Piece of advice to Greenpeace: US-based coal-fired plants is NOT part of the problem.
Thanks to very strict EPA regulations, coal-fired powerplants must have extensive emission controls to drastically reduce the smoke and particulate output and also filter out the sulfur that becomes poisonous and highly acidic sulfur dioxide gas. They're certainly WAY cleaner than any coal-fired power plant in China, that's to be sure.
What about mercury?