Reduction in local ozone levels in urban São Paulo due to a shift from ethanol to gasoline use

Abstract

Ethanol-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.

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Figure 1: Shifting fuel quantities and prices between October 2008 and July 2011.
Figure 2: Street-hour analysis of concentrations and controls.
Figure 3: Gradual transitions between ethanol and gasoline in bi-fuel vehicles.
Figure 4: Estimated changes in O3, NO, and CO concentrations as the gasoline share, stgas, rose by 62 percentage points.

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Acknowledgements

We gratefully acknowledge numerous people from CETESB, INMET, CET and ANP for generously sharing their data; CBN Notícias for sharing their newscasts; and Raízen for sharing access to their fuelling stations. In particular, we thank W. Baptista, C. Costa, A. Dall’Antonia Jr, F. Henkes, M. Kuromoto, C. Lacava, D.G. Medeiros, R.C. Melo, R. dos Santos and T. P. Senaubar. We thank T. Aguirre for summarizing descriptive CETESB and CPTEC weather reports, M. Peterson for preparing a literature review as well as an initial written and graphical description of the pollutant and meteorological data, and S. Ritchey for listing the GPS coordinates of road segments. We thank S. Budanova, E. Lehman and C. Maalouf for research assistance, as well as J. Brito, M. Busse, J. He, E. Mansur and S. McRae for helpful comments. A.S. acknowledges support from the Initiative for Sustainability and Energy at Northwestern University (ISEN) and from the Dean’s Office at the Kellogg School of Management, Northwestern University. F.M.G. thanks the NSF Atmospheric and Geospace Science division for support under grant # NSF ATM-0533436 and gratefully acknowledges support from an Irving M. Klotz professorship in physical chemistry.

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A.S. conceived the research; A.S. and F.M.G. analysed the data and wrote the paper.

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Correspondence to Alberto Salvo.

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Salvo, A., Geiger, F. Reduction in local ozone levels in urban São Paulo due to a shift from ethanol to gasoline use. Nature Geosci 7, 450–458 (2014). https://doi.org/10.1038/ngeo2144

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