Conservative Acoustic Foam
I think they already do have scrubbers that do what they can. But at the sheer volume that coal is burned in order to create the heat to ultimately convert to electricity, there's only so much that can be done. The greenest solution is finding alternatives that create less by-product from being burned (natural gas being the most popular right now), or of course making solar/wind/etc more efficient. The problem there is of course politics of lobbying from the coal industry being very entrenched, so change is unpopular.