Petroleum and gasoline consist of blends of over 250 diverse hydrocarbons. Many of these are toxic; some, such as benzene, are carcinogenic. Hydrocarbons escape into the air during refilling, from the gasoline tank and carburetor during normal operation, and from engine exhaust. Transportation sources account for 30-50% of all hydrocarbon emissions into the atmosphere.

Ozone is formed in air when hydrocarbons, carbon monoxide or nitrogen oxides react in the presence of sunlight and heat. This is of particular concern on warm, summer-like days when “smog” is prevalent. Ground level ozone causes human respiratory stress, and damages many plants, significantly reducing farm crop yields and the “health” of trees and other vegetation. However, ground level ozone does nothing to increase ozone concentration in the stratosphere, which protects the earth from the sun’s harmful ultraviolet radiation. Burning gasoline emits significant quantities of a wide range of hydrocarbons, whereas burning ethanol yields mainly unburned ethanol and aldehydes. Alcohols have much lower reactivities than gasoline hydrocarbons, whereas aldehydes are highly reactive. Several U.S.-based studies conclude that the overall ozone forming potential of ethanol-gasoline blends (with their higher volatility) is about the same as gasoline. In Canada, however, the volatility of ethanol blends must match normal gasoline, and therefore the ozone forming potential of ethanol blends will be reduced, overall.

Aldehyde emissions from ethanol blends are generally higher than those from gasoline. Formaldehyde, the major constituent in aldehyde emissions, is a suspected carcinogen. However, the catalytic converters used on all post-1987 vehicles reduce aldehyde emissions to near the level produced when unblended gasoline is combusted. The Royal Society of Canada has concluded that any increases are minute, and harmful effects are remote.

Carbon Monoxide
Carbon monoxide is a poisonous gas produced by incomplete combustion. Vehicles operating at colder temperatures (in winter months, during engine warm-up or in stop-and-go traffic) produce significant quantities of this deadly gas, which is of particular concern in urban areas. Although modern emission control systems have reduced the hazard from this gas, carbon monoxide levels still occasionally exceed the maximum acceptable level in some urban locations in Canada. U.S. data show that transportation sources account for over two-thirds of this pollutant. As a result, many U.S. cities have mandated the use of “oxygenated” gasolines, such as ethanol blends, to reduce carbon monoxide emissions. Many of Canada’s major urban areas would also need to utilize oxygenated gasoline if they were obliged to meet the more stringent U.S. standards.

Carbon Dioxide
Carbon dioxide, a normal product of burning fuel, is non-toxic, but contributes to the greenhouse effect (global warming). All petroleum (hydrocarbon) fuels cause increased atmospheric carbon dioxide levels because they represent the combustion of fossilized carbon. By contrast, using renewable fuels, such as ethanol, does not increase atmospheric carbon dioxide levels. The carbon dioxide formed during combustion is balanced by that absorbed during the annual growth of plants used to produce ethanol. In fact, renewable fuel technology can result in a net reduction in atmospheric carbon dioxide levels, by transforming carbon dioxide into organic matter that is returned to the soil, increasing soil fertility and reducing erosion.