Scientists noticed that the ozone layer was thinning. what was occurring at the same time?

At the same time there is increased usage of chlorofluorocarbon [CFC].
CFC are halogenated compounds which have ability to destroy the ozone layer. When ultraviolet ray strike CFC in the atmosphere, it breaks the forces holding the molecule together and yield a chlorine atom. The chlorine atom then react with the ozone layer, breaking it apart and destroying it.

Deposition is the transition of matter going from gas to solid without passing through the liquid phase.a.) gas—-> solid