The question is whether the current discussion does not get stuck in the middle (or at the beginning). To this, a small current note from BMW, where certain M-models are now again equipped with cardan shafts made of steel instead of composites to create space for a particulate filter. So one would have to include modern petrol engines in the discussion on fine dust.

The SCR installation is rightly the key to solving nitrogen oxide problems. These are known in μg/m³. The retrofit solution can not fully cope with a SCR system controlled by the engine management system, which runs the diesel leaner in favor of more NO_X emissions and thus reduces particulates and CO₂. In addition, heating by more fuel is more favorable than via the vehicle electrical system, as with the retrofit solution does.

But you can not have it all. The production of a new car is not environment compatible and much more expensive. The environment is spared by the retrofit solution, too. But the particles are getting smaller in the injection technology with significantly higher pressures and more parts injections getting. The limit values already include PM_2.5 with a diameter less than 0.1 µm (1/10,000 mm).

But questions remain open. Do not damage the ever-decreasing particles because they may be more likely to get e.g. into the lungs? Are these really quite completely burned in SCR systems without particle filters? Can these be trapped or burned when the particulate filter has just been regenerated, or only when it is filled or never?