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.