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The Atmosphere

The Ozone Layer.

What is Ozone?

Oxygen decomposes high up in the atmosphere
in the presence of strong ultraviolet light from the sun,
leading to reactions with more oxygen molecules,
which produce ozone  - O₃.
oxygen                                   ozone 
3O_2(g)  +  ultraviolet light        2O_3(g)

What is the Ozone Layer?

Ozone high up in the atmosphere then acts to
absorb (soak up) ultraviolet light and prevent it reaching
the planet's surface. This is the so-called 'ozone layer'.

The ozone layer is essential for
complex living organisms (like you and me) to exist.
Without the ozone layer, all but very simple life forms
would be destroyed by the action of ultraviolet light.

Some chemicals, particularly CFCs,
destroy ozone in the upper atmosphere.
A CFC is a chlorofluorocarbon molecule.
It is similar to an alkane with all the hydrogen atoms
replaced with chlorine and fluorine atoms.

In the presence of ultraviolet light a CFC molecule will
decompose producing highly reactive chlorine free radicals.
These chlorine free radicals will react with ozone molecules
and turn them back into oxygen molecules.

When this happens on a large scale, a great deal of ozone is lost
and a so called "hole" in the ozone layer appears.
The hole allows more ultraviolet light to reach the surface
of the Earth which leads to a higher risk of sunburn,
faster ageing of the skin and a greater number of skin cancers.

CFCs have been widely used as refrigerants (in fridges)
and aerosol repellents in deodorants and perfumes.
The use of CFCs has been severely restricted in many countries
because of their damaging effect on the ozone layer.

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