Although you are right in the fact that they need to clean it up and I'll be the first to admit that I have always worked hard so that my truck didn't smoke even though we have no testing, they really do need to do they're homework on who is polluting the air.

Our trucks contribute very little to the air pollution even when they do smoke. The smoke is almost completely solid materials that float back down to the ground. It's essentially ash.

In the big rig world of pollution and law enforcement it is the excepted rule that all smoke must clear in the air within 3 seconds to be exceptable. I would have to assume that the same standards are being used.

A modified Diesel engine emits more than what you can see; there's a lot of ultra-fine particles that carry through the atmosphere, are known carcinogens and like to get embedded in lungs. Gasoline engines can also emit fine particulate matter. Hot-rodded Diesels also emit NOx like crazy, just like modified gasoline engines. The only thing that Diesels emit substantially less than gasoline engines is CO.

I would have to be convinced that much of this particulate actually makes it into the upper atmosphere adding to the greenhouse gasses. Between heat, humidity and rain it seems to me that it would be flushed out of the air in pretty quick order. But I'm also no scientist either.

Particulate matter is horrible on the lungs; asthma, lung cancer, atherosclerosis, bronchitis, et cetera. Particulate matter from Diesels is just as bad as from gasoline engines, much higher in volume and quite possibly worse. Global warming from PM emissions is a twentieth or thirtieth concern at best.