HOW DOES ETHANOL
"LET'S CLEAR THE AIR"?
Most liquid fuels (gasoline, diesel, natural gas, propane) come from fossil hydrocarbons. Unlike them, ethanol is produced from renewable biological feedstocks, such as agricultural crops and forestry by-products. Carbon dioxide is released into the atmosphere when ethanol (like other fuels) is burned in an automobile engine. However, this carbon dioxide is recycled into organic tissue during plant growth. Only about 40 percent or less of the organic matter is actually removed from farm fields for ethanol production. The rest is returned to the soil as organic matter, increasing fertility and reducing soil erosion. With modern conservation farming practices, this soil organic-matter will build up, representing a net removal of carbon dioxide from the atmosphere. An increase of only 1% in the soil organic matter level means an atmospheric reduction of over 40 tonnes of carbon dioxide per hectare of farm land.
Canada has vast areas of agricultural cropland. Most of these soils could benefit from increasing soil organic matter by several percentage points. Ethanol use in gasoline has tremendous potential for a net reduction in atmospheric carbon dioxide levels.
Carbon monoxide, formed by the incomplete combustion of fuels, is produced most readily from petroleum fuels which contain no oxygen in their molecular structure. Because ethanol and other oxygenated compounds contain oxygen, their combustion in automobile engines is more complete. The result is a substantial reduction in carbon monoxide emissions. Research shows that reductions range up to 30%, depending on type and age of automobile, the automobile emission system used, and the atmospheric conditions in which the automobile operates.
Because of health concerns over carbon monoxide, the 1990 amendments to the U.S. Clean Air Act mandate the use of oxygenated gasolines in many major urban centres during the winter (when atmospheric carbon monoxide levels are highest) to reduce this pollution.
Other Octane Additives
Because of its high octane rating, adding ethanol to gasoline can permit the reduction or removal of aromatic hydrocarbons (such as benzene), and other hazardous high-octane additives commonly used to replace tetra-ethyl lead in Canadian gasoline.
Because of its effect in reducing hydrocarbons and carbon monoxide in exhaust, adding ethanol to gasoline results in an overall reduction in exhaust ozone-forming potential.
Ethanol has no significant effect on emissions of nitrous oxide, another common contributor to atmospheric ozone.
Adding ethanol to gasoline can potentially increase the volatility of gasoline. This potential is controlled if all ethanol-blended gasoline sold in Canada meets the volatility standards required for other types of gasoline. In contrast, the U.S. Clean Air Act allows gasohol (gasoline plus 10% ethanol) to have a higher volatility than that of gasoline. This results in greater volatile organic compounds emissions. Therefore, the Canadian ethanol blend has less potential to form ozone than the American counterpart.
Adding of ethanol to gasoline does create slightly greater amounts of aldehydes during fuel combustion. Yet the resulting concentrations are extremely small and are effectively reduced by the three-way catalytic convertors in the exhaust systems of all recent-model cars. The Royal Society of Canada termed the possibility of negative health effects caused by aldehyde emissions with the use of ethanol-blended gasoline as being remote.