Nepedia
Back to Discover
Advanced Reader
⚛️

Sulfur dioxide

physical science Maturity 11-13 Next article →

Sulfur dioxide is a colorless gas with a sharp, pungent odor. You might recognize this smell from a burnt match. In chemistry, it is a compound with the formula SO2. It is made of one sulfur atom and two oxygen atoms. This molecule has a bent shape known as C2v symmetry. It is a very important substance in both chemistry and planetary science. It can be a useful tool for humans or a natural part of a planet's atmosphere.

Sulfur-dioxide-resonance-2D
Sulfur-dioxide-resonance-2D

The way sulfur dioxide forms depends on the process involved. One common method is the combustion of elemental sulfur. When sulfur burns in oxygen, it releases a significant amount of heat. This reaction is exothermic, meaning it gives off energy. To help this process, liquid sulfur is often sprayed through a nozzle to create fine drops. This increases the surface area for the reaction. The heat produced is so large that it can be used to generate steam. This steam can then be turned into electricity.

Other industrial methods also produce this gas. For example, workers can roast sulfide ores like pyrite or cinnabar in the air. This process also releases sulfur dioxide. It can even be a byproduct when making calcium silicate cement. In this case, calcium sulfate is heated with coke and sand. This chemical process was used extensively in Whitehaven, England, until the 1970s. In laboratories, scientists can also create the gas by reacting hot concentrated sulfuric acid with copper.

Volcanic injection
Volcanic injection

Nature produces sulfur dioxide on a massive scale through volcanic activity. Large eruptions can release millions of tons of the gas at once.

20180519 USGS Leilani Estates Hawaii Volcanic EruptionDSC 0411 medium
20180519 USGS Leilani Estates Hawaii Volcanic EruptionDSC 0411 medium

This gas is found all over our solar system in different amounts. On Earth, it exists in very small amounts, about 15 parts per billion. On the moon Io, it is much more common, making up 90% of its atmosphere. This causes the moon to have beautiful blue auroral glows.

Io Aurorae color
Io Aurorae color

On Venus, it is the third-most abundant gas at 150 parts per million. There, it reacts with water to form clouds of sulfurous acid.

Space telescopes have even found this gas on distant worlds. The James Webb Space Telescope detected sulfur dioxide on the exoplanet WASP-39b. On that planet, the gas is formed through photochemistry. This means light from the star helps create the chemical. On other moons like Europa, Ganymede, and Callisto, it is thought to exist as ice. It may also be found in liquid form within their crusts and mantles. These findings help scientists understand the different cycles of sulfur across the universe.

Humans use sulfur dioxide for many practical purposes. Its most dominant use is as an intermediate in making sulfuric acid. This is done through the contact process. In the United States in 1979, 23.6 million metric tons were used for acid production. This was much higher than the 150,000 metric tons used for other purposes. It is also a helpful preservative for food. In Europe, it is used to keep dried fruits like figs and apricots colorful. It prevents rotting by acting as an antimicrobial agent.

Cheletropic reaction of butadiene with SO2
Cheletropic reaction of butadiene with SO2

Winemakers have used this gas since the time of the Romans. They discovered that burning sulfur candles in empty wine vessels kept the wine fresh. It acts as an antioxidant and an antibiotic. This stops the wine from browning or turning into vinegar due to bacteria. In the wine, it exists in different forms like molecular SO2 or bisulfite ions. The amount used is measured in parts per million. For example, the EU allows up to 210 ppm in white wine. It is also used to clean winery equipment using a mixture of water and citric acid.

Beyond food and industry, sulfur dioxide has unique chemical behaviors. It is a mild reducing agent, which means it can help change other substances. In a lab, it can turn moist litmus paper pink and then white. This happens because it is acidic and also has a bleaching effect. It can also be used in the petrochemical industry. Specifically, it is used to make sulfolane, which is an important solvent. This makes sulfur dioxide a vital part of many different scientific and industrial systems.

693 words

Where will your curiosity go next?

Keep exploring at your chosen reading level.

🖼️ Images & Media (12)
File:Sulfur-dioxide-resonance-2D.svg
Sulfur-dioxide-resonance-2D.svg
File:Io Aurorae color.jpg
Io Aurorae color.jpg
03. Горење на сулфур во атмосфера од кислород.webm
File:Cheletropic reaction of butadiene with SO2.svg
Cheletropic reaction of butadiene with SO2.svg
File:Preparation of m-trifluoromethylbenzenesulfonyl chloride.svg
Preparation of...
File:20180519 USGS Leilani Estates Hawaii Volcanic EruptionDSC 0411 medium.jpg
20180519 USGS Leilani Estates Hawaii...
File:Volcanic injection.svg
Volcanic injection.svg
File:Acid rain woods1.JPG
Acid rain woods1.JPG
File:Estimates of past and future SO2 global anthropogenic emissions.png
Estimates of past and future SO2 global...
File:Global sulphur dioxide (SO₂) emissions by world region, OWID.svg
Global sulphur dioxide (SO₂) emissions by...
File:Physical Drivers of climate change.svg
Physical Drivers of climate change.svg
File:SPICE SRM overview.jpg
SPICE SRM overview.jpg
More to explore

✨ What else?

Related topics you might enjoy

🔬 Go deeper

More advanced topics to explore

🪜 Step back

Simpler topics to build understanding

What is Nepedia?

A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.