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
from 4.5 to 4.0.
Although the cost of such antipollution equipment as burners, filters, and
chemical and washing devices is great, the cost in damage to the environment and
human life is estimated to be much greater because the damage may be
irreversible. Although preventative measures are being taken, up to 500,000
lakes in North America and more than 4 billion cubic feet (118 million cubic
meters) of timber in Europe may be destroyed before the end of the 20th century.

Sebastian Kovacs [email protected]