Possible greenhouse effects of tetrafluoromethane and carbon dioxide emitted from aluminum production

Tetrafluoromethane (CF4) is an extremely stable gas which strongly absorbs infrared radiation at 8 μm, and therefore is capable of influencing the greenhouse effect. No natural sources have been identified, and the major anthropogenic source appears to be the electrolytic smelting of alumina to produce aluminum. Measurements of CF4 concentrations in the atmosphere are reviewed, and these are combined with aluminum production rates to provide an estimate of 1.3–3.6 kg of CF4 emitted per ton of aluminum produced for the period up to 1985. Aluminum production also requires large amounts of electrical energy, leading to the emission of as much as 22 tons of carbon dioxide per ton of aluminum due to fossil fuel combustion in power plants. The present day contribution of hydroelectric power reduces this figure to about 14 tons of carbon dioxide per ton of aluminum. An estimate of the relative radiative trapping of CF4 and CO2 emitted in aluminum production during this same period (1900–1985) indicates that the effect of CF4 is about one-third that of the CO2 formed by aluminum production. However, the emission of fluorocarbons from modem aluminum electrolysis cells is much lower than previous estimates indicate, and this factor is considered in estimating potential long-term global warming effects of CF4 and CO2 from aluminum production. Possible processes leading to removal of CF4 from the atmosphere are described.