Cl2 | Chlorine | Sources and Impacts | OIZOM Academy
Channel: Oizom
Date: 06/01/2021

Elemental chlorine is a highly reactive, greenish yellow gas. It has a suffocating, irritating, pungent bleach like odour that is detectable at low concentrations (above 0.3 – 0.5 ppm). Continuous or high-level exposure of the Cl2 can quickly deaden a person’s sense of smell, making the odour of Cl2 an unreliable indicator of its presence. Hence, other means such as chlorine monitoring is a viable solution to provide adequate warning of hazardous exposure. This article covers information on chlorine gas, its sources in the ambient air, permissible levels, health and environmental impact, possible corrective measures, need for chlorine monitors as well as different methods of H2S monitoring.


Chlorine in the Atmosphere
Elemental chlorine is rarely present itself in nature due to its high reactivity. It can be formed from atmospheric reactions of chlorine-containing compounds with NO2 and through oxidation of chlorides in presence of strong oxidants in the atmosphere such as ozone. 

Once released, it rapidly combines with other chemicals/compounds in the atmosphere to form secondary compounds instead of remaining in pure elemental state. Chlorine dissolves in the water and reacts to form chloride salts and chlorinated organic chemicals such as sodium chloride (NaCl, common salt), sodium hypochlorite (bleach), chloroform, etc. 

Sources of Chlorine
Chlorine gas is commonly used 

as household cleaner and disinfectant
oxidizing agents in water treatment to disinfect drinking water 
as a disinfectant in industrial applications such as food processing, pulp and paper mill and water cooling systems, etc.
in the bleaching process in pulp and paper mills and ink removal from recycled paper
in the manufacturing of many products such as paper, antiseptic, insecticides, paints, petroleum products, textiles, medicines, etc. 

Health impact
Chlorine is majorly toxic due to its oxidizing and corrosive properties. When in contact with Cl2 gas, the hydrogen in moist tissue splits from water. Thus, producing hydrogen chloride (HCl) which damages tissue. It also forms hypochlorous acid (HOCl) that penetrates cells in the body and destroys the cell structures by reacting with the cytoplasmic proteins. 


Environmental Impact
Chlorine gas does not have a direct impact on the environment. However, it contributes to environmental problems such as ozone layer depletion, global warming and acid rain. Cl2 in the atmosphere destroys the ozone molecules as shown below.

Formation of chlorine gas
https://bodell.mtchs.org/OnlineBio/BIOCD/text/chapter36/
Additionally, chlorine gas rapidly combines with other compounds to form chemicals such as dioxins. These dioxins pollute water, contaminating fish which is then consumed by larger animals and humans. 

Electrochemical method for Chlorine monitoring
Chlorine monitors working on the electrochemical principle are operated based on the diffusion of Cl2 gas into the respective sensor which results in the production of electrical signals proportional to the chlorine concentration. It allows accurate measurement of even low concentrations of Cl2, which is essential in chlorine monitoring for the ambient air. 


5 Reasons why Cl2 monitoring is important
Cl2 is highly reactive, greenish yellow gas that has a suffocating, irritating, pungent bleach like odour and can accumulate in enclosed, poorly ventilated, and low lying areas.
Cl2 reacts with moisture in the tissues of the human body and forms toxic products such as hydrogen chloride (HCl) and hypochlorous acid (HOCl) that causes damage to tissues and cell structure of the body. 
Exposure to chlorine gas may cause irritation to eyes, skin, and respiratory tract, coughing, wheezing. accumulation of fluid in lungs, etc and may even lead to death. It also contributes to ozone layer depletion. 
Continuous or high-level exposure of the Cl2 can quickly deaden a person’s sense of smell, making odour of Cl2 an unreliable indicator of its presence. Hence, other means such as the use of Cl2 monitors is a viable solution to provide adequate warnings of hazardous exposure.
Real-time Cl2 monitoring helps in determining the source of odour as well as formulating an action plan to control emission of chlorine.