Coal is deemed a “dirty” fuel because it contains many natural chemical substances. When coal is burned, it emits: sulfur dioxide, fluoride compounds, mercury, uranium, and other radioactive metals, all highly toxic substances. Coal plants continue to be the largest emitters of mercury into the atmosphere within North America. Soot is also a result of burning coal. Soot is proven to be a severe respiratory agitator, causing and irritating asthma attacks, decreased lung function, and overall respiratory complications.
It is thought that coal can be burned “cleanly” in large-scale factories, meaning it would not emit as many harmful pollutants. However, it is expensive to install the necessary machinery to “clean” coal burning. Coal is still the most widely used source for electricity in industrialized and non-industrialized nations. In the United States, the amount of carbon dioxide emissions (a greenhouse gas) outweighs the amount of carbon dioxide emissions from burning fossil fuels.
Coal burning is the largest source of atmospheric sulfur dioxide. Cleaning coal involves the costly process of removing sulfur from the coal before it is burned. Another means of reducing sulfur dioxide emission levels is to substitute coal with oil, natural gas, or low-sulfur coal, though these are much more expensive.
With all this in mind, is it even possible to have “clean coal?” Even if sulfur is removed and measures are taken to reduce pollutants, there are still emissions of dangerous greenhouse gases into the atmosphere. The idea of “clean coal” is especially intriguing at the moment because newly elected President Obama claims that he will work toward using safer, “clean” coal; however, it seems apparent that even “clean” coal is dangerous. So is calling it “clean” coal an attempt to lessen the scrutiny of electricity production or is it a fact that coal can be burned with a significant reduction in toxic and polluting emissions?
Baird, Colin. "4.24 Coal is called a "dirty" fuel." Chemistry in Your Life. 2nd ed. New York: W. H. Freeman & Company, 2006. 159-161.