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Ozone (O3) occurs naturally
in the atmosphere. It forms a layer
which is denser towards the poles and
thinnest in the tropics (around the
equator). Ozone is formed in the
atmosphere when ultraviolet radiation
from the sun strikes the stratosphere
splitting oxygen molecules (O2)
into atomic oxygen (O). The atomic
oxygen quickly combines with further
molecules to form ozone.
O2 + hv → O +
O
(1)
O + O2 → O3
(2)
Ozone is a pollutant in the troposphere
because in the presence of sunlight it
breaks into O2 and O and
reacts with oxides of nitrogen and
hydrocarbon which result in smog whereas
in the stratosphere it absorbs the UV
radiation of sun and protects the living
organisms and hence a life saver in the
stratosphere.
Although the UV radiation splits the
ozone molecule, ozone can reform through
following reactions resulting in no net
loss of ozone
O3 + hv → O + O2
(3)
O + O2 → O3
(4)
Ozone is destroyed by the following
reaction with atomic oxygen
O + O3 → 2O2
(5)
The reactions 1-4 are known as the
“Chapman reactions” and the layer of
ozone formed in the stratosphere by
these reactions is known as “Chapman
Layer”.
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