Acid rain occurs when sulfur dioxide and nitrogen oxides are released into the air where they rise and mix with water, oxygen and other chemicals. Sulfur dioxide and nitrogen oxides dissolve very easily in water and can travel great distances to combine with the moisture in the air.
Humans are the main cause of acid rain, according to the EPA, because many different chemicals get released into the air as a result of burning fossil fuels, exhaust from cars and the use of aerosol cans. Natural rain is slightly acidic, but human activities make it worse. Acid rain can cause damage to crops, trees, rivers, animals and lakes.