Contrail formation is one the largest warming contributions of aviation’s climate impact. Measures to mitigate contrail climate impact include the optimisation of flight trajectories to avoid the formation of warming contrails or to find air space where extra cooling contrails are formed. The latter option is only possible during daytime, due to the interaction of a contrail with the short-wave radiation from the Sun. Little research is done to evaluate the effect of the diurnal cycle on contrail climate impact mitigation. Moreover, models to predict this the contrail climate impact are still in the development face. This thesis aims to (1) find the daytime and nighttime contrail climate impact of eco-efficient flight trajectories, (2) to assess the prediction’s robustness and (3) to recommend a best practice for eco-efficient flying by using the difference between the daytime and nighttime contrail climate impact. To this end, simulations were carried out within the EMAC climate chemistry model, aided by the submodels AirTraf, CONTRAIL and ACCF. The robustness of the results were tested against a model parameter: the threshold time until sunrise (THsunrise). When a contrail is formed
during nighttime, THsunrise determines whether the contrail is formed sufficiently close to sunrise to be considered a daytime contrail. It is concluded that winter daytime mitigation of contrail climate impact is more eco-efficient than winter nighttime mitigation. Overall, daytime mitigation achieves a larger maximum reduction of contrail climate impact than nighttime mitigation. moreover, summer mitigation is more effective than winter mitigation and winter
mitigation has a larger reliance on the formation of extra cooling contrails. The thesis results are robust with respect to a varying THsunrise. However, overall results become biased to daytime results or nighttime results. Lastly, it is shown that differences between day and night contrail climate impact mitigation allow for the enhancement of mitigation results.