A Northwestern University study by an economist and a chemist reports that when fuel prices drove residents of So Paulo, Brazil, to mostly switch from ethanol to gasoline in their flexible-fuel vehicles, local ozone levels dropped 20 percent. At the same time, nitric oxide and carbon monoxide concentrations tended to go up.
The four-year study is the first real-world trial looking at the effects of human behavior at the pump on urban air pollution. This empirical analysis of atmospheric pollutants, traffic congestion, consumer choice of fuel and meteorological conditions provides an important tool for studying other large cities, such as Chicago, New York, London and Beijing. Previous studies mainly have consisted of computer simulations of atmospheric chemical reactions based on tailpipe emissions studies.
"Individuals often don't realize it, but in the aggregate, you can have a real impact on the environment," said Alberto Salvo, formerly with Northwestern's Kellogg School of Management and now an associate professor of economics at the National University of Singapore. "In So Paulo, there were more than a million cars switching from ethanol to gasoline in the same season, and we found that ozone levels went down. We didn't expect this, but it is a precise result."
Salvo teamed up with chemist Franz M. Geiger to help him tease the air quality picture out of the highly complex chemistry using statistical methods. The results of their study will be published April 28 in the journal Nature Geoscience.
Salvo and Geiger used fuel sales data and 14,000 consumer surveys to predict the magnitude of the fuel shift from ethanol to gasoline and back over the course of 30 months. They next determined the change in pollutant concentrations based on the predicted fuel mix, meteorology data and traffic levels across 600 miles of roads and discovered that ozone levels decreased significantly relative to the rise of gasoline usage.
|Contact: Megan Fellman|