Ok, guys, cut the personal attacks, and stay on topic.
As a note, the smoke from the Big Boy isn't as bad as you may think... Most, if not all, of the visible/black stuff in the exhaust is ash or unburnt coal. This falls back to the ground, and isn't too bad (a lot of people actually use loco ash as fertilizer to some degree...). It's the invisible stuff that is an issue, and both steam and diesel put them out. The fact that it's coming out isn't always good, but it also depends on the coal being burnt at the time, and it's ash content. Lower grades of coal generally burn best with black smoke; higher grades of coal can be burnt with clear smoke. Welsh steaming coal is among the good coals. The Romney, Hyth & Dymchurch railway in the UK is seeing this at the moment, as they don't have access to higher grade coals.
Regards
