Hydrogen Hydrogen fuel cell buses convert gaseous hydrogen into electricity through an electrochemical reaction, emitting only water vapour from the tailpipe, which can be collected for later use. One of their principal advantages lies in operational autonomy: hydrogen vehicles typically achieve ranges of 350 to 500 km on a single refuelling, which is particularly advantageous in large airports with extended apron networks (where buses are specialized vehicles used to transport passengers between terminals and aircraft) or where buses operate on multi-shift cycles with minimal downtime. Moreover, hydrogen systems can deliver consistent power output regardless of ambient temperature, allowing auxiliary systems such as air conditioning or cabin heating to operate without significantly compromising range – an important consideration in airports located in extreme climates or where passenger comfort requirements are stringent. Refuelling is rapid, often under 15 minutes, enabling high vehicle availability and reducing the need for large spare fleets. Operationally, hydrogen buses are particularly suited to airside use cases where flexibility, long duty cycles and reduced turnaround times are critical, and where land availability allows for the installation of a dedicated hydrogen refuelling facility. For instance, Greater Toronto Airports Authority’s plan for hydrogen bus adoption is strongly linked with the airport’s wider ecosystem,9 benefiting from the installation of a hydrogen refuelling station outside of airport boundaries for light and heavy-duty vehicles.Retrofitted buses Retrofitted diesel buses offer a transitional decarbonization pathway by replacing the internal combustion engine and associated components with alternative powertrain solutions – most commonly full battery-electric, but potentially also hydrogen ICE, or hybrid systems that combine combustion and electric drivetrains (including plug-in variants). For the purposes of this analysis, however, only the conversion from diesel to full battery-electric is examined in detail. This intermediate solution is particularly interesting for airports with a relatively new bus fleet (fossil- fuel or biofuel based). This allows them to extend the operational life of their fleets while achieving substantial reduction in tailpipe emissions, avoiding the capital cost of procuring entirely new vehicles (a retrofitted bus could cost significantly less than the price of a brand-new electric one). From a technical standpoint, retrofitting can be completed in a fraction of the time required for full fleet replacement, and it enables the reuse of bus bodies and chassis and leaves the interiors in serviceable condition. The main opportunities lie in legacy fleet decarbonization where budget constraints, long procurement cycles or sustainability targets demand rapid emissions reduction. However, retrofitting presents challenges: the diversity of existing fleet specifications can complicate conversion processes, certification requirements may vary by jurisdiction, and maintenance teams could require retraining to manage the new systems. Decarbonizing Aviation Ground Operations: Alternative Bus Technologies 10

Decarbonizing Aviation Ground Operations 2025