Ethanol to gas switch boosts tiny pollution particles

(Credit: Julia P/Flickr)

When high ethanol prices pushed drivers in São Paulo, Brazil to switch to filling up with gasoline, the concentration of ultrafine particles less than 50 nanometers in diameter increased by one-third, research suggests.

Environmental protection agencies across the world currently do not measure or regulate particles of this size, which studies have shown to be harmful to human health.

“We studied São Paulo, but there are many North American cities, including Chicago, with similar air chemistry…”

The research team also found when São Paulo drivers—some two million of them—switched back to ethanol because prices had gone down, the concentration of ultrafine particles also went down. This lockstep movement illustrates a very tight correlation between fuel choice and nanoparticles in the air.

“We studied São Paulo, but there are many North American cities, including Chicago, with similar air chemistry, especially spring through fall,” says Franz M. Geiger, professor of chemistry in Northwestern University’s Weinberg College of Arts and Sciences.

“The push we are seeing in large cities away from gasoline and toward vehicles powered by ethanol, electricity or a mix of the two will result in a reduction of these ultrafine particles. This likely comes with a health benefit—these particles, below one micron, have the potential to get deeply into your lungs,” he says.

Geiger and Alberto Salvo, an associate professor of economics at the National University of Singapore, led the study—the team’s second with São Paulo big data. The fact that São Paulo consumers can and do switch between fuels for reasons unrelated to air quality provided the researchers with a real-world laboratory for studying the effects of human behavior at the fuel pump on urban air pollution.

The prospect of increased biofuel use and mounting evidence on ultrafines’ health effects make the results policy relevant, the authors write.

“With this knowledge, we hope more money and human resources will be invested in trying to understand and possibly monitor these ultrafine particles,” says Salvo, who formerly was with Northwestern’s Kellogg School of Management. “The big unknown is what type of particles are the most harmful to health.”

The interdisciplinary team conducted a regression analysis of traffic, consumer behavior, aerosol particle size, and meteorological data from January, 2011 through May, 2011. The data studied was from before, during, and after the time of a major fuel switch due to a large fluctuation in ethanol prices.

The researchers also found the choice of fuel had no effect on the concentration of larger particles. These particles include fine particulate matter 2.5 microns in diameter (PM2.5) down to particles 100 nanometers in diameter. The United States and many other countries regulate PM2.5, but particles smaller than PM2.5 are not regulated.

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Geiger and Salvo were fortunate to have access to aerosol particle size distribution data from an unrelated research project overseen by Paulo Artaxo and Joel Brito at the University of São Paulo. Artaxo and Brito’s experiments captured data from before, during, and after the major fuel switch.

The study builds on an earlier study in which Geiger and Salvo found that an increase in ethanol use resulted in a significant increase in ozone concentrations in São Paulo. Officials, Geiger says, will need to weigh the increase in ozone against the decrease in nanoparticles when ethanol is used.

Next, for the third chapter of the story, the research team would like to determine what happened in terms of health outcomes in São Paulo as cars switched out of gasoline to ethanol and back to gasoline.

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. Brazil’s government controls the gasoline prices, and the world sugar price controls the domestic price of ethanol, which is made out of sugarcane.

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The Initiative for Sustainability and Energy at Northwestern University (ISEN); the dean’s office of the Kellogg School of Management; the W Awards Program at Northwestern’s Weinberg College of Arts and Sciences; a grant from the dean’s office of the Faculty of Arts and Social Sciences, National University of Singapore; and grants from the São Paulo Research Foundation supported this research.

The study appears in the journal Nature Communications.

Source: Northwestern University