Sulfur makes up 3 percent of Earth's crust, and the oceans, air, sulfur hot springs and human digestive system are all sources of sulfur. As of 2014, the petroleum refining industry produces most of the world's supply of sulfur. Petroleum refining produces more sulfur than the market demands.
Sulfur is the 10th most abundant element in the universe. It is a component of many minerals, including iron pyrite, gypsum and galena. Elemental sulfur exists in two crystalline forms and one noncrystalline form.
Removing sulfur from petroleum protects the environment from the release of sulfur compounds into the atmosphere. Most of this sulfur is used in the production of sulfuric acid. Manufacturers use sulfuric acid in the production of fertilizer and lead-acid batteries. As of 2014, scientists are looking for ways to make use of the 10 million tons of excess sulfur produced annually. Heated sulfur forms a polymer that researchers believe has the potential of serving as the backbone for plastics.
Elemental sulfur is odorless; however, many sulfur compounds have an offensive odor. Sulfur dioxide has a rotten egg smell that is sometimes associated with catalytic converters on automobiles. Bacteria in the human gut release odorous compounds responsible for the odorous smell of intestinal gas.