Published on November 25, 2014
Natural: forest fires, dust storm Unnatural : man-made; coal, wood and other fuels used in cars, homes, and factories for energy Industries burn large quantities of fuel. Burning coal and petroleum releases poisonous gases into the air. Airplanes, boats, and cars burn petroleum, releasing carbon monoxide and carbon dioxide. The waste in landfills releases methane. Animals emit carbon dioxide when they breathe, and volcanoes release sulfur oxide.