Using satellite image-based maps to improve sugarcane straw burning emission estimates in the state of São Paulo, Brazil

Abstract:

Since the last decade, the global demand for biofuel production has been increasing every year due to the growing need for energy supply security and mitigation of greenhouse gases (GHG). Currently, sugarcane ethanol is one of the most widely used biofuels and Brazil is already the world’s largest sugarcane producer, devoting almost 50% of it to ethanol production. The state of São Paulo is the major sugarcane producer in this country, with a cultivated area of about 5.4 Mha in 2011. Approximately 2 million hectares were harvested annually from 2006 to 2011 with the pre-harvest straw burning practice, which emits trace gases and particulate material to the atmosphere. The assessment and monitoring of sugarcane burning impacts are fundamental in order to mitigate the negative impacts of pre-harvest burning and consolidate the environmental benefits of sugarcane ethanol. Although some official inventories created by the Brazilian government have indicated the prevalence of emissions from sugarcane straw burning in total agricultural residue emissions, specific information about emissions of gases and aerosols during pre-harvest burning of sugarcane is still scarce in Brazil. This study aimed to contribute to the improvement of estimates of emissions from sugarcane burning through the use of specific parameters for sugarcane straw burning and a method which has avoided underestimations resulting from the unique characteristics of this type of biomass fire. In this investigation, emissions of several air pollutants released by sugarcane burning during the harvest season were estimated through the integrated use of remote sensing based maps of sugarcane burned area and a numerical tool for the state of São Paulo from 2006 to 2011. Average estimated emissions (Gg/year) were 1,130 ± 152 for CO, 26 ± 4 for NO_X, 16 ± 2 for CH₄, 45 ± 6 for PM_2.5, 120 ± 16 for PM₁₀ and 154 ± 21 for NMHC (non-methane hydrocarbons). An intercomparison among annual emissions from this study and annual emissions from four other different approaches indicated that the estimates obtained by satellite fire detection or low spatial resolution approaches tend to underestimate sugarcane burned area. Overall, our results also indicated that government actions to reduce sugarcane straw burning emissions are becoming effective.