Are you certain about that? I know a car emits much more CO2 and H2O than most anything else, but as an example, I was pretty sure the smog over L.A. was a direct result of oxides of nitrogen. Or was that only toxic, and not greenhouse, and thus not part of our consideration?
According to http://www.epa.gov/oms/climate/420f05004.htm cars also produce significant amounts of methane and nitrous oxide, which are both greenhouse gases. However good old CO2 represents 94-95 percent of the greenhouse potential from your average car.
So no, it is not all CO2, but the rest is a rounding error.
Nitrogen oxides are both toxic and greenhouse gases, but in the quantities that they're emitted from tailpipes, the toxicity is a much bigger problem than the greenhouse effect.
