This page deals with everything that is related to exhaust emissions or exhaust emission control.
Links:
a Toyota paper on emissions, combustion chemistry and related topics [part#1] [part#2]
Tobias: Makes me wonder: How about we devise an exhaust gas Voltammetry System to analyze the composition on the fly?
I suspect that's what the Exhaust sensor at the Smog Check is!?
http://www.transportation.anl.gov/sensors/microsensor.html
http://www.princetonappliedresearch.com/applications/sensor/main.htm