ing of fossil fuels causes the oxidation of the N gas into NO compounds. Once in the earth's atmosphere, the NO gases oxidize to form HNO , or nitric acid. Nitric acid also then dissolves and ionizes in the water of the atmosphere to lower the pH.
             " Not all sulfates and nitrates in the air or in precipitation contribute to the acidity of the air or precipitation. Acidity in solution is a function of the concentration of hydrogen ions. Some sulfate and nitrates in the air and in precipitation may be associated with cations other than hydrogen, such as ions of calcium and ammonium. Thus, the acidity of deposition is the result of influences of the variety of cations and anions that may be present and in general cannot be identified with one or two an
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