Brain fart - Nitrogen enriched fuel and smog

I have noticed that local Shell Oil stations are touting a new fuel additive. They have signs up all over the place talking about their New Nitrogen Enriched Gasolines:

Shell Launches New Nitrogen Enriched Gasolines
02/03/2009

Today at Shell stations across the U.S., consumers will fill-up with a new product at the pumps. Shell is introducing the all-new Nitrogen Enriched Gasolines, containing a unique, patented cleaning system designed to seek and destroy engine �gunk� (carbon deposits) in all three grades of gasoline. The new Nitrogen Enriched cleaning system protects and cleans up gunky build-up on intake valves and fuel injectors left by lower quality gasolines.

Nitrogen is a key element of the active cleaning molecule in the new fuel, making it significantly more stable at higher temperatures common in modern engines, such as direct fuel-injection gasoline engines. The increased stability ensures that the molecule can work under much tougher engine conditions by resisting thermal breakdown better than conventional cleaning additives.

So these are for cleaning and not preventing buildup in the first place. That means that the combustion byproducts will join all the rest of the stuff in the exhaust. What got me thinking is that various Nitrogen Oxides are a prime constituent in Smog. I'm sure the chemistry is well worked out but still...