Sulfur is required by all organisms because it is critical in the production of proteins and lignin. Most of Earth’s sulfur supply is locked up in rocks on land and as sulfate salts in deep-sea sediments, but sulfur moves to the atmosphere in a variety of ways. Roughly 10–20 percent of atmospheric sulfur is produced in volcanic eruptions. In terrestrial systems, when sulfur in the soil comes in contact with atmospheric oxygen, it is converted to sulfate salts, which can be taken up by plants and eventually incorporated into their tissue. This sulfur ultimately is returned to the atmosphere as H₂S via microbial decomposition. In marine systems, many phytoplankton and seaweeds manufacture large quantities of a sulfur-containing compound (dimethylsulfoniopropionate, or DMSP) to maintain their salt and water balance. When broken down, DMSP releases dimethyl sulfide (CH₃SCH₃), the principal odorant of rotting seaweed. Because the quantities of phytoplankton in the oceans are enormous, dimethyl sulfide production accounts for about half of the biotic component of the global sulfur cycle.

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Atmospheric sulfur exists in gaseous and particulate forms and plays an important role in global climate. Cloud formation is dependent on small particles around which water can condense. Dimethyl sulfide is a major component of such particles, so increases in atmospheric sulfur concentrations increase cloud cover and reduce the amount of incoming solar radiation, affecting Earth’s temperature. In addition, SO₂ and NO₂ produced by humans from the burning of coal and oil react with water molecules in the atmosphere to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃), respectively. These acids can travel hundreds of kilometers in the atmosphere before they are released as acid rain. Acid rain can damage forests and lakes, affecting the food webs they support. Restriction on the emissions of sulfur in North America and Europe has resulted in significant reductions in acid rain. Research shows that once acidity is reduced, forest and aquatic systems can quickly recover. Acid rain remains a problem in some countries such as China and India, where rapid industrialization and the lack of restrictions create high sulfur emissions.