Here's why:

* Naturally occurring: CFCs do not exist naturally in the atmosphere. They are entirely man-made compounds.

* Industrial applications: CFCs were primarily used as refrigerants, propellants in aerosol sprays, and solvents.

* Global ban: Due to their severe impact on the ozone layer, production and use of CFCs have been largely banned globally through the Montreal Protocol.

While other gases like methane and carbon dioxide have both natural and anthropogenic sources, CFCs are unique in being entirely produced by human activity.