primarily at reducing emissions that cause acid deposition (i.e., acid rain). However, SO2 reductions also should improve visibility in Class I areas in the United States, particularly in the East.

Table D-1 shows the results of an analysis funded by the U.S. Department of Energy (DOE) of power plants in relation to Class I ''prevention of significant deterioration'' (PSD) areas. The percentage of total coal-fired power-plant capacity affected by an SO2 reduction requirement would be 31% within a 100-mile radius of a Class I area, increasing to 61% within 150 miles and 75% within 200 miles; 85% of total SO 2 emissions arise from boilers within 200 miles of Class I areas (Trexler, 1990).

TABLE D-1 Power Plants and Class I Areas

Power Plant

Boilers, No.

Capacity, 103 MW

SO2 Emissions, 106 tons

Total coal-fired boilers




Within 100 miles of Class. I area




Within 150 miles of Class I area




Within 200 miles of Class I area





Source: Trexler, 1990.

Sulfur Dioxide Control Technologies

Over 150 flue gas desulfurization (FGD) systems in power plants with approximately 72,000 MW of capacity are now operating in the United States to control SO2 emissions (Dalton, 1990). About one-fifth of the total coal-fired capacity is covered by the FGD systems, of which about

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