Acid Rain

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 are brought to Earth in what is called acid rain.

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

The effects of acid rain can be devastating to many forms of life, including human life. Its effects can be most vividly seen, however, in lakes, rivers, and streams and on vegetation. 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.

The threat posed by acid rain is not limited by geographic boundaries, for prevailing 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, including the cathedrals of Europe and the

Colosseum in Rome, have shown signs of deterioration caused by acid rain.

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 and 14 the most basic or alkaline. A solution of distilled water containing neither acids nor alkalies, or bases, is designated 7, or neutral. If the pH level of rain falls below 5.5, the rain is considered acidic. Rainfalls in the eastern United States and in Western Europe often range