Hydrogen sulfide (H₂S) is a naturally occurring chemical compound composed of one sulfur atom covalently single bonded to two hydrogen atoms. It is a toxic, flammable, and colorless gas known for its rotten egg smell. Hydrogen sulfide is found in volcanoes and some hot springs. It is an essential part of the sulfur cycle, produced in oxygen-poor environments, such as swamps, during microbial organic matter decomposition. Other bacteria break down hydrogen sulfide, for example, producing sulfur or sulfate when using it for fuel.

Hydrogen sulfide is a significant issue from industrial activities. It can result from processes in petroleum refineries, sewage treatment plants, tanneries, and paper mills. It poses a particular danger as its scent can be detected at low levels, but evades detection in higher, potentially toxic, concentrations as it deadens sense of smell. Elevated hydrogen sulfide can also trigger unwanted effects such as corrosion of certain contacted materials (e.g. metal pipes) or adverse environmental impacts such as acid rain. Due to these dangers, precisely measuring both natural and anthropogenic hydrogen sulfide sources is a critical practice to understanding its effects.

Picarro has designed and produced a gas concentration analyzer that precisely measures hydrogen sulfide for laboratory and field studies.