Answer:
Two types of
compounds, nitric oxide and chlorofluorocarbons (Freons) have been found to be most
responsible for depleting ozone layer and creating a hole into it (known as
ozone hole).
Nitric oxide reacts with ozone in stratosphere forming
oxygen and\[N{{O}_{2}}\].\[N{{O}_{2}}\]further reacts with free oxygen atoms
available in the stratosphere producing back NO.
\[NO+{{O}_{3}}\to {{O}_{2}}+N{{O}_{2}}\]
\[N{{O}_{2}}+O\to NO+{{O}_{2}}\]
Thus, NO is not consumed but depletion of ozone occurs.
CFC first undergo photochemical decomposition to give
chlorine atoms or free radicals.
\[C{{F}_{2}}C{{l}_{2}}\xrightarrow{hv}\overset{\centerdot
}{\mathop{C{{F}_{2}}}}\,Cl+\overset{\centerdot }{\mathop{Cl}}\,\]
\[CFC{{l}_{3}}\xrightarrow{hv}\overset{\centerdot
}{\mathop{CF}}\,C{{l}_{2}}+\overset{\centerdot }{\mathop{Cl}}\,\]
Chlorine atoms destroy the ozone layer through a sequence
of reactions which are repeated over and again.
\[\overset{\centerdot
}{\mathop{Cl}}\,+{{O}_{3}}\to {{O}_{2}}+Cl\overset{\centerdot }{\mathop{O}}\,\]
\[Cl\overset{\centerdot
}{\mathop{O}}\,+O\to \overset{\centerdot }{\mathop{Cl}}\,+{{O}_{2}}\]
Although above reactions take place in all parts of stratosphere,
yet ozone hole has mainly been observed in the stratosphere over Antarctica on
account of strange climatic conditions.
Consequences of depletion of ozone layer:
UV-radiation filter into troposphere. These lead to ageing
of skin, cataract, sunburn, skin cancer, killing of phytoplanktons, damage to
fish productivity, etc.
Plant proteins are easily affected by UV-radiations. It also
increases evaporation of surface water through stomata of leaves and decreases
the moisture content of soil. UV-radiations damage paints and fibres.
Ozone depletion has very strong effect on climate and ecology.
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