Answer:
In Antarctica, the
climatic conditions are quite different. In winters, there are special types of
clouds called Polar stratospheric clouds. No ozone is generated during the long
dark Antarctic winter. Meanwhile a heterogeneous reaction occurring on clouds
of ice crystals at -\[85{}^\circ C\]produces species such as \[C{{l}_{2}}\]and\[HOCl\].
\[ClO+N{{O}_{2}}\to
ClON{{O}_{2}}\]
\[Cl+C{{H}_{4}}\to
\overset{\centerdot }{\mathop{C}}\,{{H}_{3}}+HCl\]
\[ClON{{O}_{2}}+{{H}_{2}}O\to
HOCl+HN{{O}_{3}}\]
\[ClON{{O}_{2}}+HCl\to
C{{l}_{2}}+HN{{O}_{3}}\]
When the sun reappears in
September, these molecules decompose photo chemically to form Cl atoms.
\[HOCl\xrightarrow{hv}{}^{\bullet
}OH+C{{l}^{\bullet }}\]
\[C{{l}_{2}}\xrightarrow{hv}2C{{l}^{\bullet
}}\]
The reactive chlorine atoms are
thus rendered free to deplete ozone.
Due to polar stratospheric
clouds, a tight whirlpool of wind is formed in the stratosphere which surrounds
Antarctica. It is called polar vortex. It is so rigid that it cuts-off
Antarctica from the surrounding ozone rich air of the non-polar regions. As a
result, the ozone hole remains unfilled. After the spring, when the intensity
of sunlight increases and the vortex breaks down. The ozone rich air from
surroundings immediately rushes to fill up the ozone hole.
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