As fleets work towards reducing emissions, understanding the differences in aftertreatment systems for various fuel types is crucial. The adoption and growth of hydrogen internal combustion engines (ICE) is a significant step as hydrogen ICE provides a low-emission, low-carbon option for a more sustainable transportation sector. The mechanisms that clean exhaust gases in these engines are fundamentally the same as diesel ICE, with the key difference being what is in the exhaust gas to start with.