The concentration of ultrafine particles less than 50 nanometers in diameter rose by one-third in the air of São Paulo, Brazil, when higher ethanol prices induced drivers to switch from ethanol to gasoline, according to a new study by a Northwestern University chemist, a National University of Singapore economist and two University of São Paulo physicists.
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. The study is published in the journal Nature Communications.
Geiger and Alberto Salvo, an associate professor of economics at the National University of Singapore, led the study—their second with São Paulo big data. In the first, they found that when fuel prices drove residents of São Paulo, Brazil, to mostly switch from ethanol to gasoline in their flexible-fuel vehicles, local ozone levels dropped 20%. At the same time, nitric oxide and carbon monoxide concentrations tended to go up. Officials, Geiger said, will need to weigh the increase in ozone against the decrease in nanoparticles when ethanol is used.
The ability of São Paulo consumers to 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.
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 US. and many other countries regulate PM2.5, but particles smaller than PM2.5 are not regulated.
Geiger and Salvo had 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. They are co-authors of the Nature Communications paper, along with Geiger and Salvo.
For the next phase of research, the 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. Gasoline prices in Brazil are controlled by the government, and the domestic price of ethanol, which is made out of sugarcane, is determined by the world sugar price.
Support for the research was provided by 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; the dean’s office of the Faculty of Arts and Social Sciences, National University of Singapore (grant R-122-17 000-187-133); and the São Paulo Research Foundation (grants 2013/05014-0 and 2013/25058-1).
Alberto Salvo, Joel Brito, Paulo Artaxo, and Franz M. Geiger (2017) “Reduced ultrafine particle levels in Sao Paulo’s atmosphere during shifts from gasoline to ethanol use”