CFCs are fairly large, stable molecules consisting of chlorine, fluorine, and carbon. Since they are non-reactive in the troposphere, they found wide usage as an inert gas or a non-corrosive refrigerant (in the '40's, when CFCs were just starting to be used as a refrigerant, ammonia was commonly used...this gas was very corrosive to refrigeration plumbing and the fumes were dangerous).

It takes 1-2 years for an inert gas to thoroughly mix throughout the troposphere. Once that occurs, a gas can slowly diffuse upward through the stratosphere (the stratosphere is a global-scale inversion layer, so vertical convection cannot mix gases upward). The slow diffusion takes another 10-50 years before the CFC molecules reach the ozone layer. According to this time scale, we should just now be seeing some of the effects of CFCs on the stratospheric ozone.