## Appendix A.3.1 Assessment Approach  
Each of the selected OIs follows an individual assessment approach to obtain changes in fuel and energy consumption as well as emission quantities due to their specific characteristics, before the resulting climate effect is quantified.  
For the assessment of SETX, we model the emissions on the basis of engine information and taxi times, as compared to the energy needed for towing vehicles for selected representative aircraft types (E190, A320, B738, and A350). Engine emission indices are derived from ICAO engine emissions data bank [86], while taxi-in and taxi-out times are based on recorded times for a representative selection of aircraft types on a peak day [93]. Engine warm-up and cool-down times are assumed to be 3 and 4 min. Potential fuel and resulting emission reductions are calculated considering measured taxiing times, engine-preparation times, and average fuel consumption rate for the engine in idle. The corresponding energy demand to power a fleet of electric tow trucks is calculated accordingly. Based on the assumption that approximately 80% of the values of fuel consumption and energy demand (and corresponding GHG emissions) of a peak day are representative of an average day of operations, results are extrapolated to the entire reference year 2018. The economic assessment is based on the initial investment per tow truck considering the optimal number of tow trucks at the selected airport [49; 50].  
To quantify the effects of ELEC, ground vehicles are classified regarding vehicle size (small-, medium-, and large-sized) and traction (petrol, diesel, and electric). The corresponding emissions are estimated as well as the emissions from the assumed European mix of electrical energy sources to fuel the electric vehicles. On this basis, emissions from petrol and diesel vehicles can be compared to their electric equivalent. Consequently, results are used to calculate the overall savings for any vehicle fleet. Based on the detailed available data at MXP on the actual ground fleet composition and average daily mileage of each vehicle, results from the OIs implementation in terms of fuel and energy consumption can be compared to the BAU reference case [49].  
The assessment of INFR is performed with the EnergyPlus model (The open-source software developed by the US Department of Energy, [[https://energyplus.net](https://energyplus.net)]([https://energyplus.net](https://energyplus.net)), accessed on 2 March 2023), and focuses on the reduction of CO\({}_{2}\) emissions of a conceptual office building due to the application of the selected energy-efficiency measures mentioned above. In this course, different climate zones according to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) classification of the geographical distribution of climate conditions are utilized to model the energy consumption of the conceptual office building at different locations. Results obtained for one conceptual office building are then scaled to the total energy consumption at the airport level through a proxy calculated as a logarithmic function of the number of aircraft movements [49; 51].  
Finally, the climate impact assessment for all three considered OIs is performed based on the obtained emission quantities and converted into ATR following Sausen and Schumann [69].