Acid rain is an ugly problem that has been becoming more and more prevalent with increases in the number of vehicles and power stations, as well as other types of fossil fuel burning machines. This is not just a problem in the United States, but all over the world. Since acid rain travels in clouds, these clouds can be blown pretty much anywhere, and can cause trouble wherever they go. Acid rain is not only harmful to people, but also to lakes and rivers, trees, and even buildings.
Two gases that can be acid-forming are carbon dioxide, which forms carbonic acid; and chlorine, which forms hydrochloric acid. The following are the equations for these reactions, respectively:
2Cl2 (g) + 2H2O (l) --> 4HCl (aq) + O2 (g)
These two reactions, however, are not the most common causes of acid rain. Carbonic acid is weak and chlorine gas is rare. The more common cause of highly acidic rain is sulfur dioxide and various oxides of nitrogen. Sulfur dioxide (SO2) makes up close to 70% of acidic rain, while the nitrogen oxides (mainly NO2 and NO3, but collectively called NOx) make up the other 30%. The equations for these reactions are as follows, respectively:
2NOx (g) + H2O (l) --> 2HNOx (aq)
There are two ways in which these types of acid rain may fall to earth: wet deposition and dry deposition. Wet deposition includes acidic rain, fog, and snow. Dry deposition are acidic gases and particles. About one half of the acidity in the atmosphere falls back to earth by dry deposition. Regardless of how acid rain returns to earth, it still is very harmful to people, as well as other animals and the environment.
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