Coal produces nearly half the electricity in the U.S., but the mercury, sulfur dioxide and carbon dioxide it emits also make it one of the most controversial energy sources. New EPA regulations and a national Sierra Club campaign to try to shutter the industry have added to rising anti-coal sentiment. For many environmental activists, coal represents an old, dirty source of power, but for coal-mining communities around the country, the story is different.This is part three of Coal at the Crossroads. The full audio and a slideshow are below.