As a consequence, the total amount of these substances emitted to the air has declined substantially in the last two decades even as the amount of electric generation has increased substantially. Emissions of carbon dioxide are not subject to regulation under the environmental laws of the United States or Arizona. Coal-fired electric generation also emits trace quantities of hazardous air pollutants, or HAPs. EPA is currently conducting a further study of the impacts on the environment of mercury emissions. The amount of sulfur dioxide, carbon monoxide, carbon dioxide and other substances emitted from coal-burning powerplants is more than offset by reductions in emission of these substances when electricity is used as an energy source.
Electricity is the cleanest, most efficient source of energy in commercial use.
Over the last century, electricity has replaced fossil fuels, including coal, as the source of energy for a wide variety of residential, commercial and industrial processes. Whenever electricity is used instead of fossil fuels in these processes, the result is a net reduction in emissions, because the emissions avoided when electricity is used as a substitute for fossil fuels is greater than the emissions produced when coal is used to generate electricity. Electricity is used as a substitute for fossil fuels when the price of electricity is competitive with the price of the fossil fuels. If the price of electricity increases unduly, fossil fuels will be used as a source of energy rather than electricity, with the result that emissions will increase. Coal-fired electric generation is a low cost source of electricity.