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  • Some time ago the formation of polar stratospheric clouds was reported over Antarctica. Why were these formed? What happens when such clouds break up by the warmth of sunlight?

Some time ago the formation of polar stratospheric clouds was reported over Antarctica. Why were these formed? What happens when such clouds break up by the warmth of sunlight?

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Some time ago the scientists working in Antarctica reported depletion of the ozone layer, or it can also be said that the presence of an ozone hole was reported over the South Pole on Antarctic region.

It was found that a unique set of conditions was responsible for this ozone hole based on the seasons, viz.,

In summer: NO2 reacts with CH4 to form chlorine monoxide and chlorine atoms forming chlorine sinks, which prevents much ozone depletion.

In winter: Polar stratospheric clouds are formed over Antarctica that provides a surface on which chlorine nitrate formed gets hydrolysed and forms hypochlorous acid. It also reacts with HCl and produces molecular chlorine.

ClO + NO_{2} (g) \rightarrow ClONO_{2}

Cl (g) + CH_{4}\rightarrow CH_{3}(g) + HCl (g)

ClONO_{2} (g) +H_{2}O \rightarrow HOCl (g) + HNO_{3}

ClONO_{2} (g) + HCl \rightarrow Cl_{2} (g) + HNO_{3} (g)

                                                                                                 

When the sunlight returns there in spring, the warmth of the sun breaks the cloud and protolyzes HOCl and Cl_{2},

HOCl(g)\overset{h\nu }{\rightarrow}\dot{O}H(g)\dot{C}l(g) 

Cl_{2}\overset{h\nu }{\rightarrow}2\dot{C}l(g)

Therefore, the chain reaction of ozone depletion initiates with the formation of chlorine radicals.

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