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Critical CO2 concentrations

Published 2023-10-05

Critical CO2 concentrations

CO2 and aerosols

Scientific studies show that there is a relationship between CO₂ levels and aerosol concentrations in the air. Aerosols are mainly produced when we breathe and speak and can transmit pathogens and viruses such as coronavirus. Testo’s measurement technology can help you detect elevated CO₂ levels at an early stage. With optimally adjusted ventilation systems, it is possible to prevent airborne transmission of pathogens. This in turn can reduce the risk of diseases such as COVID-19. As an example, the German government recommends controlling CO₂ levels in the air to reduce the risk of infection.

What are aerosols?

Illustration of inhalation of aerosols

Aerosols are small, tiny droplets that are released into the air when exhaled. They are only a few micrometers or nanometers in size, which means they float in the air and sink very slowly to the ground. In other words, they are spread when you breathe, speak or sing. Each person permanently emits CO2 and aerosols. As a result, pathogens and viruses, such as e.g. coronavirus, are transmitted from one person to another.

Aerosols in premises

Logger on wall, monitoring CO2

In general, the risk of infection is significantly higher indoors than outdoors because aerosol particles remain in the air longer. Therefore, due to the higher aerosol concentration, there is a risk of undetected spread of pathogens. If the aerosol concentration is high enough, we can breathe in aerosols even if we keep our distance from each other. This is called airborne transmission by aerosols. The lower the aerosol concentration, the lower the dose of aerosols a person can inhale and thus the lower the risk of infection. This risk can be reduced by good air exchange or by mixing the air with fresh air. This requires good ventilation or optimal adjustment of the ventilation system.

Measuring CO₂ to counteract aerosols

CO2 measurement with a portable meter

CO₂ levels increase when many people are in a poorly ventilated room. By measuring the CO₂ concentration, it is possible to calculate the likely aerosol load. The higher the CO₂ level, the higher the risk of inhaling aerosols that another person has exhaled shortly before. The CO₂ concentration is therefore a type of indirect measurement for possible exposure to aerosols. The quality of indoor air in offices and homes is usually assessed by the CO₂ content. A CO₂ meter can therefore help to see how polluted the air in a room is. An indoor CO₂ concentration of up to 1000 ppm (parts per million) is acceptable. In comparison, outdoor air has a CO₂ value of about 400 ppm.

Humidity counteracts viruses in aerosols

Moisture measurement with a portable meter

Very low temperatures and low humidity promote the survival time of viruses in the air. Even at average temperatures of 20-30°C and low humidity, viruses have a long survival time. However, in a range between 40 %RH and 60 %RH, the aerosols shrink so much that the salt concentration in the aerosol core increases, killing bacteria and microorganisms. Therefore, in addition to measuring CO₂, regular measurement of relative humidity is also recommended.

Nordtec Inomhusklimat

CO2 / aerosols

Application: Measurement of CO2 and aerosols in indoor air

Measurement solution: testo 160 IAQ, testo Saveris 2

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Contact persons

Mattias Töreskog


Mattias Töreskog

Area of responsibility: Technical support, Food, Life Science
031-704 10 84
031-704 10 70