Totally reduced sulphurs are odourous compounds. Examples include:
- Hydrogen sulphide – it has a rotten-egg odour; its odour threshold is 0.5 ppb.
- Methyl mercaptans – these are added to natural gas to give it a distinctive odour.
Total reduced sulphur (TRS) can be created by industrial sources, such as oil refineries, pulp and paper mills, steel mills and sewage treatment facilities. It can also be generated naturally, being released from swamps, bogs and marshy areas.
TRS compounds in small concentrations are not normally considered a health hazard. however, they produce a rotten egg or cooked cabbage-like odour, which is offensive to many people.
Most people can smell TRS compounds at very low levels. So, for affected industrial operations, the challenge is to manage TRS compound materials in such a way so as to avoid the escape of errant odours. With most industrial plant sites having comprehensive odour control programs in place, fugitive emissions of TRS normally last for only a short duration.
Fluorescent technology, similar to the method used for tracking SO2, is applied to continuously monitor TRS compounds in ambient air. An air sample is first drawn through a filter that removes any trace of SO2. In a second step, a high-temperature converter changes the TRS components to SO2, with the resulting concentration measured by fluorescence.