Acid rain can be caused by many things. Industrial emissions from factories and power plants that burn fuels such as natural gas, coal or oil, emit smoke that gives off oxides of sulfur and nitrogen is one cause. Another cause is vehicles (e.g. cars, buses) that burn gasoline and diesel. The exhaust emitted by burning these fuels contains sulfur dioxide, an oxide of sulfur. Also, vehicles that have gas engines will produce oxides of nitrogen, another cause of acid rain. One other cause is home fires giving off smoke that contains sulfur dioxide. Some fairly minor causes are natural causes which are volcanoes, swamps and rotting plants giving off sulfur dioxide. Natural causes only account for 10% of the pollution causing acid rain.
Pollutants from a source of pollution drift up to the atmosphere. Once in the atmosphere, the pollutants combine with moisture to form acid rain. The acid rain is collected in a cloud and will be released when it rains. The pollutants used in this example are the two pollutants that cause acid rain: oxides of sulfur and oxides of nitrogen.