The term “VOC” or volatile organic compounds originated from the English words Volatile Organic Compounds.
\n(Volatile = fleeting, thus in gaseous state at room temperature)
\nPeople began to take a deeper interest in air quality only in the second half of the last century, when more and more people started to spend longer periods indoors. Unpleasant feelings such as fatigue, drowsiness, headaches, and even nausea or various allergy symptoms began to manifest in them – all largely due to low air quality.
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\nWhether we like it or not, we ourselves have the most negative impact on indoor air quality – through our own breathing process or even increased metabolic activity associated with intense physical activity in the given space.
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\nThe human body thus releases not only the well-known carbon dioxide through breath, sweat, skin transpiration, and similar means, but also other substances such as ammonia, acetone, ethylene, methane, and many other types of volatile organic compounds that are produced during the digestion of organic food. All of this depends on age, dietary habits, health status, overall fitness, and of course current physical activity.
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\nHowever, there can also be other significant sources of pollution beyond the human metabolic activity; essentially, we could say that we generate various odors and smells through our activities that are unpleasant and often harmful to health.
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Other significant sources of VOC include:
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cooking, frying, and other technological processes
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paints, adhesives
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cleaning and disinfecting agents
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furniture
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floor materials, carpets
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also scented candles, perfumes, and cosmetic products
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…
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\nIn the last century, scientists estimated that there are approximately 5 thousand volatile organic compounds. Today, with the increasing use of plastics, chemical agents, adhesives, paints, etc., their number is estimated to be more than 10 thousand different types.
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Why is air quality assessed mainly based on CO2 concentration?
\nThis is because the concentration of CO2 in exhaled air in indoor environments is about 50 times higher than in inhaled air. This is why the concentration of CO2 is a very good indicator of exhaled air.
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\nFor ventilation control, the fact is utilized that if the concentration of CO2 rises, the concentration of volatile organic compounds also rises. Therefore, when ventilation begins based on increased CO2 concentration, both CO2 and VOC concentrations decrease and we feel better. This is thanks to precise CO2 sensors that directly control the air handling units, allowing ventilation based on the current CO2 concentration.
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\nAnother reason is that, unlike the large number of different types of VOC substances, it is sufficient to monitor the concentration of only one substance – CO2 with reasonable costs and sufficient accuracy, which provides a very good indication of how exhaled the air in the given space currently is, thus giving us clear information about the need for ventilation. See the graph on the left:
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\nOf course, there are spaces where a CO2 sensor would show low values despite our unpleasant feelings, as it does not measure the odors and smells that occur there and represent the predominant air pollution in that space.
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\nExamples of such spaces may include:
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industrial, professional kitchens
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toilets
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changing rooms
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gyms, fitness centers
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…
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\nIn such spaces, the relationship between CO2 and VOC may be as shown in the graph on the right:
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The term “TVOC”
\nThis designation represents the so-called Total Volatile Organic Compounds (TVOC), which is a summary of VOC substances in the monitored air. TVOC generally encompasses a wide range of different organic substances that are often chemically very similar and difficult to distinguish, resulting in the emergence of several different TVOC standards.
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\nProtronix VOC sensors correspond with their sensitivity characteristics to two recognized international standards, namely the EPA (Environmental Protection Agency) and UBA (UmweltBundesAmt).
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The term “eCO2”
\nFurthermore, you may encounter the term eCO2 in relation to VOC measurement. To practically use VOC sensors similarly to CO2 sensors, some Protronix VOC sensors have what is known as eCO2 output (from the English estimated, or equivalent), which is an estimate (estimated = estimated) of the CO2 concentration made based on the currently detected VOC concentration. This estimate is based on the assumption that VOC produced by humans is proportional to exhaled CO2 (see Fig. 1). The advantage is that with the eCO2 output, it is then possible to work similarly to the signal from a standard CO2 sensor, which many installers are accustomed to, and the price of the VOC sensor is lower than that of a CO2 sensor operating on an optical principle.
