Sulfur Dioxide A Major Primary Pollutant

Sulfur dioxide is produced when sulfur or sulfur-containing compounds are burned in air. 

Most of the coal burned in the United States contains sulfur in the form of the mineral pyrite (FeSg). The percentage (by weight) of sulfur in this coal ranges from 1 to 4%. The pyrite is oxidized as the coal bums, forming SOg. 

Large amounts of coal are burned in this country to generate electricity. A 1000-megawatt (MW) coal-fired generating plant can burn about 700 tons of coal an hour. If the coal contains 4% sulfur, that equals 56 tons of SOg an hour, or 490,560 tons of SOg every year. About 800 million tons of coal are burned each year to produce electricity. 

Oil-burning electric generating plants can also produce comparable amounts of SOg because some fuel oils can contain up to 4% sulfur. The sulfur in the oil is in the form of compounds in which sulfur atoms are bound to carbon and hydrogen atoms. Gasoline contains relatively low concentrations of sulfur-containing compounds. Even so, the EPA has mandated that the maximum concentration of sulfur-containing compounds be reduced from 120 ppm in 2004 to 90 ppm in 2005 and to 30 ppm by 2006. Further mandated reductions may be expected. 

States that rely mainly on coal for their electricity production and industrial furnaces have the highest SOg emissions in the United States. Operators of all coal-fired burners are under EPA orders to eliminate most of the SO before it reaches the exhaust stack. 

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