"And your understanding about diesels is very poor. The "complexity" of engine controls is true for all modern vehicles, emissions or not. And no. No. No. Diesels normally run less than the allowed emissions, less CO2 than gasoline cars, and some electric cars that use coal powerplants to recharge."[/QUOTE]
Yes, Diesels are more efficient than gasoline engines because Diesels burn fuel at much higher temperatures, extracting more energy. Inherently, then, Diesels generate less CO2 per mile. But, these higher temperatures are what cause a higher percentage of nitrogen to combine with oxygen to form oxides of nitrogen, or NOX (typically NO or NO2). To cool the combustion slightly, exhaust gas is recirculated into the combustion chamber to dilute the O2 in the intake airstream; this EGR valve is controlled based on load demand. (EGR was probably also reduced during the VW cheat in order to boost performance). After leaving the engine, Diesel exhaust goes through a very complex set of after treatment devices, as show in this video link from VW:
VW Touareg TDI and Audi Q7 Adblue emissions explained - YouTube
A number of these sub-system are not present in a gasoline engine after treatment system, including the Diesel particulate trap, urea tank, urea injector and a Diesel exhaust deNOX catalyzer. It is not easy to clean up any engine; Diesels are tougher.
Yes, I understand that Europeans have been more focused on CO2 than some of the other emissions, but they now realize they are paying a price. Diesels are polluting their cities with a particularly nasty set of pollutants, including fine particulates not present in gasoline engines. For those of us in Los Angeles, knocking down NOX was the key to cleaning up our air, and it has worked!
In January, 2016, VW produced an excellent - albeit defensive - video on how emissions are controlled on a Diesel and also tells how they cheated.
How Do Modern Diesel Engines Work? VW Explains It On Video
BTW: I was told that even in a well-controlled Diesel with urea injection (often referred to in the trade as panther piss!) a small amount of ammonia into the atmosphere. But because no one every imagined spraying urea into the exhaust system back when emission standards were written, ammonia (and other stuff) is not a controlled pollutant.
The VW cheat answers the question we engineers have had for over a decade: how the hell does VW do it?!
Sadly, other companies will probably also be caught cheating....in part driven by a demand on the company's engineers that "If VW can do it, then so can we!"