Does the concentration of carbon monoxide produced by engines vary?
Yes, CO emitted from the tailpipe of engines burning gasoline, diesel, or LPG (propane) varies from over 100,000 parts per million (ppm) to less than 15 ppm. In 1968 the EPA regulated CO emissions from on-road motor vehicles. Engines used indoors were not originally regulated. Recent regulations affect small engines such as those used on lawn mowers, chain saws, weed eaters, electric generators, water pumps, and boats, although the regulations for small engines will continue to allow considerably higher CO concentrations than the tighter regulations for on-road motor vehicles. Why does the concentration of CO produced vary? Carbon monoxide is produced during incomplete combustion. Anything that leads to incomplete combustion increases CO production. Two major causes are a rich fuel mixture (more fuel than is needed), or restricted air supply (dirty or plugged air filter). A gasoline engine producing 10,000 ppm CO at the ideal air-fuel ratio will produce over 60,000 ppm when the fuel is
