How to control air pollution by icreasing Height of Stack or Changing the fuel for boiler?

One thing the previous poster forgot to mention: increasing the height of a smokestack does little if anything to control air pollution. In the U.S., many industries tried to increase the height of their smokestacks in the early 70s to take advantage of a loophole in the Clean Air Act, but an amendment was ped in 1977 that removed this loophole.