The amount of sulfuric acid released by an individual power plant depends on the sulfur content of the fuel it burns, as well as operating and air pollution control practices at the plant. Most sulfuric acid released into the air by natural sources comes from volcanoes. Sulfuric acid released into the environment by human activities outside the utility industry comes mainly from plants that manufacture it, pulp and paper mills, phosphate fertilizer factories, copper smelters, and steel fabrication facilities. Industries reporting to EPA released 9,880 tons of sulfuric acid into the environment in 1996. Nearly all was released into the air.
Power plants release both sulfuric acid and sulfur dioxide into the air from their stacks.
In the air, sulfur dioxide can change chemically to form dilute sulfuric acid. Some of the sulfuric acid formed in the air quickly loses its acidity by combining with ammonia that is naturally present there. Some forms tiny liquid droplets or thin films on tiny dust particles. As droplets and particles formed in the air or released from power plant stacks-incorporate more water, the sulfuric acid they contain becomes more dilute. By the time these droplets and particles reach surface soil and water by settling to the ground or washing out of the air in rain and snow, the sulfuric acid they contain is very dilute.