Clearing the air on ethanol
Environmental Science and Technology Online Science News
April 18, 2007
When Mark Jacobson heard a venture capitalist tout ethanol fuel as a solution to air pollution last year, he was surprised-and intrigued. Jacobson, an atmospheric chemist at Stanford University, knew that air quality got worse during Brazil's big ethanol push in the 1970s and that the reason was still unclear.
As he soon learned, many of ethanol's backers are now pitching it as a clean-burning, healthy alternative to gasoline, in addition to promoting it as a homegrown fuel with potential CO2 savings. The idea is that ethanol burns cleaner than gas, making fewer unhealthy emissions and creating less smog. President Bush, biofuels industry groups, and even the American Lung Association of the Upper Midwest have promoted ethanol as good for public health.
Jacobson decided to use his sophisticated air-pollution model to put ethanol to the test. Would switching the U.S. fleet to white lightning make the country breathe easier?
His results, published today on ES&T's Research ASAP website (DOI: 10.1021/es062085v), show that ethanol is no silver bullet for health. Switching to E85 blends (85% ethanol, 15% gasoline) could result in slightly higher ozone-related mortality, hospitalization, and asthma (9% higher in Los Angeles and 4% higher in the U.S. as a whole), the study finds. Cancer rates would be similar for gasoline and E85.
"It's true that ethanol does decrease some pollutants, but it also increases some others," Jacobson says. Compared with gasoline, ethanol tends to produce less benzene and butadiene, but more acetaldehyde and formaldehyde, when burned.
The result: more ozone and about 185 more deaths per year across the U.S., with 125 of those in Los Angeles. Jacobson studied that city in depth because of its ongoing smog problem and found that it has the right atmospheric chemistry to make the ethanol switch particularly problematic.
Previous studies have estimated the pollution and health effects of burning ethanol, but Jacobson says those researchers simply scaled up tailpipe emissions and plugged those numbers into outdated formulas to calculate ozone changes and cancer rates. His atmospheric model, called GATOR-GCMOM, accounted for the transport of tailpipe emissions across the U.S. along with chemical transformations in the atmosphere-key components that had been neglected in previous studies.
The findings suggest that ethanol cannot be promoted simply as a boon to public health, Jacobson adds. Other factors need to be studied and weighed before ethanol use is made widespread, he says, such as greenhouse-gas emissions, U.S. dependence on foreign oil, and the environmental impacts of growing plants for ethanol.
Biofuels such as ethanol "simply have not been well studied yet," says Mark Delucchi, a transportation analyst at the University of California, Davis. With regard to climate, "We really don't know even the sign of the impacts, positive or negative," he says.
While research continues, ethanol production is ramping up. The U.S. Department of Agriculture's latest projections show corn planting skyrocketing to more than 90 million acres this year, 15% higher than last year and the most since World War II.
Even more could be coming. In January's State of the Union address, President Bush announced plans to reduce gasoline consumption by 20% in 10 years, and ethanol is a keystone in that plan. E85 works only in flex-fuel vehicles, of which there are at least 6 million on U.S. roads. E85 pumps, however, are concentrated in the upper Midwest, close to the corn.
California's Air Resources Board (CARB) is studying ethanol as part of Gov. Schwarzenegger's executive order calling for 10% less carbon in fuels by 2020. But the state is not yet rolling out the red carpet for ethanol. CARB applied for a waiver of the U.S. EPA's rule requiring 10% blends of ethanol during winter months and says it's considering ethanol's effects on air quality.
Environmental scientists should monitor changes in air quality as ethanol use ramps up, says Paul Lioy of the Center for Exposure and Risk Modeling at Robert Wood Johnson Medical School. "Any time you change a fuel, you're going to change things-we've seen it so many times," he says, citing the environmental effects of lead, sulfur, and methyl-tert-butyl ether (MTBE) in fuels.
"There will be issues to address with any biofuel," says Dan Kammen of the University of California, Berkeley. But even if ethanol does not improve air quality, he says, there are other reasons to consider it, such as global warming. Kammen recently received a large grant to study biofuels and has been prominent in the research community supporting ethanol, particularly cellulosic ethanol, for its potential carbon savings.
But rushing ahead to fix one problem can create another, cautions Hadi Dowlatabadi of the University of British Columbia (Canada). In a previous ES&T study, he found that a U.K. policy designed to reduce carbon emissions created air-quality problems by encouraging particulate-spewing diesel vehicles. He praised the new paper for "trying to point out an issue ahead of time".
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