The increased Nitrogen oxides in internal combustion is due to the compression phase of these motors. Given enough heat and pressure the Nitrogen from the atmosphere can be involved in more chemical reactions. Usually Nitrogen doesn't want to react much but we are forcing it to. This is why Diesel engines with higher compression ratios produce more Nitrogen oxides. As for CO that is more to do with incomplete combustion and is getting less and less with better engines running lean fuel mixtures and more computer control. In theory the Catalytic converter should be reacting most of the CO into CO2 but it's not going to be 100%.