Environmental Engineering Reference
In-Depth Information
7 Stratospheric Ozone Depletion
By three methods we may learn wisdom: First by reflection, which is noblest;
Second by imitation, which is easiest;
And third by experience, which is bitterest.
Confucius,
The Analects
When scientists in North America, Europe and the Soviet Union were beginning to detect
and understand the causes of freshwater and terrestrial acidification, another potentially
more serious problem (especially for the Arctic) was slowly being recognized: The strato-
spheric ozone layer that protects us all from the harmful effects of solar ultraviolet light was
thinning.
Before we go further into this part of the Arctic Messenger's story, we need a basic un-
derstanding of the behaviour and nature of oxygen and ozone in the stratosphere. Oxygen
can exist in three forms. Most commonly, it occurs as a molecule made up of two oxygen
atoms (O
2
). However, it can also occur alone as a single atom (atomic oxygen) or as a
molecule of three oxygen atoms (O
3
). This is ozone. In the stratosphere, highly energetic
shortwave ultraviolet radiation from the sun can break O
2
molecules apart into lone oxygen
atoms. When one of these free oxygen atoms bumps into an intact O
2
molecule, it can join
up with the molecule to form ozone. However, a cascade of chemical and physical processes
involving solar radiation and a number of naturally occurring compounds containing nitro-
gen, hydrogen and chlorine also continually break down stratospheric ozone. Therefore, the
amount of stratospheric ozone present at any moment in time is the result of a dynamic pro-
cess of production and removal.
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