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Why to measure TVOC or indoor air quality?

Volatile Organic Compounds or VOCs are organic chemicals that become a gas at room temperature. They are the main origin of air pollution at ground level. A common term used when measuring and eliminating VOCs is “Total VOC” or TVOC. TVOC stands for the total concentration of multiple VOCs that are simultaneously present in the air.
The human contribution to indoor air pollutants has often been associated with CO2, which is commonly used as an indicator of insufficient ventilation in closed spaces. However, CO2 is far from the only pollutant. An often-overlooked group of pollutants are Volatile Organic Compounds (VOCs). The most common compounds are benzene, ethylene glycol, formaldehyde, methylene chloride, tetrachloroethylene, toluene, xylene, and 1,3-butadiene.
Limit values for VOCs
There will always be some VOCs present in the air, both outside and inside. As is often the case, the dose makes the poison. Concentrations of VOC in indoor air are usually 2 to 5 times greater than in outdoor air and indoor air can contain up to 1,000 times greater concentrations, depending on what the room is used for. VOC exposure risk is greatest in buildings that are between 0 and 2 years old. 

The organization Indoor Environmental Quality recommends a limit value of 500 ppb TVOC. They base their recommendation on reports from the USEPA, Australian NHMRC, and a consensus of researchers and indoor environment rating schemes.

Sources of VOCs
Sources of indoor VOCs vary. VOCs can come from outside, from humans, and from manufactured everyday products. Outside VOCs come from plants and pesticides. If you live or work in or near industrial environments, certain VOCs can have a high local concentration. When humans breathe, they emit VOCs as well. When many humans are together in a room, the emission of VOCs can rapidly increase. Everyday products that emit VOCs include paints, disinfectants, and air fresheners. As there are different sources of VOCs, the exact concentrations and common types of compounds depend on the type of room. In kitchens, the major source of TVOCs will come from cooking and detergents. In garages, it will come from exhaust products, automotive fluids, and pesticides. In bedrooms, living rooms and offices, it will come from building materials, cleaning products, and humans.
Especially vulnerable locations for high VOC concentrations are hospitals and nursing homes. In these environments, chemicals that release VOCs are often used for the necessary cleaning, disinfection, and generally heightened hygiene.

Effects of VOCs
VOCs are known to cause eye, nose and throat irritations, headache, drowsiness, dizziness, nausea, difficulty concentrating and fatigue. Continual and long-term exposure to TVOCs has been linked to various cancers. This is especially the case when it comes to formaldehyde, which can be prevalent in bedrooms, offices and living rooms. In children, VOCs have been linked to the development of allergies.
Apart from the health risks, VOCs also limit personal comfort. Some VOCs, such as toluene, are irritants. Even though detergents can be a major source of VOCs, a high VOC level can negatively affect the perception of cleanliness and release bad odours.

Applications of TVOC-based ventilation
TVOC sensors have an increased selectivity to hydrogen (H2). In indoor environments, the H2 concentration is expected to correlate well with the CO2 concentrations, as human breath contains significant concentrations of both CO2 (4 %) and H2 (10 ppm). Furthermore, humans are a major source of CO2 and H2 in typical indoor environments. This makes it possible to distinguish the influence of human presence from other contaminants and control the ventilation system based on the occupation of a space.
Ventilation in function of TVOC level is interesting in environments where indoor air quality needs to be optimised on a continuous base, such as living rooms, office buildings, certain industrial environments, etc.
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