CFCs

CFCs, or chlorofluorocarbons, are a class of man-made halogenated hydrocarbons that contain chlorine and fluorine bonded to carbon. They are typically fully fluorinated or chlorinated, nonflammable, chemically stable, and have long atmospheric lifetimes. Common CFCs include CFC-11 (trichlorofluoromethane) and CFC-12 (dichlorodifluoromethane), which have historically been used as refrigerants, solvents, blowing agents for foams, and propellants in aerosol products.

Because of their stability, CFCs persist in the lower atmosphere and gradually migrate to the stratosphere, where ultraviolet radiation breaks them apart to release chlorine atoms. These atoms catalytically destroy ozone molecules in catalytic cycles, thinning the ozone layer. The resulting increase in ultraviolet-B radiation reaching the surface poses risks to human health and ecosystems.

In response, the Montreal Protocol, agreed in 1987 and subsequently amended, phased out production and consumption of CFCs and other ozone-depleting substances. The agreement promoted transitional substitutes such as HCFCs, which are less ozone-depleting, and later encouraged alternatives like hydrofluorocarbons (HFCs), which do not deplete ozone but have high global warming potential. Some uses persist, including certain inhalers and specialized equipment, but these are gradually being replaced.

Today, production of most CFCs has ceased under the Protocol. The ozone layer is slowly recovering, with regional variations in timing and pace. Legacy emissions and the long atmospheric lifetimes of CFCs mean that environmental impact persists, but overall progress shows a move toward restoration of pre-1980 ozone levels over coming decades.