The limit values for harmful emissions are becoming ever stricter. The ability to comply with these values requires not only fuel combustion that is as clean as possible but also a process of exhaust gas treatment. The nitrogen oxide emissions of a modern diesel are now 96% lower than those of a typical diesel from 1990. The SCR catalytic converter (Selective Catalytic Reduction) and Denoxtronic from Bosch further reduce the remaining nitrogen by more than 90%. It therefore comes as no surprise that, in some cities, the cleaned exhaust gases are cleaner than the ambient air.