What is Acid Rain and What Causes It?
“Acid rain” is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry. Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved, and the types of fish, trees, and other living things that rely on the water. Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms.
Scientists discovered and have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acidic conditions in the atmosphere. In the United States, about 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal (EPA Acid Rain website). Acidic conditions develop when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid. The acidic compounds then fall to or are deposited on the earth’s surface. “Acid rain” is a broad term used to describe several ways that acids fall out of the atmosphere. Acid rain is usually used in reference to rain, snow, sleet, and hail. A more precise term is acid deposition, which includes all forms of precipitation but also includes deposition of dry particles and gases as well as occult or cloud, fog
