## 1 _Applied_
### _Sciences_
* **Operational measures on-ground** being implemented at the airport both air- and landslide including, for instance, the upgrade of existing airport infrastructure according to energy-efficiency criteria [34], sustainable taxi operations, e.g., by switching to single-engine, electric, or hybrid solutions [21; 35; 36], electrification of ground vehicles [37; 38], or producing renewable energy at airports [39]. Typically, the results from different individual studies in terms of climate mitigation potentials are not directly comparable to each other. This is due to different definitions of the reference system used in the modeling process regarding spatial and temporal scope, considered fleet and airports, incorporated missions and atmospheric boundary conditions as well as varying modeling assumptions. However, a direct comparison is required to identify the most effective mitigation measures, to support their implementation, and to realize their potential to reduce the climate impact of aviation. The development of adequate regulations and policies to implement such mitigation measures and to achieve the defined climate goals also calls for a comparative assessment of the different mitigation approaches. Furthermore, an efficiency assessment of the different measures combining ecological and economic consequences is required from an operator's perspective for a reasonable implementation. While previous studies have already presented a detailed quantitative comparison of two operational measures based on similar boundary conditions and modeling assumptions, e.g., [16; 25], analyses including several mitigation approaches have typically focused on a sole qualitative comparison of measures so far, e.g., [10; 40; 41]. Further work of research has looked at possible mitigation scenarios and pathways aggregating different mitigation measures but lacks a direct comparison of individual improvement means, e.g., [8; 42]. This study presents a comparison of different operational measures to reduce the climate impact of aviation. Our goal is to identify especially effective and efficient approaches from a set of in-flight and ground-related improvements. We contribute to the current state of research, first, by summarizing mitigation potentials of different measures in a comparable way, second, by providing a comparative method to scale obtained results from individual measures to one common reference and, finally, by comparing different promising measures regarding their effectiveness and efficiency to mitigate the climate impact of aviation also considering the effects on the aviation stakeholders. For this purpose, the paper is organized as follows: Subsequent to this introduction (Section 1), we explain the applied methodology for comparing the different measures and describe the method application for different types of improvements in Section 2. The achieved results are presented in Section 3, before these are discussed with regards to comparability, the underlying uncertainties, and the measures' applicability (Section 4). Section 5 summarizes the results and concludes with an outlook on further research. This work is part of the EU Horizon 2020 Project on 'Climate assessment of innovative mitigation strategies towards operational improvements in aviation (ClimOP)', which aims to define promising mitigation strategies and regulatory recommendations based on a comprehensive climate assessment of different operational measures in aviation. In this context, both in-flight and on-ground operational measures are investigated and compared considering implementation on a European scale.