TVOC stands for Total Volatile Organic Compounds, i.e. the total amount of volatile organic compounds in indoor air. Because there are a great many VOCs and measuring them individually is often difficult, TVOC measurement gives an overall picture of the chemical quality of indoor air. It helps to detect, for example, emission peaks or shortcomings in ventilation.
How is TVOC measured?
1. Collected samples (laboratory method)
An air sample is collected, for example with an adsorbent cartridge, and analysed in a laboratory using gas chromatography–mass spectrometry (GC-MS). This gives precise concentrations of individual VOCs, from which the TVOC value is calculated.
2. Continuous measurement with a sensor connected to an online service
Many devices use real-time sensors, such as those based on MOx, PID or FID technology. They measure the total concentration of VOCs but do not distinguish between individual compounds. The result is given as a TVOC index or as a concentration value.
Strengths and limitations of the methods
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The laboratory method provides a precise analysis and makes it possible to identify individual compounds. However, it is slow and based on a single sampling moment, when concentrations may happen to be either high or low, so the result does not necessarily reflect the actual variation. Costs are added by the sampling work and travel, shipping the samples to the laboratory, and the laboratory analysis and report.
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A sensor provides real-time information on how TVOC levels vary – for example, on how well the ventilation in a space is working – but it cannot replace official analyses, because individual compounds are not identified and results may vary from one device to another.
TVOC concentrations, variation and guideline values
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TVOC concentrations are affected by many factors, such as new materials (paint, furniture, adhesives), cleaning, temperature and ventilation. In new premises, concentrations can remain elevated for several months unless ventilation is sufficient.
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In Finland, the official action limits (the Housing Health Decree issued by the Ministry of Social Affairs and Health) apply only to samples collected with the laboratory method: TVOC 400 µg/m³ and 50 µg/m³ for an individual compound (calculated as toluene equivalents). There are no official limits for results from continuous sensors, but as practical reference values, levels below 300 µg/m³ are generally considered safe, while concentrations above 500 µg/m³ that persist for long periods call for further investigation.
What do TVOC values tell us in practice?
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A real-time sensor helps to detect temporary emissions (e.g. cleaning, new materials) and recurring deterioration in air quality.
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The laboratory method gives a precise picture of which compounds are present and in what concentrations – important information when planning corrective measures.
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Combining both methods provides comprehensive information: the sensor reveals the problem, and the laboratory tells you what caused it.
VOCs are a useful parameter to monitor in all kinds of buildings. In addition to sensory observations and user experiences, it is worth keeping track of them by measuring.