Gasohol is a term used for the mixture of 10% ethyl alcohol (also called ethanol or grain alcohol) with gasoline. Ethanol raises the octane rating of lead-free automobile fuel and significantly decreases the carbon monoxide released from tailpipes. It has also been promoted as a means of reducing corn surpluses. By 2001, 2.2 billion gal (8.3 billion l) were being produced a year and this number is expected to rise to 4.6 billion gal (17.4 billion l). However, ethanol also raises the vapor pressure of gasoline, and it has been reported to increase the release of "evaporative" volatile hydrocarbons from the fuel system and oxides of nitrogen from the exhaust. These substances are components of urban smog, and thus the role of ethanol in reducing pollution is controversial.