphere. This is why
the ozone content in the ozone layer has decreased rapidly in recent decades. A hole in
the ozone formed, mainly over Antarctica. An increased amount of UV light now reaches
earth and is contributing to an increase in skin cancer. International agreements have
limited the use of CFC. Its use has been forbidden in new plants in Germany since 1995.
In the meantime a slow recovery has been observed in the ozone layer.
Yet the ozone in the ozone layer is itself a cause of the natural greenhouse effect.
For that reason the destruction of the ozone has actually produced a light cooling
effect.
'Bad ozone' close to earth, on the other hand, occurs as a reaction to nitrogen oxides,
oxygen and sunlight and causes the notorious summer smog. Ozone acts as an irritant
and in large concentrations is very toxic. In the natural ozone layer above an altitude of
15km this is not a problem, but it is a problem in the troposphere close to earth.
Furthermore, the tropospheric ozone close to earth also contributes to the greenhouse
effect. Unlike what happens in the ozone layer, the ozone concentration close to
earth is increasing. To this extent the ozone close to earth is what is warming up
the earth.
CFC was used as a coolant in air-conditioning systems and refrigerators. This not
only contributed to the greenhouse effect but also damaged the ozone layer. As
a result, the Montreal Protocol stipulated an end to CFC production worldwide,
allowing long periods of transition. HFCs are often used today as a CFC substitute.
These substances no longer use chlorine as an ingredient. Although this means
that they can no longer damage the ozone layer, HFC is still a problem for the
greenhouse effect. The HFC cooling agent R404A has a specifi c greenhouse poten-
tial of 3260. Therefore, 1kg of R404A is just as harmful as 3.26 tons of carbon
dioxide. But there are substitute substances available that are not damaging to
the climate. Unfortunately, these are currently only being used in a limited number
of areas.
Scientists have now developed a relatively good understanding of the different
effects of individual greenhouse gases and other factors on the earth's warming.
The greenhouse gases that result from the activities of people increase the refl ection
in the atmosphere and thus cause an increase in global warming. Figure 2.9 shows
the contribution of the different gases. The rise in solar activity is also causing a
slight increase in radiation. As described earlier, aerosols released through the
activities of people and the resulting cloud formations provide a cooling effect. Even
the ozone layer and changes in land use are producing a light cooling. If one jux-
taposes the cooling and the warming effects, it is the warming that predominates.
An increase in greenhouse gases and a decrease in aerosols through further improve-
ments in air purifi cation could even cause a considerable increase in warming over
the next few years.
