In Europe, for about 10 years we have had a series of legal restrictions on what diesle engined can emit, called Euro 1, Euro 2, etc.
From Euro 4, these have been met by running the engine very hot, which creates masses of oxides of Nitrogen, and then neutralising the NOx by squirting ammonia into the exhaust pipe. his works fine in a laboratory environment. Unfortunately, a truck can go from buring 20 ccs of fuel per hour to burning 2 litres a second* in two turns of the crank shaft, and there's not a bat's chance in hell of getting the ammonia to match the NOx during the transition. These engines produce very fine particulates that can go strait through the skin - and enter the blood through the lungs very easily. Real life pollution is very bad. Unfortunately, the option of running the engines cooler and filtering out the lumps of carbon mechanically, was ruled out, because the people selling the Ammonia (pig's piss, sold as "Ad-Blue") paid vast bribes to the European comissioners. MAN Diesel demonstrated an engine that could do this but did not put it into production "for commercial reasons".
Manging the supply of, and carrying expensive 5% Ammonia solution around with them is something truck owners and drivers would go a long way to avoid - though whether that goes as far as buying auto-transmission trucks (which is MAN's product) is another question. They are really difficult to reverse into a loading bay with potholes near where the rear axles come to rest (ie most loading bays). We are talking up to FIVE rear axles here.
* Think: reaches bottom of hill in fully loaded 44 ton truck at just over 56MPH (truck speed limit for Europe) and stamps on the throttle pedal of a 16 litre turbo-charged engine as he hits the incline of the upward hill.