ACID RAIN

  Acid rain describes any form of precipitation that contains high levels of nitric and sulfuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth. Normal rain is slightly acidic, with a pH of 5.6, while acid rain   generally has a pH between 4.2 and 4.4 . Causes of acid rain Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but most acid rain is a product of human activities. The biggest sources are  coal-burning power plants , factories, and automobiles. When humans burn  fossil fuels , sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ) are released into the atmosphere. Those  air pollutants  react with water, oxygen, and other substances to form airborne sulfuric and nitric acid. Winds may spread these acidic compounds through the atmosphere and  over hundreds of miles . When acid rain reaches Earth, it flows across the surface in runoff water, enters water ...