Turbo Diesel Exhaust ?

[Gregory891]

Interesting, this has the diesel catalyzer (build list from BMW Archives as well as BMW ETK on realoem). It didn't have the optional factory installed DPF (S200A). As your car was a UK delivery, and UK emissions based road tax bands were based on CO2 (fuel consumption) with no particulate (PM) requirement, there was no incentive be extra clean in PM sooner than EU emissions standards.

Conversely in Germany, an emissions based road tax did exist at the time which additionally looked at PM - so you would see some cars with the factory DPF option to lower the annual road tax. Retrofit DPF's were driven in Germany with the pollution sticker system (which started in 2008), so many E53 diesel that would still be on the road in Germany today would have been retrofit with a DPF. The consequence of not doing so: much higher annual road tax and a yellow emissions sticker - which means that today, you can't drive in any medium to large size city.

Switzerland did this (half price annual road tax for DPF retrofit) in specific cantons for a time, but this has now ceased as the overall car fleet has modernized since then.

It would be interesting to know what (if any) advantage or requirement is mandated in AUS or NZ.

My experience with the DPF is positive, the car doesn't have the same order at idle nor when you switch off after a drive. Drive-ability and noise are no different.
It passed the (biannual) pollution tax previously but the cat needed to be quite hot, now it's easier to recheck and PM levels are lower.