We study contrail formation behind future fuel cell-based aircraft fueled by hydrogen. Simulations show that, under certain conditions, small droplets can form via a process not occurring in current plumes. This can increase ice crystal numbers in contrails, boosting their climate impact. The effect is strongest in cold air and for high plume mixing rates with air. We suggest to decrease the mixing rate and exhaust humidity by technical design to reduce the climate impact of such aircraft.

In this work, we share the results of first in-flight emission and contrail measurements behind a fuel cell exhaust emulator, with the goal of quantifying the contrail properties for this new aviation propulsion concept. An artificial dilution tracer system was used to assess plume dilution and derive emission indices. At ambient temperatures close to the homogeneous freezing threshold, a strong temperature-dependence of the number of contrail ice crystals, due to droplet freezing, was observed.

We develop an easy-to-use tool to estimate the per-flight climate effect of CO₂ and non-CO₂ emissions, based only on aircraft size as well as origin and destination airports. The implemented model results from a comparison of Multiple and Symbolic Regression approaches and exhibits a mean relative error of 21 % with respect to climate response model results. The simplified method is designed for climate footprint assessment and covers jet-powered passenger aircraft with over 20 seats.

The study introduces a novel parameterization for the number of contrail ice crystals formed on ambient aerosols entrained into the exhaust plume behind aircraft burning hydrogen. This parameterization can be integrated into large-scale models to assess the radiative impacts of contrails originating from a fleet of aircraft with hydrogen combustion.

We provide observations of the geostationary Meteosat satellite with contrails labeled by three people complemented with detailed cloud information. Contrails influence climate but are hard to identify in satellite imagery. With this study, we support contrail detection development and evaluation, stress the subjectivity of human labeling and reveal which meteorological conditions highlight or hide contrails. This dataset contributes to a better understanding of aviation’s climate impact.