The impact of Stratospheric Aerosol Injection and other geo-engineering scenarios on aircraft plume chemistry and contrails from conventional and alternative fuels

Aircraft emissions play a role in human induced climate change, in particular condensation trails (contrails) formation, NO_x and CO₂ emissions. Recent years have seen increased research output in contrail studies and mitigation. Geo-engineering has gained attention in recent decades, with the objective to increase the global albedo resulting in reduced radiative forcing. Scenarios for geo-engineering include stratospheric aerosol injection (SAI), Marine Cloud Brightening (MCB), silver iodide injection as well as more niche scenarios. The interaction between aviation and geo-engineering remains underexplored. We explore the role of geo-engineering on contrail formation, persistence and aircraft plume chemistry employing the Aircraft Plume Chemistry, Emissions, and Microphysics Model (APCEMM). We apply this to jet fuel A-1 as well as potential alternative fuels with respective emission indices’ parameters including Synthetic aviation fuels (SAFs), hydrogen internal combustion jet engines and ammonia. We evaluate the chemistry background composition using theoretical adjustments and the G6-Sulfur experiment in CMIP6 model outputs. We explore how the result of increased particulate matter from increased aerosol number density, resulting from geo-engineering, facilitate the seeding of contrail formation. We find changes in ice crystal number density, heterogenous reaction rates of nitric acid, ozone perturbations optical depth of contrails, contrail lifetimes and total extinction, providing insights into the radiative forcings from SAI influenced contrails. [An increase in ice crystal number density is observed due to an abundance of sulfate aerosols acting as condensation nuclei. Reductions in the efficacy of alternative fuels such as hydrogen at minimising contrails, both in lifetime and forcing, when background aerosols replace soot as nucleating particles. Enhanced heterogonous reaction rate were found to increase HNO₃ with SAI by 5 % for a 50 % increase in SO₂ ]