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High above our heads in a
layer of the atmosphere known as the stratosphere is a small amount
of ozone gas. This gas is made up of molecules each containing three
atoms of oxygen; its chemical formula is 03.
(The formula of oxygen gas is 02.) The 'ozone
layer' absorbs harmful ultraviolet radiation from the sun.
Scientist measure ozone layer
thickness by measuring how much ultraviolet radiation reaches the ground,
using a Dobson ozone spectrophotometer. Ozone layer thickness is measured
in Dobson units. The higher the number the thicker the ozone layer.
Ozone is produced and destroyed
naturally. Since the 1970s, gases produced for commercial purposes have
been destroying the ozone layer, upsetting the natural equilibrium that
existed. It is planned that by 2005 in developed countries and 2015
in developing countries, the use of ozone depleting gases, such as CFCs,
will be phased out.
CFCs (chlorofluorocarbons)
are used in spray cans, in the plastics industry, as refrigerants and
for cleaning electronic circuit boards. Halons, used as fire extinguishing
chemicals, also destroy ozone.
See the following animated
model to understand how ozone is destroyed by CFCs.
A damaged ozone layer means
that more of the sun's harmful UV radiation is able to reach the earth's
surface. This radiation can cause sunburn, skin cancer and eye diseases.
Go to the following link for more
information about UV radiation.
Ozone depletion occurs over much of the planet. The depletion over Antarctica
(the Antarctic ozone hole) peaks in spring, when sunlight activates
chemical reactions in which chlorine released from the CFCs rapidly
destroys ozone molecules. These reactions happen on ice crystals in
the very cold, high-altitude clouds above Antarctica.
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