The whole thing is barking
If it's genuinely about emissions and air quality and not simply a way of grabbing money then surely if a vehicle is too "dirty" then it shouldn't be allowed into the zone. End of.
Maybe they should factor in the environmental impact of the mineral & oil extraction/refining/building/painting etc.etc. of new vehicles.........
Andy.
PS Has anyone charged Trump's entourage and helicopters? Just seen a great plume of stuff coming out of the aerial support......