Better and Cleaner are 2 different things; No matter what, an ICE is going to output CO2 and H20; and depending on the fuel a few extra Cs. CO2 or H2O concentr

Better and Cleaner are 2 different things; No matter what, an ICE is going to output CO2 and H20; and depending on the fuel a few extra Cs. CO2 or H2O concentrations are enough to make things worse for an engine or a human, but are not necessarily dirty. NOX and CHs however are not as "naturally" in the air and producing them definitely makes the air "dirtier"