Natural sources of sulfuric acid include volcanoes, forest fires and the decomposition of biological matter, but human beings produce more than 100 million tons of sulfuric acid every year. More sulfuric acid is produced industrially than any chemical compound besides water.
Sulfuric acid is manufactured for use in fertilizers, for processing ores and wastewater, for refining oil, and for making batteries, dyes and drain cleaners. The production of sulfuric acid involves burning sulfur to produce sulfur dioxide, which is then oxidized to produce sulfur trioxide. When diluted with water, sulfur trioxide forms sulfuric acid. About 75 percent of the sulfur dioxide humans produce is the result of burning fossil fuels. Sulfur dioxide combines with water molecules in the atmosphere to form sulfuric acid, which is one of the components of acid rain.