Ethanol causes ozone pollution

Researchers from Northwestern University have discovered that when residents of São Paulo chose gasoline over ethanol derived from sugar cane to fuel their vehicles, levels of ozone actually decreased.

The researchers set out to examine the effects of human behaviour at the pump on urban air pollution. During two episodes of high sugar prices in 2010 and again in 2011, the price of ethanol increased, causing consumers in São Paulo to switch their fuel usage to gasoline, or more than a million cars.

São Paulo has the world’s largest flexible-fuel vehicle fleet, with cars that can run on all gasoline, all ethanol or some mix of the two. Gasoline prices in Brazil are controlled by the government, and the domestic sugar price—and therefore the domestic price of ethanol—is determined by the world sugar price.

Their results surprised them: Local ozone levels dropped by 20 per cent while nitric oxide and carbon monoxide concentrations went up.

“Ozone and nitric oxide are both contributors to urban smog, so depending on how well a city is able to mitigate air pollution, ethanol may not be the ‘green fuel’ that it is often called,” said Franz M. Geiger, a professor of chemistry at Northwestern.

The study shows how pollution control requires a team that bridges atmospheric science and engineering, economics and statistics. “This work allows us to start thinking about the urban metabolism of Chicago, which is an emerging megacity surrounded by ‘corn country,’” Geiger said. “Ethanol from corn is a particularly intriguing option for future, possibly more competitive, energy markets. It’s an area we need to watch.”

 

Photo credit: Blog do Mílton Jung/Creative Commons

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