Volkswagen, microprocessor scams, and NOx

The great Volkswagen emissions scam is breaking big.  They canned the CEO of Volkswagen yesterday over the matter.  Apparently, the microprocessor in the diesel VW's was able to sense when the car was undergoing an EPA emissions test and adjust something to make the engine run cleaner.  Sensing when the car is being tested isn't all that hard, if the engine is revving up above idle but the car isn't moving, it's on a test stand getting tested.  The anti skid sensors on each wheel will let the microprocessor know if the wheel is turning.  Unless all four wheels are turning, the car isn't moving and it doesn't take great programming skill to make a few adjustments to engine operation. 
   Just what the microprocessor can do on a diesel is less clear to me.  Diesels don't have ignition systems (spark plugs) so there is no ignition timing to fiddle with.  There is the fuel air mixture, I suppose setting the mixture extra lean will spoil the combustion, lower combustion temperatures, which reduces the "NOx" emissions.  It also ruins fuel economy and power output.  In engines, running hotter give you more power and better fuel mileage. 
  It could be the problem is the US standards for nitrogen oxide ("NOx") emissions.  The air is 80% nitrogen and 20% oxygen.  Heat air up enough and the nitrogen and oxygen go together in various combinations, NO2, N2O4, etc.  The temperature inside the cylinders of an engine as hot enough to form "NOx".  The is the basis of the famous Haber process for making "fixed nitrogen" for fertilizer and explosives.  Plants need fixed nitrogen, ("NOx") and cannot make it them selves.  Another fact from freshman chemistry, All nitrates are soluble.  Which means all the "NOx" in the air will come down in the rain and fertilize the fields.
   So why is "NOx" called a pollutant?  Partly because the EPA likes to call as much stuff pollutants as it can because it gives them more areas to throw their weight around.  In the case of "NOx" the source of LA smog was found to be a combination of "NOx" and oily hydrocarbon vapors, unburned gasoline.  Under the impulse of sunlight the two chemicals will combine and make smog.  The correct solution would have been to clamp down on unburned hydrocarbons, all sources of which represent poor engine performance or leaks and spills.  Without any unburned hydrocarbons, you can have all the NOx in the air you want and not get smog.  
   Well, the EPA didn't do that, they are off on a "NOx" kick, have been for 40 years.  And it hurts.  Diesel is more efficent that spark ignition engines.  In Europe half the automobile fleet is diesel. In the US nobody drives a diesel.  Reason?  US "NOx" standards are much tighter than they are in Europe.  Apparently the only way to get a diesel car to pass US emissions tests was to cheat, which is apparently Volkswagen's solution to the problem.
   It's time to have a public debate on "NOx" standards.