This table lists information on the main greenhouse gases, including their chemical formula, pre-industrial concentration, 1994 concentration, atmospheric lifetime, anthropogenic sources and global warming potential. These main gases include Carbon dioxide, Methane, Nitrous oxide, CFC-12, HCFC-22, Perfluoromethane, and Sulphur hexa-fluoride. The gas with the highest global warming potential is sulphur hexa-fluoride, which comes from dielectric fluid. However, this gas is present in the smallest concentration of the gases listed - only 0.032 parts per billion by volume. Carbon dioxide, on the other hand, has the lowest global warming potential – its value in this scale is one - but carbon dioxide has the highest concentration: 358 000 parts per billion by volume in 1994. This level had increased from a pre-industrial concentration of 278 000 parts per billion by volume. Concerning atmospheric lifetime, Perfluoromethane, which comes from the production of aluminium, has the longest atmospheric lifetime at 50 000 years, while HCFC-22 and methane have the shortest defined atmospheric lifetime, each with a lifetime of around 12 years. The lifetime value for carbon dioxide is variable due to the different rates of uptake by different sink processes.