I assume CO2 is only a portion of the exhaust. Not sure if that’s what you were meaning already?

Edit: No idea of the quality of this source, but:

So what’s coming out of a car exhaust is 13 per cent CO2, 13 per cent water (26 per cent sub-total) and 73 per cent nitrogen gas. The air that you’re breathing right now is 78 per cent nitrogen gas, 21 per cent oxygen, and one percent everything else.