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?
This is depletion of the ozone layer. In the summer season, the nitrogen dioxide and methane reacted with the chlorine monoxide and chlorine radicle respectively forming chlorine sinks thereby preventing the depletion of ozone.
ClO + NO2 (g) → ClONO2
Cl (g) + CH4→ CH3(g) + HCl (g)
ClONO2 (g) +H2O → HOCl (g) + HNO3
ClONO2 (g) + HCl → Cl2 (g) + HNO3 (g)
When the sunlight returned back in the spring it breaks up clouds and HOCl and molecular chlorine gets photolysed by sunlight to form chlorine radicles:
Cl2 (g) → 2 Cl
These chlorine radicles further caused the ozone depletion.