In summer season, chlorine atoms forming chlorine sinks, preventing much ozone depletion, whereas In winter, special type of clouds called polar stratospheric clouds are formed over Antarctica.

$\stackrel{•}{\mathrm{C}}\mathrm{l}\left(\mathrm{g}\right)+{\mathrm{CH}}_4\left(\mathrm{g}\right)\to \stackrel{•}{\mathrm{C}}{\mathrm{H}}_3\left(\mathrm{g}\right)+\mathrm{HCl}\left(\mathrm{g}\right)$