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Ethanol Fuels Ozone Increase

Empirical study unexpectedly finds that switch from gasoline to ethanol in flex-fuel vehicles raises ozone levels

by Mitch Jacoby
May 5, 2014 | A version of this story appeared in Volume 92, Issue 18

A multiyear analysis of air quality, economics, and consumer behavior found that when fluctuations in the relative prices of fuels between 2009 and 2011 led a large fraction of drivers in São Paulo, Brazil, to switch from ethanol to gasoline in flexible-fuel vehicles, local ozone concentrations fell by 20%. The study, which is the first of its kind to evaluate real-world multivariable data, as opposed to atmospheric modeling predictions, also found that the fuel switch tended to cause an increase in nitric oxide and CO levels (Nat. Geosci. 2014, DOI: 10.1038/ngeo2144). The analysis, which was conducted by economist Alberto Salvo of the National University of Singapore and chemist Franz M. Geiger of Northwestern University, accounts for numerous meteorological variables yet contradicts simulation results obtained with computer models tailored for conditions in São Paulo. Commenting in Nature Geoscience, Sasha Madronich of the National Center for Atmospheric Research notes that this study “should be viewed as a gold standard for the type of analysis needed to evaluate the reliability of atmospheric chemistry models designed to simulate the effects of the transportation sector on air quality.”


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