A group of chemicals composed only of carbon and fluorine. These chemicals (mainly CF ₄ and C ₂ F ₆ ) were introduced as alternatives, along with hydrofluorocarbons, to ozone-depleting substances. In addition, PFCs are emitted as by-products of industrial processes and are also used in manufacturing. PFCs do not damage the stratospheric ozone layer, but they are powerful greenhouse gases: CF ₄ has a global warming potential (GWP) of 7,390 and C ₂ F ₆ has a GWP of 12,200. The GWP is from the Fourth Assessment Report of the IPCC (AR4). These chemicals are mostly man-made, although there is a small natural source _CF4