[goodpoint]

> automotive is not ... part of a conspiracy

A group of people secretly breaking the law is exactly a conspiracy, by definition: https://www.merriam-webster.com/dictionary/conspire

> A lot of regulated industries self-regulate

Not so easy. Traffic engineers, meteorologists, environmental agencies and other [EU-funded] organizations monitor the air quality constantly and have detailed statistics on how many cars of each model are on the road.

You can easily do the math and see that the numbers do not match expectations.

You cannot tell which brand is cheating but you can tell that the pollution is much, much higher than expected.