Hydrochlorofluorocarbons, commonly known as HCFCs, are a group of man-made compounds containing hydrogen, chlorine, fluorine and carbon. They are not found anywhere in nature. HCFC production began to take off after countries agreed to phase out the use of CFCs in the 1980s, which were found to be destroying the ozone layer. Like CFCs, HCFCs are used for refrigeration, aerosol propellants, foam manufacture and air conditioning. Unlike the CFCs however, most HCFCs are broken down in the lowest part of the atmosphere, and pose a much smaller risk to the ozone layer. Unfortunately HCFCs are also very potent greenhouse gases, despite their very low atmospheric concentrations, measured in parts per trillion (million million).