Ethanol, often promoted as a clean-burning, renewable fuel that could help wean the nation from oil, would likely worsen health problems caused by ozone, compared with gasoline, especially in winter, according to a new study led by Stanford researchers.
Ozone production from both gasoline and E85, a blend of gasoline and ethanol that is 85 percent ethanol, is greater in warm sunny weather than during the cold weather and short days of winter, because heat and sunlight contribute to ozone formation. But E85 produces different byproducts of combustion than gasoline and generates substantially more aldehydes, which are precursors to ozone.
"What we found is that at the warmer temperatures, with E85, there is a slight increase in ozone compared to what gasoline would produce," said Diana Ginnebaugh, a doctoral candidate in civil and environmental engineering, who worked on the study. She will present the results of the study on Tuesday, Dec. 15, at the American Geophysical Union meeting in San Francisco. "But even a slight increase is a concern, especially in a place like Los Angeles, because you already have episodes of high ozone that you have to be concerned about, so you don't want any increase."
But it was at colder temperatures, below freezing, that it appeared the health impacts of E85 would be felt most strongly.
"We found a pretty substantial increase in ozone production from E85 at cold temperatures, relative to gasoline when emissions and atmospheric chemistry alone were considered," Ginnebaugh said. Although ozone is generally lower under cold-temperature winter conditions, "If you switched to E85, suddenly you could have a place like Denver exceeding ozone health-effects limits and then they would have a health concern that they don't have now."
The problem with cold weather emissions arises because the catalytic converters used on vehicles have to warm up before they reach full efficiency. So until they
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