How is Carbon Monoxide Formed?
A. Carbon monoxide results from incomplete combustion of fuel and is emitted directly from vehicle tailpipes. Incomplete combustion is most likely to occur at low air-to-fuel ratios in the engine. These conditions are common during vehicle starting when air supply is restricted (“choked”), when cars are not tuned properly, and at altitude, where “thin” air effectively reduces the amount of oxygen available for combustion (except in cars that are designed or adjusted to compensate for altitude). Nationwide, two-thirds of the carbon monoxide emissions come from transportation sources, with the largest contribution coming from highway motor vehicles. In urban areas, the motor vehicle contribution to carbon monoxide pollution can exceed 90 percent.
