Toxic exhaust from power plants accounts for much of the nation's air
pollution. Congress's 1990 Clean Air Act required that all electric generating
plants in the U.S. reduce their emissions by 2010. In response, many plants
have already added scrubbers to their chimneys. These industrial pollution
control devices can remove toxic substances from exhaust streams, or neutralize
them so that they are harmless or even recyclable. Ironically, the more robust
the plume of smoke rising from a smokestack, the more likely it is "scrubbed"
exhaust. So-called "wet" scrubbers can increase the proportion of water in
waste gases, plumping up smoke plumes.