Influence of Reduced Soot Emission and Increased Water Vapor Content on Contrail Climate Impact

Abstract

Contrails have a significant impact on climate and contribute to global warming. Their formation is primarily caused by the emission of water vapor and soot particles from aircraft engines. When water vapor is released into the cold and humid upper atmosphere, it can rapidly condensate on soot particles and form ice crystals. Reducing carbon and soot emissions from aviation is critical in mitigating the climate impact of air travel. Hydrogen presents a compelling alternative to traditional jet fuels; it emits no carbon when burned in an engine, although it does produce more water vapor, which could intensify contrail formation. In our study, we explore the effect of reducing soot emissions and increasing water vapor in the engine exhaust as a first step towards using hydrogen as fuel. The Contrail Cirrus Prediction (CoCiP) model was used to simulate contrail properties and estimate their climate impact. We focus on Europe with air traffic data from Eurocontrol for the entire year 2019. Specific aircraft data were obtained from the BADA3 database, soot emissions stem from a state-of-the-art method to scale ICAO emissions to cruise conditions and weather data from ECMWF-IFS forecast. For our investigations we reduce the engine soot emissions for kerosene by up to 99% for the complete fleet. Then for each flight and aircraft, we calculate the optical thickness and radiative forcing from contrails in Europe in 2019 based on ECMWF weather information and quantify the relative changes for a stepwise reduction in soot emissions of the fleet. In a second step we increase the water vapor emissions in relation to the expected change for future hydrogen combustion. Results from the simulations are presented and the potential impact for future novel engine technologies and fuels are discussed.