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