Spatial variation in GHG emissions for U.S. soybean biodiesel supply chains

Abstract

Biofuels are widely promoted as an alternative to fossil fuels for decarbonizing transportation. However, concerns have been raised about the environmental integrity of these fuels. Most U.S. biofuel life cycle assessments (LCA) rely on large or national-scale assumptions that can overlook supply-chain variations. This study enhances the spatial resolution of U.S. soybean biodiesel LCA by integrating emissions data from county-level soybean production, supply-chain-specific transportation, and regional energy mixes. A least-cost optimization approach was applied to create subnational supply chains using complete U.S. soybean oil supply and demand. Then, emissions were aggregated to quantify cradle-to-processing gate global warming potential (GWP). Emissions ranged from 34-135 (avg. 58) gCO2eq MJ-1; excluding land use change (LUC), the range was reduced to 28-41 (avg. 33) gCO2eq MJ-1. Results showed that LUC largely drove variations in emissions. These results underscore the importance of spatial resolution and the contributions of LUC emissions in accurately assessing biodiesel emissions.