I'm not real interested in joining a debate, but there are few facts that have been left out of the discussion:

The laws of physics have not been altered to suit the government, even the CALIFORNIA government. Physics says that for every pound of material burnt a pound of material remains. The simplest way to understand it is that in the case of our trucks a pound of diesel fuel is converted to a variety of gases and particulate (soot, nitrous oxide, etc).

The idea of the emissions components began in the 1970's with good intentions of altering specific components released into the atmosphere and rendering them into a less harmful form. Specifically for gasoline engines, the prefered fuel for American consumers. Gasoline as a fuel contains far less energy per unit than diesel fuel does, and gasoline engines convert this fuel to work far less efficiently than a diesel engine does, and at the time gasoline contained heavy metals as additives so the idea of converting these polutants to something less harmful was a rather altruistic idea.

It has since gotten off the track. The diesel trucks that we drive today have far superior engines and engine management systems than the gas trucks of the 1970's yet stock we get about the same fuel mileage of a 1979 Ford Camper Special with a 390 cubic engine. Why? because of all of the garbage installed in the name of clean air. Yes these trucks measure very clean for the specific pollutants examined during a smog test, but the laws of nature have yet to be adjusted due to federal or state mandate. A pound of fuel still equals a pound of exhaust.

If removing ill advised equipment cuts the fuel consumption per mile delivered in half, then so to has the polution created per mile delivered. This of course says nothing of the positive economic impact to our wallets.