Burning trash is a lot worse than coal. Trash contains all kinds of trace compounds from the manufacturing process that get into the air during burning. Some noxious compounds are creating during the burning process as well. While you can try to filter out the bad stuff, the record of trash-burning plants is very bad, and several have been closed.
Even burning wood is worse than coal. A recent article by the Wall Street Journal found that here in the US, 85 out of 107 wood burning plants have been cited with at least minor violations of environmental laws in the past five years (
http://online.wsj.com/article/SB10001424052702303740704577524822063133842.html ).
