Coal is dirty in many ways, from staining the hands of miners to contributions to climate change, but this striking new paper shows that by creating air pollution (presumably primarily particulate matter) coal kills: thousands a year. Here is a one-tweet summary:
For the full paper, see the link.
Update 1/27: Prof. Auffhammer adds some personal recollections.
Update 3/21: NY Times article on the effects of a coal plant closing. It's a sympathetic view of how the closure will affect the lives of locals.