Sulfur dioxide is a colourless gas with a pungent, irritating odour similar to burning sulfur. It is a colourless liquid below -10 deg C. Sulfur dioxide will not burn. It is a COMPRESSED GAS. Cylinders or tanks may rupture and explode if heated. It is VERY TOXIC and may be fatal if inhaled. Sulfur dioxide is also extremely irritating to eyes and respiratory tract. It causes lung injury and these effects may be delayed. It may also cause frostbite.

Its major use is a captive intermediate in the production of sulfuric acid. In the pulp and paper industry, sulfur dioxide is used to produce other chemicals such as chlorine dioxide and sodium hyposulfite and is also used in the bleaching of pulp. In food processing, sulfur dioxide is used for fumigating, preserving, bleaching and steeping. It is also used to reduce residual chlorine in potable water, treated sewage and industrial effluent, as an oxygen scavenger, a selective extraction solvent and as a catalyst in chemical processes. In the presence of a catalyst (e.g. nitrogen compounds), sulfur dioxide can be oxidized to sulfuric acid. Occurs as a by-product during the burning (combustion) of sulfur containing organic compounds (e.g. coal). A common component of air pollution, it is a major contributor to acid rain.

Available as a liquefied compressed gas. The anhydrous grade has a minimum purity of 99.98%.

Sulfur dioxide is also known as bisulfite, SO₂, sulfurous acid anhydride, sulfurous anhydride, sulfurous oxide, sulfur oxide, sulphur dioxide, and dioxide de soufre.

Some names are non-specific because they can refer to several forms (e.g. isomers) of the same chemical or they may refer to different chemicals. For example, "bisulfite" can also mean sodium bisulfite and sulfur oxide can mean sulfur trioxide.

Its CAS Registry Number is 7446-09-5. This number is assigned by the Chemical Abstracts Service (CAS) in the United States and is used as a unique identifier number world-wide.