To generate the electricity we use every day, coal-fired power plants burn coal to produce energy. Small amounts of mercury exist naturally in coal. When coal is burned for power generation, mercury vapor is released. If unchecked, this vapor escapes into the atmosphere where it is carried on air currents. However, on average, mercury content in U.S. coal is relatively low and mercury air emissions from U.S. power plants are estimated to be less than 50 tons per year, which accounts for about one percent of the total global mercury output. And power plants are not the sole source for the release of mercury into the environment.

• The design of the treatment system,
• The condition of the power plant equipment and type of boiler,
• How the coal is filtered and the particles collected,
• The treatment of coal prior to combustion,
• Mercury content of the coal