How the release of CFCs at the earth's surface damages the ozone layer ?

Question

and also why n-propyl bromide might be less of a threat?

Answer 1

CFC + sunlight ---> nascent chlorine

chlorine + ozone ---> chlorine dioxide

chlorine dioxide + sunlight ---> nascent chlorine

and obviously, you can guess what happens.

Answer 2

They are trying methods of refigeration and air conditioning to further negate any deleterious effects on the earth.