Carbon Dioxide is what you breath out hense CO2 the two means Di and Di means to resulting in DIoxide. Monoxide is exhause and will kill you and it would be CO. Iv Taken AP Chem And AP Bio and scored 5's on both finals i know whats going on here

 

this is very pointless since his question was answered and no one was asking the difference. So you took AP chem. I had Advanced Chem in college, that doesnt make me an expert on it. And obviously thats what the terms mean. I just figured he was asking about CO because that is generally what is testing for cars, but there also is a CO2 emmision that EPA has been starting to be weery of because of the whole global warming issue