For those not reading closely note that Hydrocarbons != Carbon. A New vehicle will burn fairly completely (if you include the cat as part of the process), leaving a miniscule amount of hydrocarbons (incompletely burned fuel) and a small amount of CO. The catalytic converter will oxidize hydrocarbons, CO and NO2 leaving almost entirely N2 CO2 and H2O (and in fuels with significant sulfer, hydrogen sulfide which has its own issues).