Encyclopedia of energy, volume 2: Ec-Ge. Cleveland CJ, Ayres, RU, Costanza R, Goldemberg J, Ilic M, Jochem E, Kaufmann R, Lovins A, Munasinghe M, Pachauri R, Pardo C, Peterson P, Schipper L, Slade M, Smil V, Worrell E, eds. Boston, MA: Elsevier Academic Press, 2004 Jan; 2:821-830
Since 1979, oxygenates as gasoline additives have been used in limited areas of the United States as octane enhancers to replace lead at levels around 2 to 8% by volume. During the 1980s, oxygenates came into wider use as some states implemented oxygenated gasoline programs for the control of carbon monoxide air pollution in cold winter. Oxygenates were added to conventional gasoline nationally at higher percentages with the passage of the 1990 Clean Air Act (CAA), which required that oxygenates be added either seasonally (15% MTBE by volume) or year-round (11% MTBE by volume) to gasoline in specific parts of the country where carbon monoxide in the winter or concentrations of ozone in the summer exceed their respective National Ambient Air Quality Standards (NAAQS).