The combination of ethanol and gasoline results in overall increases in smog-producing volatile organic compounds compared with either pure ethanol or pure gasoline. However, this can be overcome by blending ethanol with a gasoline that has been manufactured to have low volatility.

A high-ethanol fuel such as E-85 also produces lower levels of nitrogen oxides and toxic hydrocarbons such as benzene (a carcinogen) than gasoline does. Although E-85 produces higher levels of formaldehyde and other toxic aldehydes, the resulting concentrations are small and are effectively removed by catalytic converters in recent-model cars.