Adding an EGR system will make soot worse, not better.

The role that diesel smoke plays in air quality is not clear cut. Old diesels with low pressure injection systems produced much more soot by mass. However, the visible soot particles are large and fall out of the atmosphere after a few minutes.

High pressure injection produces much less soot by mass but a much higher number of soot particles. These particles can remain in the atmosphere for a week or more until they become large enough to fall out of the atmosphere.

Of course, this subtlety is lost on the poltical ignoramuses who decide that 'something must be done!' and don't let ignorance get in the way of creating new rules.

They are a possible carncinogen. My point is that you might actually have a worse particulate problem with a modern diesel than with an old one, even though on paper at least, the new one looks a lot cleaner.

Particulate emissions are only based on mass and not number-even though the number of particles is arguably more important.

In any case DPF drastically reduces soot mass and number!

Quite.

since mass scales to the cube of radius, it is quite possible to reduce the total mass of soot emitted, even if the total number of particles increases dramatically. This is exactly what has happened.