H2S | Hydrogen Sulphide | Sources & Impacts | OIZOM Academy
Channel: Oizom
Date: 06/01/2021

H2S is formed whenever elemental sulfur or sulfur-containing compounds come into contact with organic materials at high temperatures. Continuous or high-level exposure of the H2S can quickly deaden a person’s sense of smell, making the odour of H2S an unreliable indicator of its presence. Hence, other means such as hydrogen sulfide monitoring is a viable solution to provide adequate warning of hazardous exposure. This article covers information on hydrogen sulfide, its sources in the ambient air, permissible levels, health and environmental impact. Additionally, it also highlights possible corrective measures, the need for H2S monitors and different methods of H2S monitoring.

Hydrogen sulfide in Atmosphere
H2S is present naturally in crude petroleum, natural gas, and hot springs. It is released into the atmosphere primarily as gas from volcanoes, geothermal vents, sulfur springs and lakes, salt marshes, and estuaries. Also, bacterial breakdown (anaerobic decay) of organic sulfur compounds also produce H2S.

Conversion of organic matter into H2S
Once released it remains in the atmosphere for about 18 hours before converting to other sulfur oxides. H2S in the air oxidizes to form SO2 which consequently reacts to form sulfate particles. It also contributes to acid rain by dissolving into water vapor to form sulfuric acid. 

Formation of SO2 by oxidation of H2S
Sources
Most of the atmospheric hydrogen sulfide has natural origins (about 90%)  formed under conditions of deficient oxygen, in the presence of organic material and sulfate. Hence, it is one of the major pollutants emitted from sewage and waste-water treatment plants, utility facilities, and sewers. It is also present in compounds such as natural gas and crude petroleum. Anthropogenic activities such as drilling, production, and refining of crude oil and natural gas allow the release of H2S in the atmosphere.

H2S can be formed whenever elemental sulfur or sulfur-containing compounds come into contact with organic materials at high temperatures. In industries, for instance, production of coke, viscose rayon production, wood pulp, etc. emit the gaseous pollutant in the air. Other sources include sulfur extraction processes, tanning, mining, sugar-beet processing, and hot-asphalt paving. 

Health & Environmental Impact of H2S
Health Impact
H2S is both an irritant and as well as a chemical asphyxiant when inhaled affects the oxygen utilization and the central nervous system of the body. It has a detectable odour even at low concentrations, however with continued exposure and at high concentrations, it causes olfactory fatigue i.e. the person loses the ability to smell H2S even if it is present. At very high concentrations, the ability to smell the gas can be lost instantaneously. Its health effects can vary depending on the level and duration of exposure. 

Effects of H2S exposure, effects of hydrogen sulphide exposure
[https://hnhu.org/health-topic/what-is-hydrogen-sulphide-h2s/]
After exposure to H2S, symptoms usually begin immediately. At low levels, symptoms such as irritation of the eyes, nose, and throat occur. H2S does not accumulate in the body. But repeated and prolonged exposures can cause low blood pressure, headache, dizziness, nausea, and vomiting, as well as coughing and difficulty in breathing while higher levels can cause shock, convulsions, coma, and death. 

Environmental Impact
H2S, being somewhat water-soluble, results in the formation of sulfhydric acid (H2SO4), which is corrosive to metals, and contributes to acidic deposition to soil and water. Additionally, it is capable of corroding metals.  

Electrochemical
H2S monitors working on the electrochemical principle are operated based on the diffusion of hydrogen sulfide gas into the sensor which results in the production of electrical signals proportional to the H2S concentration. Therefore, it allows accurate measurement of even low concentrations of H2S, which is essential in H2S monitoring in the ambient air. 

Among all the above principles of H2S monitoring, applications like ambient air monitoring prefer hydrogen sulfide monitors based on electrochemistry. This is because they yield more accurate H2S  concentrations and are inexpensive in comparison with the others.


Real-time monitoring of H2S levels helps in determining the source of the odour as well as formulating an action plan to control odour.