TTW CO₂ emissions will be zero for hydrogen but the carbon content of the pilot fuel will result in a small amount oof emissions. The actual value will depend on engine load, pilot fuel quantity and pilot fuel type.

WTW CO₂ emissions will depend on the source of the hydrogen. Grey hydrogen will actually increase the carbon footprint when compared to diesel. Green hydrogen will dramatically reduce the carbon footprint but the difficulties of producing green hydrogen at scale have already been mentioned.

SO_x emissions will be very low and only due to the pilot fuel component of the fuel.

NO_x emissions will, as always, be a function of the combustion temperature and the duration of that high temperature. The combustion temperature will be higher when burning hydrogen which will lead to higher NO_x emissions. The exact level of emissions will depend on whether a high, medium or slow speed engine is employed.

PM emissions will be lower than with diesel or heavy fuel oil as the only carbon-carbon bonds will be in the pilot fuel.