i just found this after exploring another AEP plant in Ohio.. they installed SCR's (scrubber technology) to reduce CO2 and mercury output. they had a similar 'blue haze' problem.. this is what the AEP website says..
Conversion to low-sulfur coal at one unit of our Tanners Creek Plant in Indiana was completed last year. More than 45 percent of our coal-fired power plant capacity will be equipped with SCRs and more than 48 percent will have FGDs. These actions are projected to reduce NOx emissions by 79 percent and SO2 emissions by 65 percent from 1994 levels by 2010, while generating 17 percent more electricity annually. Mercury emissions will decline an additional 55 percent from current levels by 2010.
The improvement in SO2 and NOx environmental performance at our coal plants was a trade-off. Pollution control systems consume additional energy and reduce plant efficiency per unit of electrical output. In addition, SO2 scrubbers will increase CO2 emissions as the limestone chemistry captures SO2 but releases CO2.
Installing leading-edge technology can sometimes create unexpected consequences. This occurred at AEP�s Gavin Plant, near Cheshire, Ohio, after SCR equipment was installed to reduce NOx emissions in 2002. The SCR equipment reduced the NOx emissions but also created bluish plumes (sulfur trioxide) that touched down in Cheshire and caused considerable community upset.
We took immediate steps to mitigate the blue plume and fixed the problem within months. We developed a process that we intend to use to control emissions at other power plants equipped with both FGDs and SCRs. The Gavin Plant experience was a painful and costly lesson, but resulted in a solution to prevent the same consequences at other plants.
http://www.aep.com/citizenship/crreport/environmentalperformance/committedtocleanair.asp