The diesels in question are overwhelmingly large low compression direct injection diesels, which are without a doubt more polluting than the small high compression VW and MB indirect diesels of the '80-early '90's. Today, both VW and MB produce high compression direct injection diesels that are much much cleaner than those old smoke belching trucks of yesteryear. The introduction of biodiesel blends into the fuel stream can help all diesels to clean up their act. I'm currently working on a system to further reduce NOx emissions in conjunction with the use of biodiesel fuels.