Air pollution is caused by a number of both human and nature-based sources. The first primary source is emissions from planes, automobiles, ships, power plants, and other human activities that involve burning fossil fuels. The second primary source is tobacco smoking and the past use of products containing chlorofluorocarbons, such as hair spray and other aerosols. The third primary source is pesticides, which may be stirred up and rise into the air during windstorms or the application process. Finally, nature is a frequent cause of pollutants in the air. Gasses such as methane and ammonia are regularly released from the manure of livestock and swampy regions. Wildfires and volcanic eruptions emit pollutants into the air. Other common causes of indoor pollution include lead, the burning of kerosene, wood-burning stoves or fire places, tobacco products, dust, cleaning chemicals, building materials, furniture, people, pets, mold caused by excess moisture and more.