Aerosols from the air we breathe are considered the greatest risk factor for infection with the SARS-CoV-2 coronavirus. In badly ventilated rooms, there is a risk that the tiny droplets from the breathing air will accumulate and thus spread the virus – which is why strict ventilation concepts are now in place in many public spaces and especially in schools. But some uncertainty always remains: Has the room been ventilated thoroughly enough? At what point does the aerosol concentration become critical, and can we dare to keep the window closed for a while longer?

The Hochschule Mannheim has developed a solution to this problem: At CeMOS (Center for Mass Spectrometry and Optical Spectroscopy), scientists had already developed a battery-powered, portable device for measuring fine dust a few years ago, which has now been converted into an aerosol detector. CeMOS researcher Dr. Thomas Schäfer was substantially involved in both developments and explains why the transformation was so easy: “The optical sensor makes no difference 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 therefore use the same sensor technology as for the fine dust measurement, but in a twin pack: The device draws in room air and directs it past two sensors. One of them simply measures the air, the other one heats the air up until liquids evaporate. From the difference between the two measurements, the device calculates the number of aqueous droplets present in the air – this enables it to reliably distinguish between solids and liquid particles. The measurement data can be, for example, output as graphs, so that the aerosol concentration can be monitored and documented over longer periods of time. In addition, a dashboard is used on which several rooms can be monitored via a traffic light system and which issues a warning as soon as too many aerosols accumulate in a room. Later, there will also be an app for mobile devices.

In the meantime, the marketing of the device has started: ProxiVision GmbH, cooperation partner of the Hochschule Mannheim, has produced the first devices, called Proxi Cube. Through active involvement in the Smart Production network, an initiative of the Economic Development Department of the City of Mannheim, the Werner-von-Siemens School was won over as one of the first users. Moreover, Nevoox Europe GmbH, a Mannheim-based sales partner was found who has taken over exclusive worldwide sales of the device.

On February 16 2021, Nevoox Europe GmbH, together with the City of Mannheim and the Smart Production network, officially handed over the first Proxi Cubes to the Werner-von-Siemens School: When the pupils of that school return from the carnival holidays, their classrooms will be the first in Germany to be equipped with the Proxi Cubes. Other schools in the Mannheim area are to follow.

From April, the Proxi Cube will also be available in stores, as the technology is not only interesting for schools: “Hotels, bus companies, restaurants, hospitals and many other industries can also use this technology for the safety and well-being of employees and guests,” says Thomas Walch, managing director of Nevoox Europe GmbH. “Until now, a large number of sensors were needed to determine so much data from the air in the room. The fist-sized Proxi Cube does all this independently and automatically.”