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Air Pollution Creates Acid Rain
Scientists have discovered that air pollution from the burning of fossil fuels is the major cause of acid rain.
The main chemicals in air pollution that create acid rain are sulfur dioxide (SO2) and
nitrogen oxides (NOx). Acid rain usually forms high in the clouds where sulfur dioxide and nitrogen oxides react with water,
oxygen, and oxidants. This mixture forms a mild solution of sulfuric acid and nitric acid. Sunlight increases
the rate of most of these reactions. Rainwater, snow, fog, and other forms of precipitation containing those
mild solutions of sulfuric and nitric acids fall to earth as acid rain.
Acid rain does not account for all of the acidity that falls back to earth from pollutants. About half of the
acidity in the atmoshpere falls back to earth through dry deposition as gases and dry particles.
The wind blows these acidic particles and gases onto buildings, cars, homes, and trees.
In some instances, these gases and particles can eat away the things on which they settle.
Dry deposited gases and particles are sometimes washed from trees and other surfaces by rainstorms.
When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic
than the falling rain alone. The combination of acid rain plus dry deposited acid is called acid deposition.
Sources of SO2 | Sources of NOx
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