When in the subtropical megacity of Sao Paulo, Brazil, the share of dual-fuel vehicles burning gasoline rose from 14% to 76%, dropping ethanol fuel usage to about a quarter, the local ozone levels fell by 20%, reports an article published online in Nature Geoscience. The shift in fuel usage was triggered by fluctuations in relative prices between 2009 and 2011, and the study finds that the shift to more gasoline use not only reduced ozone pollution, but also led to rising levels of nitric oxide and carbon monoxide in the local atmosphere.

Alberto Salvo and Franz Geiger estimated the magnitude of the fuel shift from ethanol to gasoline based on data on fuel sales and consumer surveys. They then assessed its impact on air quality from measurements of traffic levels, meteorology and pollutant concentrations, and found that a significant decrease in local ozone levels accompanied the relative rise of gasoline usage. They note, however, that their data are restricted to the Sao Paulo metropolitan area, and effects of fuel usage may depend on local atmospheric composition, in particular other pollutants such as fine particles.

In an accompanying News and Views article, Sasha Madronich writes: “The empirical analysis presented […] should be viewed as a gold standard.”