Acid rain

Precipitation with an abnormally high level of acidity (pH less than 5). It is caused by emissions of nitrogen and sulfur oxides from factories, power plants, and vehicles, which mix with water vapor in the air, transform into acidic solutions, and fall to the Earth's surface with rainwater. It causes serious damage to agriculture, crops, soils, aquatic ecosystems, and even buildings and infrastructure; it also causes significant respiratory problems.