According to a recent announcement, researchers at the Goethe University in Frankfurt have found that air purifiers of the HEPA (H13) filter class can reduce the aerosol concentration in a classroom by 90 percent in half an hour. The study was published on the preprint server “medRxiv”, prior to publication in a scientific journal.
It has been known for some time that the novel coronavirus SARS-CoV-2 is not only spread via droplet infection, but that so-called aerosols may also play a role in the infection. A study has now shown that air filters in rooms can remove a large proportion of these particles – and do so in just 30 minutes.
The most dangerous route of infection of the coronavirus SARS-CoV-2 is through the air: when sneezing or coughing, infected persons throw relatively large droplets from themselves, which sink to the ground within a radius of two meters. Also important are the aerosol particles, much smaller liquid droplets that we also secrete when we speak or breathe. Studies have shown that infectious SARS-CoV-2 viruses can still be detected in such aerosols more than three hours after emission and this several meters away from patients.
Reduce aerosol concentration in a room
The liquid in such aerosol particles evaporates rapidly, making them smaller and allowing them to spread in a room within minutes. This also increases the risk of infection and makes additional safety measures necessary. Due to the accumulation and distribution of aerosols in the room, keeping the minimum distance to prevent infection may no longer be sufficient, writes the Robert Koch Institute (RKI). An effective air exchange can reduce the aerosol concentration in a room. Air filters also promise help in the fight against polluted room air.
Joachim Curtius, Professor of Experimental Atmospheric Research at the Goethe University in Frankfurt, and his research team spent a week testing four air purifiers in a school class with teachers and 27 students. The units had a simple pre-filter for coarse dust and lint as well as a HEPA and an activated carbon filter. According to the data, the air purifiers together converted between 760 and 1460 cubic meters of air per hour.
In addition to the aerosol load, the scientists determined the amount of fine dust and the CO2 concentration and examined the noise pollution caused by the devices. The result: half an hour after switching on, the air purifier had removed 90 percent of the aerosols from the air.
“On the basis of our measurement data, we made a model calculation that allowed us to make an estimate: An air purifier reduces the amount of aerosols so much that in a closed room the risk of infection by a highly infectious person, a superspreader, would also be very significantly reduced,” explains Prof. Curtius.
“However, an air filter does not replace the regular opening of the window, which again reduces the CO2 concentration in the room. Our measurements in the classrooms showed that the values were often above the recommended limits. Here we recommend the installation of CO2 sensors so that students and teachers can monitor this,” says Joachim Curtius. (ad)
“Therefore, we recommend that schools use HEPA air purifiers with a sufficiently high air flow rate this winter.” Noise measurements and a survey among the study participants showed that the noise of the air purifier was mostly not perceived as disturbing, unless the device was running at the highest level. In addition to the risk of infection, the air purifier also reduced allergen and fine dust pollution, as the researchers measured.
Reduce the risk of infection: Air purifier against aerosols
WashingtonNewsday Health and Wellness.