Modeling the impact of aviation fuel hydrogen and sulfur content on contrail properties: insights and implications

Contrail cirrus represents the most significant warming component within the total aviation impact on climate, suspected to exceed even the effects of aviation CO2 emissions. It remains to be shown that regulating hydrogen and sulfur content in aviation kerosene could help to reduce the climate impact from CO2 and from contrails, in order to allow for a science-based jet fuel standardization. Hence, this study conducts a model-based scenario analysis of the climate impact of the European fleet in 2019, exploring different levels of aromatic and sulfur reductions in fossil fuel-based kerosene as short-term mitigation measures.

Using the Lagrangian plume model CoCiP within the open-source pycontrails package, we simulate contrail properties and energy forcing (EF) for a reference fleet using Jet-A1 fuel (13.8% hydrogen content) over Europe in 2019. For scenarios with increased hydrogen content (13.8%–15.4%, in 0.2% increments), reductions in non-volatile particulate matter (nvPM) emissions and changes in contrail properties—such as initial ice particle number, persistent contrail formation, age, optical depth, contrail coverage, and EF—are quantified. In parallel, sulfur content scenarios—including high and ultralow levels with increased and reduced soot activation fractions, as well as zero sulfur—are analyzed, to estimate the impact of sulfur-mediated elevated or reduced activation of aerosol into water droplets.

The reference simulations compare well to previous studies. Furthermore, results show that increasing hydrogen content from 13.8% to 15.2% (the theoretical maximum) enhances the potential for persistent contrail formation from 13% by 6%, but reduces nvPM emission index from 1.22 x 10¹⁵ kg^-1 by 61%, contrail age from 2.37 h by 20%, contrail optical depth from 0.12 by 24%, and contrail cirrus coverage from 0.67% by 34%. This leads to a reduction in total EF by up to by 52%. The high sulfur scenario increases contrail EF by up to 10%, while the ultralow scenario reduces EF by up to 14%. The simulation of the zero-sulfur content scenario represents the potential lower limit and serves as a pre-study for hydrogen combustion. These findings, part of the European Fuel Standard project by the European Union Aviation Safety Agency, demonstrate how improving fuel composition can mitigate aviation climate impact. These results  highlight the potential of hydroprocessed and ultra-low sulfur kerosene as near-term solutions, providing actionable insights and implications for the development of aviation fuel standardization.