In the next few weeks, thousands of tons of largely invisible smokestack pollutants rising from the Tennessee Valley Authority coal-fired power plant nearest the Great Smoky Mountains will be replaced by a billowing plume of steamy water vapor.

TVA officials said Thursday the $277 million smokestack "scrubber" system is nearly complete at the plant near Oak Ridge and should go into operation in early December, after three years of construction.

The scrubber is expected to remove more than 90 percent of sulfur dioxide emissions. These cause manmade haze and acid rain that plague the Smokies national park.

TVA plans to add scrubbers to its two other coal plants in eastern Tennessee by 2013.