TVOC | Total Volatile Organic Compounds TVOC | Sources, impact and monitoring | OIZOM Academy
Channel: Oizom
Date: 2021-01-06

Total Volatile Organic Compounds (TVOC) are a group of compounds containing carbon that have a high vapour pressure present in the air. There are abundant VOC emitted from everyday activities among which some are colourless and some odourless and some are toxic. TVOC monitoring is an efficient way to detect exposure to toxic VOCs. This article covers information on total volatile organic compounds, their sources in the ambient air, characteristics, health and environmental impact, possible corrective measures, need for TVOC monitors as well as different methods of TVOC monitoring.

There are a large number of VOCs present in the environment making it difficult to continuously monitor them simultaneously. Hence, a common term TVOC (Total Volatile Organic Carbon) is used representing the total concentration of VOCs present in the air. Such a common term of measurement makes it easier to determine the overall presence of VOC and is cheaper than measuring individual VOCs.

TVOC in Atmosphere
We are in continuous contact with several products that contain and/or emit VOCs like disinfectants, paints and varnishes, solvents, semiconducting materials, rubber, vehicle exhaust, fuel, ink, adhesives, etc. Each VOC has its characteristic signature. For example, due to combustion, vehicle exhaust emits ethene while broadleaf trees emit isoprene. Different VOCs have different reaction rates and hence, have a large range of transport distances ones emitted. VOCs that have low creativity remain in the atmosphere for large durations of time are known as Persistent Organic Pollutants (POPs) and some VOCs are known as Hazardous Air Pollutants (HAPs) because of their toxicity.

Health Impact
Not all VOCs are harmful to human health, its impact majorly depends on the chemical composition, amount of exposure, and its dilution. Benzene, formaldehyde, diesel exhaust, styrene, and perchloroethylene are known or suspected carcinogens and their exposure can pose serious health risks. Toluene, ethylbenzene, o-, m-, and p- xylenes have been found to develop adverse health impacts on respiratory and neurological effects.

Environmental Impact
VOCs result in the formation of secondary air pollutants such as ozone, smog and fine particulate matter which in turn have their own adverse effects on human health and environment. 

VOCs in the atmosphere react with another primary pollutant NOx, in the presence of sunlight to form ozone (O3) and fine particulate matter (PM2.5). The accumulation of O3, PM2.5, and other air pollutants in the atmosphere results and smog formation and visibility reduction.


Photoionisation detection (PID)
TVOC monitor working on the principle of PID uses high-energy photons to detect the VOC levels. The air sample drawn into the TVOC monitor is exposed to UV light of a specific output that excites the VOC molecules present in the air sample. The molecules become electrically charged as it ionizes everything that has an ionization energy less than or equal to the UV lamp output. The ions produce an electric current proportional to the concentration of TVOC and are measured by the detector.

Reasons why TVOC monitoring is important
VOCs are a group of organic compounds that are easily vaporized. There are abundant VOC emitted from everyday activities among which some are colorless and some odorless. 
Exposure to toxic VOCs may lead to severe health issues such as chronic respiratory diseases, damage to the kidney, liver, and/or central nervous system, and even cause cancer. 
VOCs in the atmosphere are major contributors to the formation of secondary air pollutants ground level ozone, fine particulate matter (PM2.5), and smog which adversely affect human health and the environment. 
TVOC monitoring is an efficient way to detect exposure to toxic VOCs.
Real-time monitoring of TVOC levels helps in determining their source as well as formulating an action plan to control VOC emissions.