Sulfur dioxide is a colorless gas with the chemical formula SO₂, consisting of one sulfur atom double-bonded to two oxygen atoms in a bent molecular structure. Known since ancient times when sulfur was burned in religious ceremonies, SO₂ was first studied scientifically by Joseph Priestley and Antoine Lavoisier in the 1770s, who recognized it as a distinct compound responsible for the choking fumes of burning sulfur. With its sharp, suffocating odor reminiscent of struck matches, sulfur dioxide serves as both a major air pollutant from fossil fuel combustion – causing acid rain and respiratory problems – and an essential industrial chemical used in winemaking, food preservation, and manufacturing sulfuric acid. This dual nature as both environmental villain and industrial workhorse makes SO₂ one of the most carefully regulated yet widely used gases, with global emissions exceeding 100 million tons annually despite decades of pollution controls.

Find a review of the 50 most important industrial gases here.

20 Fun Facts About Sulfur Dioxide

Beyond the basics above, what else should we know about Sulfur Dioxide? Check out the 20 fun facts below!

1. SO₂ molecules are bent at 119.5°, making them polar and highly soluble in water to form sulfurous acid instantly.
2. Wine contains 10-350 ppm SO₂ as a preservative, with “contains sulfites” required on labels above 10 ppm.
3. The gas liquefies at -10°C (14°F) under atmospheric pressure, making it one of the easiest gases to liquefy.
4. Volcanic eruptions inject millions of tons of SO₂ into the stratosphere, cooling Earth by 0.5°C for 1-3 years.
5. The compound glows blue-green when excited electrically, used in some specialty discharge lamps for UV generation.
6. Ancient Romans burned sulfur candles to bleach togas white and fumigate homes, unknowingly using SO₂.
7. SO₂ detectors in spacecraft monitor for electrical fires, as burning insulation produces distinctive sulfur dioxide signatures.
8. The molecule vibrates at 1,151 and 1,361 cm⁻¹, allowing satellites to map volcanic plumes from space.
9. Dried fruits contain up to 2,000 ppm SO₂ to prevent browning, 10 times more than wine.
10. London’s “Great Smog” of 1952 killed 4,000 people in four days from SO₂ combining with fog to form sulfuric acid.
11. The gas dissolves copper at room temperature, requiring special stainless steel piping in industrial applications.
12. SO₂ snow falls on Jupiter’s moon Io near volcanic vents, creating yellow-white frost at -160°C.
13. Paper mills use 20 million tons of SO₂ annually in the sulfite pulping process to dissolve lignin from wood.
14. The compound kills bacteria 1,000 times more effectively at wine’s acidic pH than at neutral pH.
15. China emits 20 million tons of SO₂ yearly, visible from space as a brown cloud stretching across the Pacific.
16. Sulfur dioxide forms deep eutectic solvents with some salts, creating room-temperature ionic liquids for green chemistry.
17. The Lewis structure has sulfur exceeding the octet rule, using d-orbitals that don’t actually participate significantly.
18. SO₂ levels in ice cores reveal ancient volcanic eruptions, including Tambora in 1815 that caused the “year without summer.”
19. Astronauts can smell SO₂ on their suits after spacewalks from reactions between atomic oxygen and trace sulfur.
20. The gas refrigerated early ice cream parlors as “R-764” until ammonia systems proved safer in the 1920s.

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