A series of compounds of entirely anthropogenic origin that were used in industrial applications throughout most of the twentieth century. The major CFCs are CFC-11 (CFCl3) and CFC-12 (CF2Cl2). These compounds have long atmospheric lifetimes (many decades) enabling them to be transported to the stratosphere. The discovery that liberation of chlorine from these species was responsible for the appearance of the antarctic ozone hole each spring led to the introduction of the Montreal Protocol, which banned the use of these species. Although they are no longer in use, their long lifetimes will lead to a very slow removal from the atmosphere.