If I may add that measuring HC, CO, CO2 and O2 merely indicates the combustion quality of the diesel engine operation, and with EGR it is expected that NOx should go down, however, NH3 injection amount is critical to minimize NH3 slippage from the exhaust. One needs to quantify the amount of NH3 slipped in the exhaust at different exhaust gas temperatures (depending on the driving and load conditions) which in-turn assists in estimating NH3 consumption, on-board NH3/Urea storage etc. during a cycle-run.
Your product will be greatly benefited if you can incorporate NH3 measuring sensor which would be resilient to the presence of H2O. In my humble opinion, NH3 injection amounts should not be same/constant at different driving/operating conditions, and without actually being able to measure NH3 on-board or by means of an analyzer, we are missing a critical information.
I hope this helps your developing team. All the best!