What about O2(a by-product of electrolysis when producing hydrogen for fuel)? Do you consider that to be pollution too?
Pollution emerges when something is left outside a closed ecological cycle. O2 is released at the electrolysis process, but it's consumed in a H2 burning process. So we have a cycle: 2H20 (electrolysis)-->2H2+O2-->2H2O (burning). If we have an alike cycle producing energy for the electrolysis, we have an unchanging (non being polluted environment). If we look at the conventional combustion engine, the same cycle can be maintained if we can convert the CO2 and H20 produced at combustion into oil (or petrol).
Continuation: so the O2 from electrolysis isn’t a polluting agent. CO2 from our caloric engines is a different issue, since it’s not balanced with th O2 generation done by the plants.