What is acid rain?

• Pollutant acid gases dissolving in water in the atmoshere and falling as snow, fog or rain.

• The acidity of acid rain can be measured using the Ph scale.

• "Natural" rain water is already slightly acidic, with a pH of 5.6. This is because CO₂ (carbon dioxide) dissolves into the rain water and produces carbonic acid. Any precipitation that has a pH less than 5, is considered "acid rain".

• A small change in Ph can be a large change in acidity, as a drop from Water with a Ph of 5 is ten times more acidity than a water with a Ph of 6.

• The two principal acids in acid rain are H₂SO₄ (sulfuric acid) and HNO₃ (nitric acid). Their sources are SO₂ (sulfur dioxide) and NO_x (nitrogen oxide).