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Greenhouse gas accounting procedures may overlook bio-derived aviation fuel

Low carbon fuel policies are intended to reduce greenhouse gas (GHG) emissions from transportation. However, rigid carbon intensity (CI) accounting procedures in current policies may limit CI responsiveness across candidate sites and facilities.

Work in the journal ACS Sustainable Resource Management examines a hypothetical biomass-to-sustainable aviation fuel (SAF) process to demonstrate how GHG accounting requirements drive estimates of biofuel CI and to explore potential CI and financial implications of scenario-specific life cycle assessment (LCA).

The CI of hypothetical SAF produced from miscanthus via the alcohol-to-jet (ATJ) pathway was calculated according to specifications from three low-carbon fuel policies (U.S. Renewable Fuel Standard (RFS), Canada Clean Fuel Regulations (CFR), and California Low-Carbon Fuel Standard (LCFS), and the 45Z tax credit.

These were compared against modeling results tailored to specific feedstock-to-fuel scenarios (scenario-specific LCA) defined by feedstock and facility siting and feedstock split ratio (the proportion of miscanthus allocated to fuel production vs. electricity).

GHG accounting using the CFR/LCFS can reasonably account for distinct levels of net electricity production by a biorefinery, but only the CFR yields similar CI sensitivity to spatially explicit factors as scenario-specific LCA. Most GHG accounting frameworks do not capture CI variation across candidate sites in the United States.

This work demonstrates the importance of LCA methodological specifications in low-carbon fuel policies and tax credits and illustrates that policies that enable scenario-specific CI calculations could enhance crediting accuracy and more effectively support the implementation of low-emission practices.