Contrail formation and persistence conditions for alternative fuels

In order to counteract global warming, the European Green Deal was made to improve the journey to a sustainable future. This also has an impact on aviation, because in the future the growth in air traffic must no longer lead to rising emissions, but even all aviation CO2 emissions have to be reduced to zero to achieve the goal of climate-neutral aviation by 2050. There are several approaches for new propulsion solutions and sustainable vehicle configurations and operations. A promising approach is the use of modern fuels. These include drop-in fuels (kerosene-like fuels) but also revolutionary concepts such as the use of liquid hydrogen or of liquid natural gas, electric flying, and mixed forms of these. These approaches have certain advantages regarding the climate impact, but not all processes and effects are fully understood, especially their effects on contrails and their properties, frequency, and lifetime. In this study, we analyse 10 years of airborne and reanalysis data of temperature and humidity to see, how much more persistent contrails would be formed if kerosene were replaced by alternative fuels of different energy-specific water vapour emission indices, which are generally higher for alternative fuels. It turns out, that the amount of additional persistent contrails is quite minor for drop-in fuels, which are already used nowadays, but it is larger for another kind of fuels, such as methane and liquid hydrogen.