Factories release sulfur dioxide and nitrogen oxides into the atmosphere through the burning of fossil fuels. These gases either mix with rain or fall to the surface as particulate matter and create harmful acidic conditions in natural areas. While pollution remediation efforts have reduced the emissions of sulfur dioxide, nitrogen oxides remain a problem that will continue as long as fossil fuels are widely used.
Acid rain results from both wet and dry material that interacts with precipitation and then eventually enters soil and streams. In particular, it comes from sulfur dioxide and nitrogen oxides released by the burning of fossil fuels, like petroleum and coal, and natural sources such as from volcanic eruptions. When these gases mix with precipitation, they form acid rain, in essence sulfuric and nitric acid solutions. Prevailing winds can carry acidic precipitation far from factories and power plants, resulting in extensive damage to forests, streams and wildlife.
Sulfur and Nitrogen
Power plants that generate electricity produce 67 percent of the sulfur dioxide and 25 percent of the nitrogen oxides in the atmosphere within the United States. Acid rain does not come solely in the form of acidic precipitation; sulfur and nitrogen compounds can also fall as dry material or particulates from factory emissions. These materials interact with streams and soil to produce acidic bodies of water and soil conditions. Natural rainwater has a pH of 5.6, which is slightly acidic due to presence of carbon dioxide. In some areas of the United States, such as the East and West coasts, sulfur dioxide and nitrogen oxide emissions have lowered the pH of precipitation to below 3 -- a pH level that can cause the decline of forests and aquatic populations.
Fossil Fuel Pollution
Roughly 85 percent of energy produced in the United States comes from the burning of fossil fuels. Prior to industrialization, it is estimated that naturally occurring sulfur dioxide and nitrogen oxides created a soil pH of roughly 5 in forested areas of the eastern United States. In contemporary times, the pH there has fallen on average to 3.7, which is two to three times more acidic. Sulfur dioxide emissions from factories are primarily due to the burning of coal, and the burning of all fossil fuels causes nitrogen oxide pollution.
The most effective way to combat acid rain is to curb sulfur dioxide and nitrogen oxide emissions from factories and power plants. Some progress toward this goal has been made. For example, sulfur dioxide emissions were cut 33 percent between 1983 and 2002. Power plants and factories have reduced sulfur dioxide emissions by cleaning the coal prior to burning and using scrubbers in the smokestacks to remove the sulfur dioxide before it is emitted into the atmosphere. Nitrogen oxides have likewise been reduced through the use of smokestack scrubbers as well as from catalytic converters on vehicles. Nitrogen oxides, however, remain a significant problem due to the ever-increasing use of petroleum for energy. The Environmental Protection Agency expects that increased use of alternative energy sources in the future will reduce harmful emissions.
- U.S. Environmental Protection Agency: What Is Acid Rain?
- The Encyclopedia of Earth: Acid Rain
- Department of Chemistry Washington University: Acid Rain Inorganic Reactions Experiment
- Union of Concerned Scientists: The Hidden Cost of Fossil Fuels
- U.S. Environmental Protection Agency: Reducing Acid Rain
- Scientific American: Sour Showers: Acid Rain Returns -- This Time It Is Caused by Nitrogen Emissions
- Photo Credit Kim Steele/Photodisc/Getty Images