Acid Rain Acid rain forms when sulfur and nitrogen dioxides combine with moisture in the atmosphere to produce rain, snow, or another kind of precipitation. This kind of pollution may also be suspended in fog or deposited in a dry form. Acid rain is most common in North America and Europe. Acid rain has also been detected in other areas of the world such as tropical rain forests of Africa. Canada has placed limitations on the sulfur emissions. The United States has not, so the emissions may still drift into Canada. The acid rain cycle begins with hundreds of power plants burning millions of tons of coal. Bur