Application of the roundtable on sustainable biofuels method to regional differences in nitrous oxide emissions for the rapeseed hydrotreated renewable jet life cycle

© 2014 Elsevier Ltd. All rights reserved. Hydrotreated Renewable Jet (HRJ) fuel has increasingly become important for the aviation sector to address energy security and climate change mitigation. Rapeseed (Brassica Napus) is a favored candidate feedstock for HRJ because of its high quality oil content and agroeconomic benefit to replace the fallow period in wheat/fallow rotations. We conducted research to evaluate regional differences in nitrous oxide (N2O) emissions for rapeseed cultivation in several counties in 10 states in the United States (U.S.). The Roundtable on Sustainable Biofuels (RSB) methodology was applied, and results were compared to the Intergovernmental Panel on Climate Change (IPCC) guidelines. In this study, yield, nitrogen fertilizer rate, and types were held constant for all locations in order to understand the similarities and differences in the RSB and IPCC methods for estimating N2O emissions. From the results, the RSB-calculated N2O emissions varied for different U.S. states, though regional differences were very small, 0.72-0.73 kg N2O Mg-1seed, while N2O emissions from IPCC method were the same for all sites, 0.87 kg N2O Mg-1seed. The difference between the RSB and IPCC methods is caused by the indirect N2O emissions from ammonia emissions and nitrate leaching. However, the influence of indirect effect is relatively small compared to overall N2O emissions. The utilization of the RSB method may not be justified for estimating regional variations in N2O emissions. As a consequence, the preliminary greenhouse gas (GHG) of rapeseed HRJ fuel using the RSB method in several locations had small differences in result, 42.7-43.0 g CO2 eq/MJ compared to 45.9 g CO2 eq/MJ using the IPCC method