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

Abstract

It has been proposed that lower NOX emission fuels such as ethanol can mitigate air pollution from vehicles burning oil-based hydrocarbons. Yet, existing modeling and laboratory studies, even those seeking to simulate the same environment, vary in their predictions of how gasoline/ethanol blends affect atmospheric pollutant concentrations, including ozone. Importantly, ambient concentrations have not been evaluated during an actual -as opposed to hypothetical -shift in fuel mix in a real-world environment. Here, we report the first such study, for the subtropical megacity of São Paulo, Brazil. We combine detailed street-hour level data on regulated pollutant concentrations, meteorology, and traffic with fuel shares from a consumer demand model to compare concentrations across subsamples that differ only in the fuel mix but are otherwise similar in meteorology, anthropogenic activity, and biogenic emissions. As the gasoline share of the bi-fuel light-duty vehicle fleet rose by 62 percentage points, we estimate a robust and statistically significant reduction of about 20% in ozone concentrations, and less precise increases in NO and CO concentrations. We propose that our "model-free" analysis potentially accounts for the interaction between anthropogenic and biogenic emissions and caution that successful strategies against ozone pollution require knowledge of the PRE-PRINT DATE: 18 February, 2014 Ozone levels are relatively high in São Paulo, with hourly concentrations above 75 and 125 g/m 3 , respectively, 2.7 and 5.3 times more likely than for PM10 in our sample. Light transportation is a key contributor to air pollution in this gridlocked metropolis [1][2][3] , with large public health implications [4][5][6][7] . In 2011, 40% of the city's 6 million active light-duty vehicles -likely accounting for over one-half of all light vehicle distance traveled -possessed bi-fuel capability. This capability allowed consumers to choose between gasoline (an E25 or E20 blend) and ethanol E100 at the pump 8 , as both fuels were ubiquitous among São Paulo's retailers 9,10 . In recent years, governmentcontrolled gasoline prices held steady whereas market-set sugarcane ethanol prices tracked the significant swings in the world price of sugar 8,10 . This empirical setting provides a rarely observed opportunity to examine whether urban air pollution was impacted by emissions that transitioned between gasoline and ethanol -both combustion and evaporation. São Paulo city currently features clogged hypothetical large-scale switch from a fossil fuel over to a biofuel in a large urban center. Analysis of Concentrations, Traffic, and Meteorology at Street-Hour LevelOur study cross-examines a large amount of measured data, detailed at the streethour level (Fig. 2), from several sources: (i) concentrations of regulated "priority" . We combine the extensive pollutantmeteorology-traffic data with: (iv) weekly gasoline and ethanol prices at the pump, obtained from the National Agency for Oil, Biofuels and Natural Gas (ANP) 10 , which in tu...

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