You can see why dpf’s Egr and ad blue are used. If you go out in something and watch nox levels before and after the cat on something like a euro 6 engine it gets the levels down to fook all. Far to complicated now though. Like the latest euro 6 stuff. As they have to meet emissions levels right from start up un like euro 5. The newest daf trucks have egr to resurculate exhaust gases and help get the engine up to temp as quickly as possible so the after treatment system can take over. Things are getting far to complicated these days lol