Sulphur oxides (SOx)
Gases formed principally by the burning of fossil fuels containing sulphur, such as coal and oil. Sulphur oxides such as sulphur dioxide (SO2) and sulphates are pollutants that contribute to the formation of smog. Since SO2 dissolves in water vapour to form acid and interacts with other gases in the atmosphere to form sulphates and other products that can be harmful to the environment, ambient air-quality standards have been adopted in many areas to regulate sulphur oxides emissions.
* see also nitrogen oxide