Acid in rainfall has a variety of natural sources.
Carbon dioxide in the air combines with water to form
carbonic acid. Volcanoes and forest fires add sulfur
compounds to the atmosphere that form sulfuric acid.
Although acid rain has many natural causes, their combined
effect is relatively small.
The strong levels of acid rain observed in modern times
are primarily the result of human activities. Over 90%
of the sulfur dioxide released into the atmosphere today
comes from the combustion of fossil fuels. Coal-burning
power plants represent the largest source of sulfur
dioxide entering the atmosphere. The sulfur dioxide
combines with water to produce the sulfate ions that
are present in acid rain.
! Move your cursor over the map to reveal the locations
of fossil fuel-burning electric generation plants in