Indoor Air Quality Monitoring


We feel comfortable and safe at home. It doesn't immediately occur to everyone that the air we breathe indoors could be contaminated with pollutants and therefore harmful to our health.

Pollutants in indoor air have many causes: Gases released from furniture or building material, mold spores, fungi and viruses. While they are very different, they all have one thing in common: they impair our well-being. Since the 1970s, more attention has been paid to the effects of spending time inside. The occuring symptoms are summarized in the umbrella term "sick building syndrome". In addition to pollutants in the air, the syndrome is also triggered by poor lighting conditions, noise pollution and psychological stress.

Outgassing from Everyday Objects

Indoor air pollution is considered a high risk for premature deaths. The main contributors to poor air quality are volatile organic compounds (VOCs). These are substances that are volatile under ambient conditions and therefore potentially harmful.


VOCs such as benzene, formaldehyde and naphthalene are emitted from everyday consumer products or building materials and have been shown to have harmful health effects. In addition, VOCs are known to react with ground-level ozone to form secondary pollutants that can affect human health. Environmental authorities around the world have now set guideline values to limit the concentration of such VOCs in public indoor spaces. To comply with these guideline values, reliable and continuous measurements are important. Since most VOCs show good absorption in the infrared spectrum, techniques such as non-dispersive infrared spectroscopy (NDIR) are particularly well suited.

CO₂ as an Indicator for Air Quality

Carbon dioxide (CO₂) has been a reliable indicator of air quality for a long time. CO₂ is a natural component of our atmosphere. In dry outdoor air the level is about 400 ppm.


In closed rooms, however, this value can quickly increase, especially if several people are in the room. With each breath, humans emit about 40,000 ppm of CO₂, steadily worsening the air quality. As the CO₂ concentration increases, other pollutants also accumulate in the air. Thus the CO₂ value in the air can be considered as an overall factor for the pollution load. Up to a CO₂ concentration of 1000 ppm, the air is classified as hygienically clean; at higher values, the air needs to be replaced or purified. For the measurement of typical CO₂ concentrations in the air, the NDIR technique is excellent because CO₂ has good absorption at 4.26 µm in the mid-infrared.

Energy-efficient Control of Heating and Ventilation Systems

Gas sensors with various technologies have long been used in heating, ventilation and air conditioning (HVAC) systems to enhance their control. One of the biggest challenges in developing effective HVAC system control is optimizing it for actual occupancy of the building.

Demand Controlled Ventilation (DCV) has become a significant element in achieving this goal. CO₂ gas sensors are often used to measure usage in enclosed spaces (homes, office buildings, vehicle cabins, etc.). With their help, HVAC systems can respond to the situation as needed and adjust performance. Especially in terms of energy efficiency, intelligent control is very valuable. It can prevent unnecessary ventilation and thus prevent cold from escaping rooms in summer or heat from escaping rooms in winter. CO₂ gas sensors based on the principle of optical spectroscopy offer decisive advantages for this application, such as sensor stability and low operating costs with a long service life.