chlorofluorocarbon

A class of synthetic chemicals that are odourless, non-toxic, non-flammable, and chemically inert. The first CFC was synthesized in 1892, but no use was found for it until the 1920s. Their stability and apparently harmless properties made CFCs popular as propellants in aerosol cans, as refrigerants in refrigerators and air conditioners, as degreasing agents, and in the manufacture of foam packaging. They are now known to be partly responsible for the destruction of the ozone layer. In 1987, an international agreement called the Montréal Protocol was established; it was one of the first global environmental treaties and it banned the use of chemicals responsible for ozone damage, such as CFCs in aerosols and refrigerants.

When CFCs are released into the atmosphere, they drift up slowly into the stratosphere, where, under the influence of ultraviolet radiation from the Sun, they react with ozone (O₃) to form free chlorine (Cl) atoms and molecular oxygen (O₂), thereby destroying the ozone layer which protects the Earth's surface from the Sun's harmful ultraviolet rays. The chlorine liberated during ozone breakdown can react with still more ozone, making the CFCs particularly dangerous to the environment. CFCs can remain in the atmosphere for more than a hundred years. Replacements for CFCs are being developed, and research into safe methods for destroying existing CFCs is being carried out.