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Sulfur dioxide (SO₂) is a colorless, toxic gas with a sharp, pungent odor reminiscent of burning matches. It is highly soluble in water, forming sulfurous acid (H₂SO₃), and is both naturally occurring and human-generated. Major natural sources include volcanic eruptions, while human activities such as the combustion of coal, oil, and gasoline, as well as metal smelting and other industrial processes, are significant contributors to atmospheric SO₂ emissions.

Chemically, sulfur dioxide consists of one sulfur atom covalently bonded to two oxygen atoms, with a molecular weight of approximately 64.07 g/mol. It has a melting point of -72.7°C and a boiling point of -10°C, making it a gas under standard conditions. SO₂ is denser than air, with a gas density of about 2.93 g/L at 0°C and 1 atm, and is easily liquefied under pressure or at low temperatures. It is stable when dry but becomes corrosive in the presence of moisture.

SO₂ is highly reactive and plays an important role in atmospheric chemistry. In the atmosphere, it can oxidize to form sulfur trioxide (SO₃), which subsequently reacts with water to produce sulfuric acid (H₂SO₄), a major component of acid rain. This transformation contributes significantly to environmental pollution and ecosystem damage.

Industrially, sulfur dioxide is crucial for the production of sulfuric acid, one of the most widely produced chemicals globally. It is also used as a bleaching agent in paper and textile manufacturing, a preservative in food and beverages (notably in winemaking and dried fruits), a disinfectant, and a reducing agent in various chemical processes. In metallurgy, SO₂ is used in ore processing and metal extraction.

References

1. National Aeronautics and Space Administration (NASA), NW-2011-10-093-GSFC, Sulfur Dioxide Poster.
2. United States Environmental Protection Agency (EPA), Sulfur Dioxide (SO2) Pollution, Entry updated on 10^th Jan 2025.
3. Wikipedia, Sulfur Dioxide, Entry edited on 22^nd May 2025.
4. Chemical Book > CAS Database List > Sulfur Dioxide, Entry updated on 27^_th Jan 2025.
5. Black Ling, 9^th Jun 2024, Sulfur Dioxide: Properties, Uses, and Environmental Impact, ALTOMERGE.
6. cK-12 > All Subjects > CBSE Science > Oxygen and its compounds > Question > What are the physical properties of sulphur dioxide? (Acccessed 17^th Jul 2025)
7. American Chemical Society (ACS), 28^th Aug 2023, Molecule of the Week Archive > Sulfur Dioxide.