At substantial risk of sounding like a left-coast snob, the draconian emission laws in California make this a delightfully rare occurrence. Public transit buses are CNG or electric. Bi-annual smog checks will down your car until it passes too. And for the wise-guys who cheat the system, there are random laser traps at freeway on-ramps to sample your exhaust under heavy engine load and take a picture if you are too dirty. You then get a notice to bring your car to a state inspection center within 30 days.

I travel an awful lot for work and going from state-to-state I really notice a difference. Even at gas stations... one could almost forget how badly gasoline stinks with the 10 pounds of vapor recovery, vacuum crap on the pump nozzles in CA, until you go to anywhere else. It hits me like a ton of bricks, it's nauseating.

With new Federal standards to scrub diesel particulate emissions rolling out with the new ULSD fuels, things will get even better.

It is easy to dismiss all of this as a bunch of misguided Utopian crack-pot California nuttiness, except for the fact that it works! The thick brown layer over the region is about 70% less now than it was when I moved here in 1986.