It's not that hard to find the source on any CA freeway.
"Smoker" cars are all over the place. It's amazing to me that these things are allowed anywhere near the road, but there they are, polluting about 10,000 times more than any modern or any older maintained vehicle.
The Legislature allows the CHP to go easy on these folks, however, for reasons you may guess.
In Virginia you have to have a vehicle emissions test when you renew your registration.