Scientific American: On a visit to China a few years back, I asked a local official about pollution controls after enjoying my first sour, gritty taste of the country`s air. Chinas new coal-fired power plants and other industrial boilers often came equipped with expensive scrubbers to clean acid rain and smog-forming sulfur dioxide out of the hot mix of gases that went up and out the smokestack. But the scrubbers required energy to run, this official noted, and therefore were shut off except on days when dignitaries...