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What causes acid rain?

Acid deposition is a general term that includes more than simply acid rain. Acid deposition primarily results from the transformation of sulphur dioxide (SO₂) and nitrogen oxides into dry or moist secondary pollutants such as sulphuric acid (H₂SO₄), ammonium nitrate (NH₄NO₃) and nitric acid (HNO₃). The transformation of SO₂ and NOx to acidic particles and vapours occurs as these pollutants are transported in the atmosphere over distances of hundreds to thousands of kilometers. Acidic particles and vapours are deposited via two processes - wet and dry deposition. Wet deposition is acid rain, the process by which acids with a pH normally below 5.6 are removed from the atmosphere in rain, snow, sleet or hail. Dry deposition takes place when particles such as fly ash, sulphates, nitrates, and gases (such as SO₂ and NOx), are deposited on, or absorbed onto, surfaces. The gases can then be converted into acids when they contact water.

http://www.ec.gc.ca/acidrain/acidfact.html

Labels: air, ocean, water