How Acidic Is Your Rain?
ES1807  Sulfate Ions and Acid Rain

Acid in rainfall has a variety of natural sources. Carbon dioxide in the air combines with water to form carbonic acid. Volcanoes and forest fires add sulfur compounds to the atmosphere that form sulfuric acid. Although acid rain has many natural causes, their combined effect is relatively small.

The strong levels of acid rain observed in modern times are primarily the result of human activities. Over 90% of the sulfur dioxide released into the atmosphere today comes from the combustion of fossil fuels. Coal-burning power plants represent the largest source of sulfur dioxide entering the atmosphere. The sulfur dioxide combines with water to produce the sulfate ions that are present in acid rain.

  !   Move your cursor over the map to reveal the locations of fossil fuel-burning electric generation plants in the US.

Winds generally blow from west to east over the United States, and they are capable of carrying atmospheric pollution far from its original source.

5. Which areas have the highest concentrations of sulfate ions (SO42-) in rainwater?

6. How do the locations of fossil fuel-burning power plants compare to the location of areas with high concentrations of sulfate ions?

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