Using CO2 and humidity sensors against the pandemic:
Who is building a reliable CO2 traffic light for offices and rooms?


Scientists have proven that COVID-19 is primarily spread by aerosols in exhaled air. Aerosols do not pose such a threat outdoors with the recommended minimum distance. However, the situation is totally different in enclosed spaces. Viruses will often remain in the air for several hours indoors.

Supply fresh air or ventilate! You are no doubt familiar with this recommendation or instruction from your working and family life.

But what has COVID-19 got to do with the CO2 concentration and humidity in rooms?

The amount of suspended aerosols can be inferred from the CO2 concentration in the air. Hence, the quality of the indoor air, including its CO2 content and its relative humidity, is another indicator for a possible coronavirus infection risk. CO2 values of less than 1,000 ppm and a relative humidity of 40% to 60% are desirable.



A system for continuous monitoring and control of the indoor air quality should be easy to read, flexible and reliable. For example, measurement of the air quality via a CO2 traffic light: Green light = "Everything OK" or red = "Ventilate immediately".

Who needs something like this, preferably immediately?
A simple calculation: we have around 40,000 schools with an estimated 20 rooms per school in Germany.
This means that 800,000 air quality traffic lights are required for the school sector alone.

Who builds it?
A sensor module that can be easily integrated and has everything important on board is essential for the construction of an air quality traffic light. You will find this in the SCD30 from SENSIRION. This sensor module has already been tried and tested a million times over in the field of air quality measurement in heating, ventilation and air conditioning (HVAC).
In addition to the precise CO2 sensor, a top-class humidity and temperature sensor has been integrated in the module. GLYN can supply you with the appropriate starter kit: Unpack, connect and start your development
right away.

Read the most important facts about "Using CO2 and humidity sensors against the pandemic" and the appropriate sensor products here:

Coronavirus is spread by aerosols
Aerosols play an important role in the spread of the coronavirus.
Researchers at the University of Florida have shown that the viral load of aerosols can be high and infectious.

The tiny droplets are secreted by humans through the mouth and nose when breathing, and even more so when speaking, shouting or singing.

These aerosols do not pose such a threat if you keep the recommended minimum distance outside. They are dispersed by the wind, while UV radiation from the sun inactivates the virus.

However, the situation is totally different in enclosed spaces. The aerosols we exhale are suspended in the air for a long time, due to their minute size. Depending on the size of the particles, they can remain in the air for minutes to hours at a time.
The disease can be transmitted if a healthy person inhales droplets contaminated with the coronavirus.

The conclusion is that the aerosol load in enclosed spaces must be kept as low as possible to reduce the potential risk of infection.

This can be achieved with an increased supply of fresh air in buildings equipped with modern ventilation or air conditioning systems.
Some of these systems even have HEPA (High Efficiency Particulate Air) filters, which are able to retain some of the aerosols.

However, this technology is not available in most offices, classrooms, nursery schools, restaurants and stores. Sufficient fresh air can only enter these rooms by opening the windows.
And this is usually not possible in schools and nursery schools for safety reasons. The larger windows are tightly closed so that children cannot fall out. Ventilation can then only be provided e.g. through small fanlights.

In the warmer months of the year, windows might be left open permanently to allow air exchange. This is no longer possible when the colder autumn days begin, because the inside temperature will be too cold for working and learning, and because we would literally be throwing heat out of the window.

At this point, a changeover to needs-based ventilation is required. The question is, how can you determine this need?
Measuring devices that are capable of measuring aerosols in the air are already available today. However, they are complicated and expensive. A different, simpler and relatively inexpensive approach therefore has to be found.

CO2 measuring devices or, even simpler, CO2 traffic lights are the solution.
The CO2 traffic lights have displays in green, yellow and red and warn of excessive amounts of CO2 in the air.
A possibly increased risk of infection can be inferred from this.

What does the CO2 concentration in rooms have to do with the risk of coronavirus infection?
The idea behind this is as simple as it is elegant.

Every human exhales about eight litres of air per minute. This air has previously had intensive contact with our lung tissue and contains CO2 in addition to the aerosols described above. This CO2 accumulates in the air in the room and can be measured very easily with the sensors available today, and therefore used to categorise the current potential risk.

At what CO2 concentration should ventilation be started?
A CO2 concentration of approx. 1,200 ppm (parts per million) means that almost 2% of the air in the room has had lung contact at least once.
In other words, every 50th breath that a person takes in this room consists of air that has already been exhaled. The risk level of coronavirus infection from this air is yet to be researched. Nevertheless, this value is a good indicator.

The CO2 content of the air in rooms was a parameter for indoor air quality even before coronavirus times.
The recommendation of the Federal Environment Agency is that ventilation should be provided above a value
of 1,000 ppm, in order to maintain productivity and the ability to concentrate.

By way of comparison: fresh air contains about 400 ppm of CO2. The proportion is approx. 100 times as high in exhaled air, i.e. 40,000 ppm.

How air humidity affects aerosols
The University of Missouri in Columbia has published a research paper showing that humidity has a decisive influence on the lifetime of aerosols.
According to the researchers' calculations, particles of medium size can remain in humid air up to 23 times longer than they would in dry air. Furthermore, the moisture content of the air also determines how far away the small particles can move from their source.
If the air is very dry, the droplets evaporate faster and therefore cannot last or move in the air for long.
To make the most of this effect, the relative humidity should therefore be as low as possible.
However, a relative humidity below 40% causes dehydration of the mucous membranes – an important protective mechanism against infections in humans.

There were also recommendations for relative humidity, even before the coronavirus. Depending on the temperature, this should be between 40% and 60% RH.

Based on our current knowledge, monitoring and controlling the CO2 content and relative humidity of the room air is an indicator of a possible risk of coronavirus infection. CO2 values of less than 1,000 ppm and a relative humidity of 40% to 60% are desirable.

Reliable measurement of CO2 and relative humidity
The SCD30 from SENSIRION is a sensor module for air quality determination and for applications in the field of heating, ventilation and air conditioning (HVAC).

The module contains a CO2 sensor together with a top-class humidity and temperature sensor.

The CO2 sensor works on the NDIR (Non Dispersive Infra-Red) principle and makes use of the fact that CO2 molecules absorb infrared radiation in the range of 4.3 µm. Other gas molecules absorb hardly any light in this wavelength.

Inside the sensor there is a light source that emits infrared light. Opposite the light source there is a sensor that measures the radiation intensity in the 4.3 µm range. A decrease in this radiation intensity is a reliable sign of the presence of CO2.

The two-channel principle means that the sensor is designed to automatically compensate for long-term drifts and is very user-friendly with a lifespan of approx. 15 years.

Its compact size of just 35 mm x 23 mm x 7 mm enables easy integration in various applications.
The SCD30 is fully calibrated and linearised.

The SCD30 is available ex stock from GLYN.
Further information can be found here:

CO2 sensor Artikel Datasheet Webshop Measurement range
01_CO2Sensor_250px SCD30 Datasheet Webshop CO2: 0 – 40,000 ppm
RH: 0…100 % ±3,0 %
T: -40…70 °C ± 0,4 °C

Quick start with evaluation kit
A modular evaluation kit is available so you can start measuring CO2, humidity and temperature immediately.

Every kit combines plug-and-play hardware with a user-friendly viewer software (for Windows, Linux or macOS), the ControlCenter and the requisite cables.

The evaluation kit can be individually configured in just three simple steps


  • Order the SEK SensorBridge…
  • …select the required sensors…
  • …load the SEK ControlCenter viewer software…

…start the evaluation!


SensorBridge Article Datasheet Webshop
data/glyn/media/img_big/10_Sensirion_SEK-SensorBridge2_250px.jpg SEK-SensorBridge Datasheet Webshop


CO2 sensor with cable Article Datasheet Webshop Measurement range
10_Sensirion_SEK-SCD30-Sensor_250px SEK-SCD30 sensor Datasheet Webshop

CO2: 0 – 40,000 ppm
RH: 0…100 % ±3,0 %
T: -40…70 °C ± 0,4 °C


Viewer software Article Download
10_ControlCenter_250px ControlCenter viewer software Software

Outlook –
SCD40 with photoacoustic measuring technology


The SENSIRION sensor family will be expanded with a miniaturised CO2 sensor, based on Sensirion's unique PASens® technology. This is planned for the last quarter of 2020/first quarter of 2021. 

The sensitivity of the CO2 sensors commonly used today, which are based on the NDIR principle, is directly proportional to the optical beam path. Significant shrinkage in the size of the sensor element therefore leads to impairment of the sensor performance. 

The PASens® technology is based on a photoacoustic sensor principle. This allows extreme miniaturisation of the CO2 sensor without compromising the sensor performance. This is due to the fact that the sensor sensitivity is independent of the size of the optical cavity. This measuring method has enabled a reduction in the housing dimensions to 10.1 mm x 10.1 mm x 6.5 mm.

The photoacoustic effect was discovered as early as 1880 but was not practicable for sensors, due to the lack of technological components. However, laboratory-scale photoacoustic instruments are well established, owing to their excellent performance.

Like the SCD30, the SCD40 includes an additional humidity and temperature sensor.

Start the development of your air quality traffic light now.
Further information as well as all components and starter kits are available on request/order.

Analog Power & Sensors

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