Why there is ozone depletion mainly over Antarctica ?

Explanation

In Antarctica, winter months receive on sunlight and thus the temperature is extremely low`(-85^@ C)` . It facilitates the formation of ice clouds which provide the catalytic surface on which the chlorine atoms react with ozone and degrade it . This happens with the return of sun to Antartica in springs (September and October). Thus, ozone hole appears over Antarctica. mostly during spring.
Refer to text on page no. 436.