When cold and darkness descend on Germany, the air in the classrooms also becomes cloudy: In winter, the air quality is often questionable, according to the results of extensive measurements in 244 classrooms in the greater Munich and Mainz area. The investigation by Christian Schwarzbauer from the Munich University of Applied Sciences has not yet been scientifically examined.
The professor of medical technology and medical informatics recorded the CO₂ concentration in the classrooms to the minute throughout the 2021/22 school year. Exhaled carbon dioxide can not only cause headaches and concentration problems in large quantities, but also serves as a general indicator of air quality.
The measurements showed that the CO₂ guide value of 1000 ppm was exceeded most frequently in classrooms that were only ventilated through the windows. The measured values were too high on 24 percent of the teaching days. If the rooms had decentralized air conditioning systems that independently regulate the ventilation, the guide value was only exceeded eleven percent of the time. It was also comparatively effective a fan-based system developed at the Max Planck Institute for Chemistry in Mainz. It consists of fans that are built into the windows and hoods that suck in the air; According to the institute, around 1,000 classrooms are equipped with the system. With it, the CO₂ concentration was exceeded on 16 percent of the days. Naturally, mobile air filters could not reduce carbon dioxide pollution because the filters do not remove the gas from the air.
All systems had their pitfalls
The study cannot answer the extent to which the various systems prevent infections with Sars-CoV-2 or other airborne pathogens. Infections that actually occurred were not recorded, nor were virus particles measured. Rather, Schwarzbauer estimated the potential viral load based on the air quality.
Here, too, window ventilation in particular proved to be in need of improvement. Compared to the dose that is expected in an ideally ventilated room, the calculated possible virus concentration is significantly higher when the window is ventilated. The theoretical reference value was exceeded on 40 percent of all teaching days. In rooms with a fan-supported solution, the value was only exceeded on 16 percent of the days, in rooms with a decentralized air conditioning system on 13 percent of the days, and in rooms with mobile air filters on nine percent of the days. There are no epidemiological studies that could support such calculations by comparing real infections in different classrooms.
Overall, Schwarzbauer concludes, the decentralized ventilation systems and the fan system are a good compromise. In terms of both the CO₂ concentration and the assumed viral load, they reached relatively low values. At the same time, it was shown that all the methods examined can be error-prone. In individual cases, they were all unable to prevent very high CO₂ levels – in some cases the concentration was over 4000 ppm.
The winter was particularly problematic with window ventilation, probably because the cold prevented a frequent, long exchange of air. Schwarzbauer suggests CO₂ traffic lights and better education could help here. Mobile air filters and fan-based systems, on the other hand, were not always switched on. There were failures in air conditioning systems that probably went unnoticed for a long time. With all technical solutions, it is also important that they are correctly designed, adjusted and maintained for the respective room.
Schwarzbauer emphasizes that they measured the air during a peak phase of the corona pandemic: At that point, the focus on air quality was particularly great. Beyond such times of crisis, the air could very quickly become even thicker.