Since then, research has shown that atmospheric pollutants, including sulfuric and nitric acids, can be transported long distances by wind currents. Eventually, these acids, when mixed with rain, produced acid precipitation and have far-reaching ecological effects. Naturally occurring atmospheric acids originate form volcanoes, forest fires, and bacterial decay and contribute to the natural acidification of precipitation. Combustion of coal and oil release massive amounts of sulfur oxides and nitric oxides into the atmosphere. These oxides, when mixed with water vapor, form sulfuric acid and nitric acid which then fall back to the ground as acid precipitation.
Rain only becomes acidified when acids in the atmosphere cause the pH to drop below normal.
In industrial areas of the world, human-made acids in the air significantly decrease the pH of precipitation. Acidified precipitation has many adverse effects on the environment. Throughout the world, lakes and rivers and their fish are dying at an alarming rate. Acid precipitation also causes damage to forests and crops. In Czechoslovakia, researchers have estimated that 300,000 acres of forest has been destroyed by acid precipitation.