Effects of acid rain on a forest, in the Czech Republic

Acid rain is rain that is unusually acidic and highly corrosive in nature. It is rain with high levels of hydrogen ions (low pH). It may be defined as "rain water having pH less than 5.6".

Acid rain can have harmful effects on plants, animals and humans. It is caused when gaseous compounds of ammonium, carbon, nitrogen, and sulphur are released into the atmosphere. The wind carries the gases high into the sky. There the compounds react with the water in the atmosphere and acids are made. In 1852, Robert Angus Smith showed the relationship between acid rain and atmospheric pollution in Manchester. He coined the term "acid rain" in 1872.