The quality of Earth's atmosphere is a significant social issue, not only in the United States, but in every industrialized nation on the planet. One issue that has captured the attention of governments and ordinary citizens is the effects of acid rain on the environment. Acid rain has also been the topic of some commercially produced STS units, and physical science and Earth science teachers have easily incorporated an STS acid rain module into their ongoing curriculum.
Acid Rain Issue
Acid Rain, more accurately called acid precipitation, is rain, snow or fog that contains a significant amount of sulfuric acid or nitric acid. The primary cause of acid rain is the combustion of coal and oil, processes in which large quantities of sulfur dioxide and nitrogen oxides are released into the atmosphere. Once in the atmosphere, sulfates and nitrates combine with moisture to form sulfuric acid and nitric acid. A small percentage of acid precipitation results from natural causes, such as volcanic activity. However, approximately 90 percent is caused by humans.
Effects of Acid Rain. Acid rain is harmful to human health, increasing the rate of infant mortality and reducing proper lung functioning in many Americans. Research has implicated airborne sulfates in at least 50,000 premature deaths each year as many lives as are lost in automobile accidents. For people with asthma, even low levels of sulfur pollution can cause serious lung damage in a matter of minutes.
Acid rain also causes acidification of rivers and lakes, a process disruptive to aquatic ecosystems. When acidity levels become too high, fish can no longer reproduce and soon die out. High acidity levels leach heavy metals, such as mercury and lead, from lake and river beds.These metals often end up in the tissues of fish, making them toxic to human consumption. Acid levels in rivers and lakes are highest in the spring when snowpacks melt and release high concentrations of pollutants. Unfortunately, this happens at a crucial time in the lives of fish spawning season.
Damage to tree foliage and degraded soil quality are other effects of acid rain. About half of West Germany's forests show signs of damage caused by high levels of acidity in rain and fog. In Canada and northern New England acid rain has been linked to large scale damage to maple trees, threatening the maple syrup industry. Since factories are often equipped with tall smokestacks that send sulfur dioxide and nitrogen oxides high into the atmosphere, they may be carried by wind streams for hundreds of miles. Thus, one country will often receive anothers acid rain. Half of Canada's acid rain originates in the United States.
Numerous buildings and construction materials are also subject to damage caused by acid rain, making the problem directly economic as well as environmental. A draft EPA study estimated the damage to building materials in 17 northeastern and midwestern states to run as high as $6 billion annually. Not even our cultural history is safe, as thousands of statues and monuments are crumbling and corroding. Some of the hardest hit include the Statue of Liberty and the Gettysburg Battlefield.
STS Actions.
• Ask students to make a diagram showing how they think acid rain is formed and how it effects the environment. Give the students the following list of terms that they may use to aid in the creation of the diagram: coal, power plant, smokestacks, water vapor, rain, acid, combustion products, trees, rivers. Use the results to identify student misconceptions.
• Collect rain samples over a sustainable period and determine the pH using cabbage juice (boil four or five red cabbage leaves in two quarts of water) as an indicator. The purple juice turns pink in acid solutions, and green in basic solutions. Students can also collaborate with counterparts in other schools to gather data on acid rain over a larger area.
• Participate in an Internet-based project in which students monitor the acidity of rain in their local area. The Internet is used to share data and discuss results and implications. See Eco-Connections.