Chlorofluorocarbon. An ozon-depleting substance/greenhouse gas created by humans and is not emitted from any natural sources. CFCs (also called freons) were used as propellents in spray cans and cooling units (e.g. refrigerators and air conditioning), and as solvents, prior to the 1970s, causing depletion of the Earth's ozon layer. CFCs are highly stable compounds, with recovery times measured in decades. Following the recognition of their ozon-depleting effect the manufacture of CFCs has been phased out under the Montreal Protocol. (see also HFC)