Acid rain is a type of meteorological precipitation, which is a mixture of moisture and the smallest particles of nitrogen oxide and sulfur dioxide in concentrations exceeding the normal natural background. Sources of acid rain are natural processes, such as volcanic activity or decay of plant residues, as well as human activities, expressed in emissions of sulfur dioxide and nitrogen oxides into the atmosphere from the combustion of fossil and motor fuels. Acid rain is formed when emissions of gases react with water, oxygen, and other chemical elements in the atmosphere to form various acidic compounds.
In the second half of the 20th century, it became obvious to scientists that acid rains cause great damage to the environment, reduce soil fertility, leading to the seepage of toxic metals into aquifers, destroy buildings and cultural monuments, pipelines, and render vehicles unusable. The economic losses are also great. For example, on the East Coast of the United States, one study estimates that acid rain damages $13 million annually.
Modern scientists are trying to find a way to combat the formation of acid rain. For example, one of the methods is aimed at improving the technology for removing sulfur compounds from air emissions from industrial plants and power plants, for which a device called a scrubber is usually used. Some governments are enacting laws to limit the amount of pollutants in vehicle exhaust.
The term "acid rain" was coined in the mid-19th century, when British scientists noticed that air pollution in industrialized central England was causing rain that was more acidic than usual. So, in 1872, Robert Smith in his book “Air and Rain: The Beginning of Chemical Climatology” first described the formation of smog in the English city of Manchester, which later led to the study of the formation of acid rain.