Acid Rain is a term used to describe different ways in which acid falls from our atmosphere. A better term would be Acid Deposition, which is made up of two parts, wet and dry deposition. Wet deposition is composed of acidic rain, fog, or snow, where as dry deposition refers to acidic gases and particles. This deposition contains higher than normal amounts of nitric and sulfuric acids.
The leading cause of acid deposition is the release of sulfur dioxide and nitrogen oxide during fossil fuel combustion. These gases, which are responsible for acid deposition, are normally the result of electric power generation and the burning of fossil fuels such as coal. Sulfur dioxide is the byproduct of power-production companies and industries that burn fossil fuels like coal and oil as a source of energy. However, it can also be caused by natural sources, such as rotting vegetation, plankton, sea spray, and volcanoes. Nitrogen oxide is produced in firing processes which involve extremely high temperatures; for example utility plants, automobiles, and chemical industries. Nitrogen oxide can also be formed by natural processes like lightning, volcanic eruptions, forest fires, and action of bacteria in the soil.
