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When students at the Werner von Siemens Schule in Mannheim, Germany return to school next week, they will be the first to have a detector in their classroom that measures the amount of aerosols in the air.

The Proxi Cube, as the device is called, was developed by the Mannheim University of Applied Sciences. Among other things, the box features an optical sensor that counts every particle between 300 nanometers and 10 micrometers. These can be either dust particles or tiny liquid droplets.

The device calculates the amount of water droplets in the air based on the difference between two measurements.

The meter is capable of making a distinction between the two. A relatively simple but well thought-out principle was used to achieve this. For the aerosol detector, the researchers used the same sensor technology as is used for measuring particulate matter, but then in a dual package. “One sensor measures the air drawn into the room, while the second one heats that air so that the liquids evaporate. The device then calculates the amount of water droplets present in the air based on the difference between the two measurements,” says Thomas Schäfer of the Center for Mass Spectrometry and Optical Spectroscopy, part of the Mannheim University of Applied Sciences.

Aerosol meter© Nevoox Europe

This ensures that a distinction can be reliably made between solid and liquid particles. Measurement data is displayed as graphs. This means that the concentration of aerosols can also be followed over a longer period of time. The Proxi Cube issues a warning as soon as too many aerosols accumulate in a room.

Critical aerosol concentration

Airborne aerosols that are inhaled are considered a major risk factor for contracting the coronavirus. Especially in moderately ventilated indoor spaces, there is a real danger that the tiny droplets from breathable air will accumulate in the air for a longer period of time and spread the virus. This is the reason why many public spaces, such as schools, are rigorously ventilated. The question is whether this is done thoroughly enough, or even too much. An aerosol meter can be useful because it signals when the aerosol concentration reaches a critical level. Windows and doors can then be opened and closed with a greater sense of safety.

The Proxi Cube is manufactured by the German company Nevoox Europe, which was founded just seven months ago in Mannheim. The start-up focuses on innovative solutions in the disinfection field. The Proxi Cube will also be available in stores from April onwards.

Distance learning

Pupils of the Werner von Siemens Schule will have to be patient a little while longer. No classes will be held at the school until at least the middle of next week due to the corona crisis. Distance learning will take place instead.

Read about a German-made air filter system that removes aerosols from the air in school classrooms here.