Southern AERA Quarterly Activity Bulletin of The South Carolina Department of Natural Resources-Southeast Regional Climate Center
Volume 4, No. 2
What is Acid Rain?
Acid rain is an environmental problem that has been gaining recognition due to the damage it causes. The onset of acid rain began with the industrial revolution. This environmental problem is the result of air pollution from industrial sources as well as emissions from vehicles. Acid rain has been known to cause damage to trees, streams, lakes, animals and even man made structures.
The acidity of a substance is measured on a pH scale. The pH scale ranges from 0 to 14, and on this scale, 7 is considered to be neutral. Anything above 7 is considered to be alkaline, or basic, while anything that has a pH below 7 is considered to be acidic. The figure below shows the pH scale, and the pH of some common substances.
Lemon Unpolluted Distilled Baking Juice Rain Water Soda Ammonia | | | | | | | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acidic Alkaline
Precipitation is considered acidic if the pH falls below 5.6. Although pure or distilled water has a pH of 7, the pH of distilled water is reduced to a slightly acidic value of 5.6 when it is left standing in clean air. This is because of the absorption of carbon dioxide.
The major cause of acid rain is air pollution caused by the burning of fossil fuels. The main chemicals present in air pollution that cause acid rain are sulfur dioxide (SO2) and nitrogen oxides (NOx). These gases have natural sources such as swamps, volcanoes, oceans and lightning, but the amount of gas produced from these sources are of minor significance when compared to the amount of gas that is produced from human activities such as power plants, industrial processes, smelters, and emissions from vehicles. When these gases are emitted into the atmosphere, they react with water, oxygen, and oxidants. This mixture of gases creates mild sulfuric and nitric acids. These acids are brought down to earth with precipitation. About half of the acidity falls back to earth through dry deposition as gases and dry particles. These particles are blown by the wind and eat away at the surfaces they settle on. These dry particles may mix with acidic rain, causing the rain to be even more acidic. This combination of acid rain and dry deposited acid is called acid deposition.
Acid rain has many harmful effects. Acid rain may eventually cause the pH of lakes and streams to decrease, causing harm to aquatic species as well as other species that depend on lake dwelling animals for food. Deformities may occur in fish and amphibians.
Acid rain has a profound effect on trees. The acid rain washes nutrients out of the soil that are needed by the trees. In addition, when dry deposition occurs, the acids have been known to clog the stomata in the leaves of trees, hindering photosynthesis.
Architecture, statues and other man made materials are also negatively effected by acid rain. Monuments, tombstones and other historic artifacts are literally being eaten away by the acidic rain.
Human health is also effected by acid rain and deposition. The most common effects on human health are respiratory problems that include asthma and coughing.
Another negative effect of acid rain and deposition is the haze that it causes. This haze causes limited visibility. This can be dangerous to airplane pilots and upsetting to visitors to national parks who want to enjoy the spectacular views the parks have to offer.
It is important to note that the areas that produce the most sulfates and nitrates are not necessarily the places that are going to have the most acid rain. Pollutants may remain suspended in the atmosphere for a week or longer. In addition, when pollutants are emitted out of tall smoke stacks, the upper level winds will take them in whatever direction they are blowing. It is because of this that circulation patterns and prevailing winds are significant factors in the transfer of acid rain. The source of the acid rain may be as far away as 500 km from the site of the actual rain or deposition. Thus, acid rain is not simply a localized problem, but rather one of a larger, more regional scale.
The Environmental Protection Agency is working to significantly reduce electric utilities' emissions of sulfur dioxide and nitrogen oxides. According to the EPA, there are several ways to reduce the amount of sulfur entering the air. One way is to wash the sulfur out of the coal before it is burned. Another way is to wash the sulfur out of the smoke before it goes up to the smokestack. Vehicles sold in the United States are required to have catalytic converters that reduce the pollution from exhaust fumes. Alternative energy sources are also being explored. These alternative sources of energy include solar power and windmills.
You may not realize it, but everyone can help out when it comes to reducing acid rain. When you turn off lights or appliances that you are not using, you are saving energy. If everyone would save energy, the power company would not have to burn as much fossil fuels to create the energy, therefore reducing the amount of Sulfur Oxides emitted into the atmosphere. Since cars release Nitrous Oxides into the atmosphere, those who walk or car pool are also helping to reduce acid rain.
1. When did acid rain become a problem?
2. What is the pH of unpolluted rain?
3. What would be the pH of the strongest acidic liquid be?
4. Is it likely that the pH of the rain water at your house would you be 7? Why?
5. What is the major cause of acid rain?
6. What are the main chemicals that cause acid rain?
7. Are these gases always from man made sources, or can they be produced naturally? If so, what are some natural sources?
8. What is the combination of acid rain and dry deposited acid called?
9. How would an animal that lives near an acidic lake, but not in it, be effected by the acidity?
10. What is one way that acid rain effects trees?
11. How are historic artifacts being damaged by acid rain?
12. How is human health effected by acidic rain?
13. Name one more negative effect of acid rain.
14. Why is it that acid rain is not a localized environmental concern, but a regional one?
15. Name one thing that can be done to reduce acid rain.
16. What are two things you can do to help reduce acid rain?
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Southern AER is a quarterly publication of the Southeast Regional Climate Center. Funding is provided by a grant from the National Oceanic and Atmospheric Administration.
Internet Resources On Acid Rain