Ethanol, also called ethyl alcohol, grain alcohol, and drinking alcohol, is an organic compound composed of carbon, hydrogen and oxygen. It is a volatile, flammable, colorless liquid with a characteristic wine-like odor and a pungent taste. The largest and fastest growing application is as a fuel, or gasoline fuel additive, for automobiles and other road vehicles. It is also the active ingredient in alcoholic drinks, and is used as an antiseptic and disinfectant, as a chemical solvent, and as an input for the production of other organic compounds.
Ethanol is attractive as a fuel both because it can be a renewable resource and because it reduces harmful emissions of carbon monoxide, particulate matter, nitrogen oxides and some other pollutants. Currently the most common production processes use yeast to ferment the starch and sugars in corn, sugar cane and sugar beets. However, it is also produced in large quantities from petroleum, through the hydrolysis of ethylene, a large volume petrochemical.
Unfortunately, there are also some important disadvantages, for the vehicles in which it is used, for air quality, and for the efficient use of increasingly scarce natural resources. With regard to vehicles, it can damage engines and reduce their performance, depending on the age and type of vehicle, because of its tendency to absorb water from the air, and it can cause deterioration of the plastic and rubber components in fuel systems. Moreover, ethanol degrades relatively rapidly, making its long-term storage difficult.
With regard to air quality, it yields many of the products of incomplete combustion produced by gasoline as well as significantly greater amounts of formaldehyde and related chemicals such as acetaldehyde, and it can generate more ground-level ozone than gasoline.
With regard to the efficient use of increasingly scarce natural resources, producing ethanol is fairly energy-intensive, although progress has been made on this in recent years and it appears that it is now usually 'energy positive' (i.e., more energy is obtained from it than is used to produce it). However, producing it from corn and other crops consumes vast quantities of farmland and often increasingly scarce groundwater that could be used for food production, thereby driving up food costs. It also requires large quantities of synthetic fertilizers, for which there could be a long-term shortage.