Increased estimates of air-pollution emissions from Brazilian sugar-cane ethanol

Accelerating biofuel production has been promoted as an opportunity to enhance energy security, offset greenhousegas emissions and support rural economies. However, large uncertainties remain in the impacts of biofuels on air quality and climate1,2. Sugar-cane ethanol is one of the most widely used biofuels, and Brazil is its largest producer3. Here we use a life-cycle approach to produce spatially and temporally explicit estimates of air-pollutant emissions over the whole life cycle of sugar-cane ethanol in Brazil. We show that even in regions where pre-harvest field burning has been eliminated on half the croplands, regional emissions of air pollutants continue to increase owing to the expansion of sugar-cane growing areas, and burning continues to be the dominant life-cycle stage for emissions. Comparison of our estimates of burning-phase emissions with satellite estimates of burning in São Paulo state suggests that sugar-cane field burning is not fully accounted for in satellite-based inventories, owing to the small spatial scale of individual fires. Accounting for this effect leads to revised regional estimates of burned area that are four times greater than some previous estimates. Our revised emissions maps thus suggest that biofuels may have larger impacts on regional climate forcing and human health than previously thought. Air-pollutant emissions from biofuel production and combustion may have significant impacts on climate and air quality. The change in vehicle emissions that would result from a large-scale conversion from gasoline to E85 (a blend of up to 85% ethanol with gasoline or another hydrocarbon) in the United States could have significant health consequences, by increasing tropospheric ozone concentrations4, for example. Monetizing the health and climate impacts of US ethanol emissions (fuel production and vehicle emissions) suggests that the use of corn ethanol has higher health costs than gasoline, whereas cellulosic ethanol may reduce health costs compared with gasoline use5. Although much has been learned about long-lived greenhousegas emissions from sugar-cane ethanol production6,7, emissions of other gases and aerosols remain relatively uncertain. Brazilian sugar-cane ethanol has potentially large life-cycle air-pollution emissions because many sugar-cane croplands are burned before harvest8,9. Epidemiological studies suggest that exposure to these emissions results in health impacts such as respiratory disease8,10,11. The radiative forcing of the emissions may also have significant regional climate impacts12. Although some regional governments have started to encourage farmers to gradually reduce field burning3, more than half of sugar-cane croplands continue to be burned13. Air pollution, which depends on the spatial and temporal distribution of emissions, is thus a crucial issue for sugar-cane