"While I know that I am not aware of every possible component and strategy that makes up an emission control system in a gasoline engine, I know that generally, the four primary emissions control hardware components are the exhaust oxygen sensor, the catalytic converter, the charcoal canister and the engine control module (ECM). The ECM controls the air/fuel mixture to a desired value, usually right around the stoichiometric ratio for gasoline, based on feedback from the exhaust oxygen sensor. The catalytic converter actually does the bulk of the work in converting carbon monoxide (CO), hydrocarbons (HCs) and various nitrogen oxides (NOx) into water, carbon dioxide and nitrogen gas. It does this by providing a large surface area for catalyzing these reactions using precious metals like platinum, palladium, and rhodium. The reason maintaining an air/fuel ratio near stoichiometry is so important is that CO and HCs require oxygen for their reactions, so their conversion is most efficient when there is more air than fuel, while NOx is converted better in a rich environment. The best mutual efficiency is near stoichiometry.

To be completely transparent, I don't know that much about how a charcoal canister works. I know it is supposed to trap fuel vapor instead of letting it directly out into the atmosphere, but I am not completely aware of the details of what happens next. Obviously, the trapped gasoline vapor has to go somewhere, or it would eventually be released or cause the canister to blow up. So it must get routed to the engine at some point. After all, it's just gasoline, so why not? But I admit that I would have a lot to learn about the evaporative emissions system."