Comment by JorgeGT

I research for the auto industry and this was very well known by the authorities. Fixed test cycles like the New European Driving Cycle https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Ne... were easy to detect, and easy to optimize against. That's why coming regulations introduce more realistic cycles like WLTC https://upload.wikimedia.org/wikipedia/commons/thumb/b/be/WL... and real road tests, where particle emissions will be trapped and compared against the lab test, and only a certain % of deviation will be allowed (last time I looked they didn't decided this % yet).