Overview article:
Ethanol Fuels Ozone IncreaseEmpirical study unexpectedly finds that switch from gasoline to ethanol in flex-fuel vehicles raises ozone levelsA 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.”
original article:
Reduction in local ozone levels in urban São Paulo due to a shift from ethanol to gasoline useEthanol-based vehicles are thought to generate less pollution than gasoline-based vehicles, because ethanol emissions contain lower concentrations of mono-nitrogen oxides than those from gasoline emissions. However, the predicted effect of various gasoline/ethanol blends on the concentration of atmospheric pollutants such as ozone varies between model and laboratory studies, including those that seek to simulate the same environmental conditions. Here, we report the consequences of a real-world shift in fuel use in the subtropical megacity of São Paulo, Brazil, brought on by large-scale fluctuations in the price of ethanol relative to gasoline between 2009 and 2011. We use highly spatially and temporally resolved observations of road traffic levels, meteorology and pollutant concentrations, together with a consumer demand model, to show that ambient ozone concentrations fell by about 20% as the share of bi-fuel vehicles burning gasoline rose from 14 to 76%. In contrast, nitric oxide and carbon monoxide concentrations increased. We caution that although gasoline use seems to lower ozone levels in the São Paulo metropolitan area relative to ethanol use, strategies to reduce ozone pollution require knowledge of the local chemistry and consideration of other pollutants, particularly fine particles.
