Plural: acid rains

Rain containing acids that form in the atmosphere when industrial gas emissions combine with water; SYN. acid precipitation.
Acidic precipitation thought to be caused principally by the release into the atmosphere of sulfur dioxide (SO2) and oxides of nitrogen. Sulfur dioxide is formed by the burning of fossil fuels, such as coal, that contain high quantities of sulfur; nitrogen oxides are contributed from various industrial activities and from automobile exhaust fumes.
Acid deposition occurs not only as wet precipitation (mist, snow, or rain), but also comes out of the atmosphere as dry particles or is absorbed directly by lakes, plants, and masonry as gases. Acidic gases can travel over 500 km a day so acid rain can be considered an example of transboundary pollution.
Acid rain is linked with damage to and the death of forests and lake organisms in Scandinavia, Europe, and eastern North America. It also results in damage to buildings and statues. US and European power stations that burn fossil fuels release some 8 g/0.3 oz of sulfur dioxide and 3 g/0.1 oz of nitrogen oxides per kilowatt-hour. According to the UK Department of the Environment figures, emissions of sulfur dioxide from power stations would have to be decreased by 81% in order to arrest damage.
The main effect of acid rain is to damage the chemical balance of soil, causing leaching of important minerals including magnesium and aluminum. Plants living in such soils, particularly conifers, suffer from mineral loss and become more prone to infection. The minerals from the soil pass into lakes and rivers, disturbing aquatic life, for instance, by damaging the gills of young fish. Lakes and rivers suffer more direct damage as well because they become acidified by rainfall draining directly from their catchment.