Sulphur dioxide
Air quality sulfur dioxide SO₂
Sulphur dioxide, SO₂, is an air pollutant from sulphur-containing fuels and other sources. It can affect the airways and contribute to particulate matter.
Where the gas comes from
Burning coal or oil containing sulphur can release sulphur dioxide. Industrial processes and natural sources such as volcanoes also emit it. The gas is colourless and has a sharp smell at higher concentrations.
What it becomes in the air
SO₂ dissolves in water and can react further to form sulphate. The resulting compounds contribute to acidification and particle formation. Sulphur dioxide therefore matters both as a gas and as a precursor of some particulate matter.
How concentration is reported
The usual unit is micrograms per cubic metre (µg/m³). The averaging period matters: a short peak differs from elevated exposure over several hours. Smell cannot replace measurement; “I cannot smell anything” is not a concentration reading.
How weather affects it
Wind can dilute pollution or carry it from distant sources. Stable air can restrict mixing, while precipitation removes soluble substances. Models represent these processes on a grid. Checked measurements near a particular road or source may show different conditions.