Acid rain is rain or any other form of precipitation that is unusually acidic, meaning it has elevated levels of hydrogen ions (H+). It can have harmful effects on plants, animals, and aquatic ecosystems. The main causes of acid rain are emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from power plants, factories, and vehicles. These emissions can be transported long distances by winds and then react with water vapor in the atmosphere to form acids, such as sulfuric acid and nitric acid. The presence of these acids in rain can lead to acidification of lakes, streams, and soils, causing damage to aquatic life and vegetation. Acid rain can also contribute to the deterioration of buildings and other structures, as well as damage to forests and crops.