(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. $\mathrm{CF}_2\mathrm{Cl}_{2(g)}$ $\xrightarrow{UV}$ $\mathrm{Cl}_{(g)}^{\cdot}+\overset{.}{\mathrm{C}}\mathrm{F}_2\mathrm{Cl}_{(g)}$ (iii) These radicals further react with ozone and bring about its depletion. $\mathrm{Cl}_{(g)}^{\cdot}+\mathrm{O}_{3(g)}$ → $\mathrm{ClO}_{(g)}^{\cdot}+\mathrm{O}_{2(g)}$ $\mathrm{O}_{3(g)}$ $\overset{\text{UV}}{\rightleftharpoons}$ $\mathrm{O}_{2(g)}+\mathrm{O}_{(g)}$ $\mathrm{ClO}_{(g)}^{\cdot}+\mathrm{O}_{(g)}$ → $\mathrm{Cl}_{(g)}^{\cdot}+\mathrm{O}_{2(g)}$ (iv) Such regeneration of $\overset{.}{\mathrm{Cl}}$ radicals, causes continuous eating away of the $\mathrm{O}_3$ layer creating ozone holes.