This document describes the development and outcomes of a comprehensive analysis to quantify the climate impact reduction of Sustainable Aviation Fuels (SAFs). Firstly, it is shown that existing Life Cycle Analyses (LCAs) exclude or do not properly model pump-to-wake (PtW) non-𝐶𝑂2 effects resulting from 𝑁𝑂𝑥 & 𝐻2𝑂 emissions and contrail formation, of both Conventional Jet Fuel (CJF) as well as SAF. To this end, a method is developed with which these PtW emissions are thoroughly quantified and incorporated into an existing LCA.

The method is designed to answer the following research question: ”What is the potential climate impact reduction of SAF in aviation?” and is divided into a well-to-pump (WtP) and a pump-towake (PtW) analysis. The WtP values are taken from literature (the CORSIA default values [3]) and indicate how much 𝐶𝑂2-equivalent (𝐶𝑂2𝑒) emissions are made for the production & transport of 1 𝑀𝐽 (unit of energy) of CJF and SAF, in gram: [𝑔𝐶𝑂2𝑒/𝑀𝐽]. For the PtW values, the 𝐶𝑂2 emissions released during the combustion of 1 𝑀𝐽 of SAF or CJF of 70.2 & 73.3 [𝑔𝐶𝑂2 /𝑀𝐽] respectively, are multiplied with a 𝐶𝑂2𝑒 factor for both SAF as well as CJF. This 𝐶𝑂2𝑒 factor is a ratio that evaluates the climate impact caused by all aviation emissions & effects (𝐶𝑂2, 𝑁𝑂𝑥, 𝐻2𝑂 & contrails) relative to that of 𝐶𝑂2. The climate impact is quantified using the Global Warming Potential (GWP) and Average Temperature Response (ATR) climate metrics over a given time horizon (20, 50 & 100 years), which analyze a radiative forcing (RF) and a temperature change (Δ𝑇) response respectively. The RF & Δ𝑇 responses are generated for a baseline CJF scenario as well as a SAF scenario using the non-linear climate chemistry model AirClim. All important aspects of SAF relative to CJF are accounted for: the dissimilar energy density and thus fuel flows, the different 𝐸𝐼𝐻2𝑂 & 𝐸𝐼𝐶𝑂2 , the different 𝐸𝐼𝑠𝑜𝑜𝑡 and thus contrail characteristics, and the similar 𝐸𝐼𝑁𝑂𝑥 . Finally, the WtP part is added to the PtW part to be able to quantify SAF’s well-to-wake (WtW) climate impact reduction potential. The results of this new analysis indicate that:
• Uponinclusion of PtW non-𝐶𝑂2 effects into the CORSIA SAF LCA from Prussi et al. (2021), the lifecycle 𝐶𝑂2𝑒 emissions per 𝑀𝐽 of CJF increase from 89 to 257.2 [192.3-334.9] 𝑔𝐶𝑂2𝑒/𝑀𝐽. Similarly, for all paraffinic CORSIA eligible SAFs [3], the 𝐶𝑂2𝑒 emissions per 𝑀𝐽 increase by 147.7 [88.4-223.3] 𝑔𝐶𝑂2𝑒/𝑀𝐽. The values in the brackets indicate a 5%-95% confidence interval range based on a Monte Carlo uncertainty analysis with 1000 simulations.
• As aresult of the previous point, a hypothetical SAF that is able to reduce lifecycle GHG emissions by 100% (with 0 WtP emissions), only has a climate impact reduction of 42.5% [33.5%-54.1%] when using ATR100, and58%[53.3%-66.7%]when using GWP100 as the climate metric. Nevertheless, the absolute WtW reduction in climate impact increases from 89 𝑔𝐶𝑂2𝑒/𝑀𝐽 to 109.5 [99.2-118.3] 𝑔𝐶𝑂2𝑒/𝑀𝐽 (using ATR100), meaning that SAF’s climate impact reduction potential actually increases when PtW non-𝐶𝑂2 effects are included. This is explained by the fact that SAF not only reduces 𝐶𝑂2 emissions, but also contrail climate impact, which strongly outweighs the increase in SAF’s 𝐻2𝑂 climate impact.
• When adding the CORSIA default WtP values [3] to the PtW values derived in this analysis, SAF’s climate impact reduction potential ranges from 3% or 8.9 𝑔𝐶𝑂2𝑒/𝑀𝐽 (for corn grain EtJ) to 47% or 121.1 𝑔𝐶𝑂2𝑒/𝑀𝐽 (for Herbaceous Energy Crops-FT)- depending on the exact feedstock and conversion process used.

A sensitivity analysis has been carried out for the PtW analysis from which it was concluded that the PtW climate impact of both SAF & CJF strongly varied. However, the absolute WtW climate impact reduction potential stayed very similar: the lifecycle 𝐶𝑂2 climate impact reduction remained unaffected, and the PtW non-𝐶𝑂2 climate impact reduction potential varied from 11.75-24.4 𝑔𝐶𝑂2𝑒/𝑀𝐽. Lastly, by allocating SAF to longer flights with higher average flight altitudes, SAF’s non-𝐶𝑂2 climate impact reduction potential is substantially increased from 4.06 to 25.6 𝑔𝐶𝑂2𝑒/𝑀𝐽.