Chemical changes to rain start with the emission of pollutants in the air. The majority of these pollutants are from the burning of fossil fuels such as coal and gasoline. Power plants release the majority of sulfur oxides. The burning of fossils fuels results in the emission of nitrogen oxides. Sulfur oxides, nitrogen oxides, and carbon oxides are released into the atmosphere and mix with water, oxygen, and other chemicals to produce acidic pollutants. When the pollutants change the pH of precipitation, it is known as acid rain. Acid rain can have harmful effects on plants and animals (especially those that inhabit aquatic environments), as well as infostructures. Statues made of soft limestone can be deteriorated over time by acid rain.