(i) The main reason for ozone layer depletion besides other gases are chlorofluorocarbons (CFCs).
(ii) Once CFCs are released into the atmosphere, they reach the stratosphere and release free-radicals by the action of sunlight.
CF2Cl2(g)

UV

→

.

Cl(g)

+

.

C

F2Cl(g)
(iii) These radicals further react with ozone and bring about its depletion.

.

Cl(g)

+O3(g) → Cl

.

O(g)

+O2(g)
O3(g)

UV

⇌

O2(g)+O(g)
Cl

.

O(g)

+O(g) →

.

Cl(g)

+O2(g)
(iv) Such regeneration of

.

Cl

radicals, causes continuous eating away of the O3 layer creating ozone holes.