What is acid rain? Acid rain is the term for pollution caused
when sulfur and nitrogen dioxides combine with atmospheric
moisture. The term 'acid rain' is slightly misleading, and would
be more accurate if deemed 'enhanced acid rain', as rain occurs
acidic naturally. Acidity is measured on what is know as the pH
scale. Fourteen is the most basic, seven is the most neutral, and
zero is the most acidic. Pure rain has a pH level of 7, which is
exactly neutral. The acidity of rain is determined by the pH of
pure water in reaction with atmospheric concentrations of
carbon dioxide, resulting in carbonic acid. These particles
partly dissociate to produce hydrogen ions and bicarbonate
ions. A bicarbonate atom is an ion formed by one hydrogen
atom, one carbon at atom, and three oxygen atoms, and is very
effective in natural waters at neutralizing hydrogen ions and
reducing acidity. The dissociation results in the natural acidity
of pure rain, which is moderately acidic at a pH of 5.7. Rain
less than 5.7 is considered 'acid rain', meaning it has reacted
with acidic atmospheric gases other than carbon dioxide, such
as sulfur dioxide and nitrogen dioxide. Sulfur dioxide is
produced by electric utilities, industrial, commercial and
residential heating, smelters, diesel engines and marine and rail
transport, which creates sulfuric acid in rain. Nitrogen dioxide
will also react with the rain, caused largely by transportation
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