(cars, trucks, planes, etc.) and electric utilities, producing
             nitric acid. There is a certain degree of naturally occurring
             acidity in rain water. This acid is from reaction with alkaline
             chemicals, found in soils, lakes and stream, and can occasionally
             occur when a volcano erupts as well. Bacterial action in soils
             and degasing from oceanic plankton also contribute to the
             acidity found in rain. More than 90% of the sulfur and 95% of
             the nitrogen emissions which occur in North America are due to
             the pollution created by humans.1 How Is Acid Rain Formed?
             Acid rain consists mainly of acids formed in the atmosphere. It
             consists of the oxides of sulfur, SO2 and SO3, and of nitrogen
             NO and NO2. Let us examine the major contributor to acid
             rain, sulfur oxides. Natural sources which emit sulfur dioxide
             include volcanoes, sea spray, plankton and rotting vegetation.
             Despite these natural occurrences, the burning of fossil fuels
             (such as coal and oil) can be largely blamed for the emissions.
             The chemical reactions begin as energy from sunlight, in the
             form of photons, hit ozone molecules (O3) to form free oxygen
             (O2), as well as single reactive oxygen atoms (O). The oxygen
             atoms react with water molecules (H2O), producing electrically
             charged, negative hydroxyl radicals (HO). These hydroxyl
             radicals are responsible for oxidizing sulfur dioxide and
             nitrogen dioxide, which produces sulfuric acid and nitric acid.
             ...