CO2 monitor reduces the threat of the COVID-19


More evidence that CO2 levels in buildings are closely related to airborne infections. As such, CO2 monitor could act as “canaries in the coal mine” to mitigate the threat of the COVID-19.

 The air exhaled by people who stay indoors produces CO2. Everyone in the building will exhale about 8 liters of air per minute: air that is already in close contact with lung tissue. In addition to CO2 at a concentration of about 40,000 ppm, exhaled breath contains tiny droplets (aerosols) that, because of their size and can float in the air for long time. These droplets will contain any viral particles present in the lungs. Research has shown that infection mitigation can be implemented with CO2 monitor in the field.

It is generally accepted that the sinking velocity of such aerosols is typically a few meters per hour, and that the decline in the infectious activity of biological viruses has a half-life of about three hours under laboratory conditions. it means that the indoor air is polluted for long time. The disease can spread if healthy people inhale these contaminated droplets and if they contain more viral particles than the minimum infectious dose. While it is difficult to directly measure virus levels, energy-harvesting wireless sensors are one of the ideal ways to monitor co2 levels and thus prevent air pollution.

Indirect measurement of COVID-19 transmission

LMore evidence that airborne transmission is a major factor in virus transmission, so it can be inferred that CO2 levels in rooms and other enclosed spaces can act as a proxy for COVID-19 transmission risk.

Professor Shelley Miller, a leading aerosol scientist, said: “Because the covid-19 is airborne, higher co2 levels indoors may mean a higher chance of transmission if an infected person is indoors.” In other words, the more fresh air in a building, the better. Fresh air will dilute any contaminants in the building, whether viruses or otherwise, and reduce the risk of infection for anyone indoors. “

 A 2019 study on TB outbreaks by Taipei University in Taiwan provided detailed evidence. Many rooms have poor ventilation with co2 levels exceeding 3000 ppm. The outbreak stopped when engineers dropped the concentration below 600 ppm.

What the CO2 level is safe?

Elsewhere, Professor John Wenger, director of the UCC Centre for Atmospheric Chemistry Research, suggested that if CO2 is used as a surrogate for COVID-19 in classrooms, the target should be 1000 ppm, noting that room-level transmission is ” The point. It’s in the air and it can fill an entire room. The number of viruses in the air will build up and our exposure will increase. If you’re indoors, in a poorly ventilated room for a long time, even from a distance, you may risk There is a big risk because the air moves around.”


Indoor CO2 monitor using an easy-to-install and low-cost sensor promises to enable large-scale monitoring of indoor aerosol transmission risk for Covid-19 and other respiratory diseases.

Different CO2 level targets should be set based on the environment and type of activity, as infection risk levels have been shown to vary by a factor of 100 or more depending on the situation and type of activity. Factors such as the number of people infected in an area and measures such as wearing masks or air filtration may reduce the presence of airborne viruses without lowering CO2 levels. Certain activities, such as talking, singing and shouting, increased viral emissions far beyond CO2 levels. Both CO2 and viruses are diluted by outdoor air ventilation. However, they cannot be removed by air recirculation, eg through a heat exchanger.

Breathing fresh air

If we are in a room with several people, the monitor of CO2 concentration can measure what percentage of the air we breathe in has been exhaled by other people. The mass balance showed that the measured CO2 concentration of about 1200 ppm means that almost 2% of the air in the room has already touched the lungs at least once. At this level, every 50 breaths a person takes into the room consists of air that has already been exhaled. Quantifying specific infection risk is more complicated because specific infection risk depends on a variety of factors that are still being studied in depth. Despite these caveats, it is clear that CO2 measurements offer a cost-effective solution to classify current risks from potentially infectious aerosols.

Strategies to reduce the risk of infection

Putting this research into practice, Germany’s Federal Environment Agency has drawn up general guidelines for the health assessment of carbon dioxide in indoor air, including recommendations for SARS-CoV-2 – also relevant to COVID-19. Therefore, concentrations of <1000 ppm are hygienically harmless. The guidelines classify concentrations between 1,000 and 2,000 ppm as suspicious, and anything above 1,000 ppm as unacceptable. CO2 is also an important indicator of DGHK (German Association for Gifted Children) regarding school prevention.


Likewise, the UBA (Umweltbundesamt – German Environment Agency) working group on ventilation recommends the use of CO2 signal lamps for this purpose. The DGVU (Unfallkasse) went further, advocating a target of 700 ppm in classrooms during the pandemic. The latest findings are outlined in the UBA guide ‘School ventilation’ (15.10.20), created for the KMK (Kultusminister der Länder of the German Bundestag).


Ventilation means not only air exchange, but also heat loss in winter. Sustainable strategies should also take this impact into account. In places where modern air conditioning technology with heat exchangers is not available, it is helpful to only monitor CO2 and demand-driven or regular manual cross ventilation. REHVA, the European Federation of Heating, Ventilating and Air-Conditioning Associations, has called for the installation of carbon dioxide monitors with traffic lights in school classrooms, “at least in schools where ventilation depends on open windows and/or grills”

Implementation of CO2 sensor

To follow these strategies, CO2 monitor equipment must be reliable and easily placed where it is needed. Ideally, they would need to be connected, for example, to trigger an alarm when the CO2 concentration crosses a threshold, or even send an alarm to a building management network or to a smartphone over a wireless network. Wireless, battery-free sensors represent the ideal solution. Easy to install and easy to maintain, the sensor utilizes energy harvesting technology to absorb energy from the surrounding environment such as motion, light or temperature differences. This solution can be rapidly deployed without the need for special installation or wiring, allowing continuous monitoring of co2 levels in the surrounding air.


By sending measured values ​​to receivers or gateways for further processing, alarms can be triggered and appropriate actions initiated. For example, indoor ventilation systems can be activated to reduce CO2 concentrations. Also, these CO2 sensors have a wide range to work within standard ecosystems such as the EnOcean Alliance. This means they can easily be combined with other devices that are integral to COVID-19 measures, such as room occupancy sensors and access control.

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