Environmental Engineering Reference
In-Depth Information
towardsmid-andhighlatitudes.Therefore,thenormalsituationisforlowerlevelsofozone
over the tropics and higher levels over the poles.
We will look at the biological effects of UV-B exposure later. For the moment, we
will just remember that life is no stranger to UV-B radiation and has evolved protective
mechanisms to deal with its impacts. However, the effectiveness of this protection depends
on UV-B irradiance being roughly within the limits that have existed during which life has
evolved these mechanisms.
It is time for another little digression. Sometimes, people become confused because
of an apparent contradiction. They read in the newspaper that high levels of ozone in the
air are a major contributor to poor summer air quality, but on the next page, they read that
scientists are worried about ozone depletion. The answer is quite simple. The ozone that is
responsible for protecting us from UV radiation is in the upper atmosphere (stratosphere).
The “excessive” ozone implicated in poor air quality is in the lower atmosphere (tropo-
sphere). Here, it is formed when hydrocarbons and nitrogen oxides (derived, for example,
from automobile exhaust and other fossil fuel combustion sources) interact with sunlight.
Ozone is a highly reactive molecule that injures biological tissues (plant and animal) - in
particular, the respiratory tract of people. It is also damaging to such manufactured materi-
als as rubber and nylon.
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