Carbon Monoxide High levels of carbon monoxide in automobile exhaust are a health hazard. Carbon monoxide emissions are greatest with cold engines and cold outside temperatures. If Canada used the same air quality standards as the U.S., the use of oxygenated gasolines would be mandatory in many Canadian cities as well. Carbon monoxide emissions are lower with fuel injected engines, than with carburetted engines, but this is only after the engines are fully warmed up. In many cities, in winter, this may rarely occur with commuter cars.
Carbon monoxide is also an ozone precursor.
U.S. studies have found that ethanol-blended gasoline, on balance, is mildly beneficial with respect to its contribution to ozone formation, compared to gasoline. But U.S. ethanol-blended gasoline is different than in Canada. This increases evaporative emissions and the potential for ozone formation. In most of Canada, including Ontario, ethanol-blended gasoline must meet all federal gasoline standards, including that for volatility. There is no Canadian waiver.