All Combustibles present environmental problems, especially in some geographic conditions that allow air-borne matter to collect and fall into our lungs, water sources, crops, etc. . Visit Boise, Idaho in winter and be prepared to observe the disgusting brown-gray haze as far as eye can see created from all the wood fireplace burns (and garbage included), really depressing in a normally beautiful area. On a more upbeat note, large diesels used for back-up power supplies have cleaned up their exhaust emissions to a pretty decent level, and I have seen some reports that show the exhaust product is cleaner than the incoming air from certain zones in China and India, who would have known that we can now use them to "purify" the air in these "look the other way" areas. Oh, the irony.......... It is hard to really understand the connection amongst the VW-Audi-Porsche engineers, and it appears that the Audi guys had more influence on the VW diesels, but it really does not speak well for the entire group.