Mannheim University of Applied Sciences develops aerosol detector - device helps schools comply with their ventilation concepts

The competence center CeMOS (Center for Mass Spectrometry and Optical Spectroscopy) at Mannheim University of Applied Sciences is developing a handy system for measuring aerosols indoors. In doing so, it is using a sensor that was originally intended for the determination of fine dust concentrations and was developed within the framework of the M2Aind UAS impulse funding program. The M2Aind cooperation partner, the company ProxiVision GmbH in Bensheim, is now producing the first prototypes under the working title ProxiCube and is also already in negotiations with the corresponding sales partners. Schools in Mannheim have expressed great interest, and the City of Mannheim's Economic Development Department is promoting the development and application as part of the Smart Production/Industry 4.0 innovation network; if all goes well, the first classrooms could be equipped with ProxiCubes as early as the beginning of 2021. The Werner von Siemens School on the Neckarpromenade is the first school to have already ordered five cubes from Proxyvision.

Aerosols from the air we breathe are considered the greatest risk factor for infection with the SARS-CoV2 coronavirus. Particularly in poorly ventilated indoor spaces, there is a risk, especially in winter, that the tiny droplets from the air we breathe will collect and spread the virus - which is why strict ventilation policies are now in place in many public places, and especially in schools. But a residual uncertainty always remains: Has the room really been ventilated thoroughly enough? At what point does the aerosol concentration become critical, and can one not dare to keep the window closed for a while after all?

CeMOS researcher Dr. Thomas Schäfer asked himself these questions and converted a battery-operated, portable device for measuring fine dust, which he helped to develop a few years ago, into an aerosol detector. He explains why this is so easy: "The optical sensor makes no distinction between dust particles and tiny liquid droplets. It counts every particle between 300 nanometers and 10 micrometers in size that passes the light barrier inside it."

For the aerosol detector, Schäfer and his team thus use the same sensor technology as for measuring fine dust, but in a double pack: one sensor simply measures the room air that is sucked in, while the second heats the sucked-in air to such an extent that liquids evaporate. The device then uses the difference between the two measurements to calculate the amount of aqueous droplets present in the air - enabling it to reliably distinguish between solids and liquid particles.  The measured data is output to users so that aerosol concentrations can be monitored and documented over longer periods of time; the development team is also planning a dashboard on which multiple rooms can be monitored via a traffic-light system and which issues a warning as soon as too many aerosols collect in a room. ProxiCube has since been filed for a patent.