Acid Rain

When fossil fuels such as coal, gasoline, and fuel oils are burned, they emit oxides of sulfur, carbon, and nitrogen into the air. These oxides combine with moisture in the air to form sulfuric acid, carbonic acid, and nitric acid. When it rains or snows, these acids fall on the earth in what is called acid rain.

During the 20th century, the acidity of the air and acid rain have. come to be recognized as leading threats to the stability and quality of Earth's environment. Most of this acidity is produced in the industrialized nations of the Northern Hemisphere.—the United States, Canada, Japan, and many countries of Europe.

The effects of acid rain can be very destructive to many forms of life, including human life. Its effects can be most vividly seen, however, in lakes, rivers, and streams. Acidity in water kills virtually all life forms. By the early 1990s, tens of thousands of lakes had been destroyed by acid rain. The problem has been most severe in Norway, Sweden, and Canada.

Scientists use what is called the PH factor to measure the acidity or alkalinity of liquid solutions. On a scale from 0 to 14, the number 0 represents the highest level of acid. 14 represents the most basic or alkaline. Rainfalls in the eastern United States and in Western Europe often have a PH factor ranging from 4.5 to 4.0.

The threat posed by acid rain is not limited by geographic boundaries. Winds carry the pollutants around the globe. For example, much research supports the conclusion that pollution from coal-powered electric generating stations in the midwestern United States is the ultimate cause of the severe acid-rain problem in eastern Canada and the northeastern United States. Nor are the destructive effects of acid rain limited to the natural environment. Structures made of stone, metal, and cement have also been damaged or destroyed. Some of the world's great monuments have shown signs of damage. This damage is probably caused by acid rain.

The cost of antipollution equipment such as burners, filters, and chemical and washing devices is great. However, the cost in damage to the environment and human life is estimated to be much greater because the damage caused by acid rain may be irreversible. Although preventive measures are being taken, up to 500,000 lakes in North America may be destroyed before the end of the 20th century.