Corona trap interior

Christine Albert studied German linguistics and literature as well as Scandinavian studies at the Albert Ludwigs University in Freiburg. She is currently doing a traineeship at Hubert Burda Media and is writing, among other things, for

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One of the simplest means of protection against corona: Get some fresh air. There - to put it simply - the wind whirls the viruses away, which makes infection less likely. But that also means: by autumn at the latest, when we are more indoors again and the windows remain closed, the risk of infection increases.

Droplets play a crucial role

The majority of the research community is convinced that droplets and the even smaller aerosol particles play a decisive role in the transmission of Sars-CoV-2. Aerosol particles can float in the air for hours to days. The former president of the International Society for Aerosols in Medicine, Gerhard Scheuch, says with a view to symptomless infected people who have been shown to have transmitted the virus: "I think that just breathing is enough."

And this is exactly where the problem lies: In a closed room, a sick person breathes, coughs and sneezes again and again in bursts of virus clouds. If there is no wind, the viruses spread throughout the room and the corona concentration increases. The Robert Koch Institute therefore warns: If you stay in small, poorly or non-ventilated rooms for a long time, the probability of transmission by aerosols can increase even over a distance greater than two meters.

Indoor hazard

How much higher is the danger indoors than outdoors? There is no concrete answer to that. Scheuch refers to a study from China, according to which of the 318 outbreaks investigated with three or more cases of infection, only one took place in the fresh air.

But not all interiors are the same, as Scheuch explains: "In fitness studios, of course, physical exertion can significantly increase the production of aerosols through breathing." In a classroom with many screaming, messed up children, the danger is also greater than in an office with a few (well-behaved) adults. In the tavern, on the other hand, loud speaking, noise and singing could increase the spread.

1st solution: Fresh air through the wind

Here, too, the solution is: wind. And the air should ideally be as fresh as possible. The head of the Hermann Rietschel Institute, the Institute for Energy Technology at the TU Berlin, Martin Kriegel, and his team investigated how the particles are distributed in space. He comes to the conclusion: "In principle, one can state that with typical air exchange rates in residential and office buildings, the pathogens remain in the room for hours. The rate of descent and the air renewal take a very long time. Any increase in the outside air supply is therefore generally sensible."

Dieter Scholz from the Department of Vehicle Technology and Aircraft Construction at the Hamburg University of Applied Sciences argues similarly. Cross ventilation with open windows on opposite sides of an apartment, for example, is best. Tilted windows also bring more than a built-in ventilation system, says Scholz.The problem with this, especially with a view to autumn: The heat disappears just as quickly as possible viruses are blown out.

The cold seasons of autumn, winter and probably also spring bring one more problem with them this year. What to do?

2nd solution: clean room air

A team from the Institute for Fluid Mechanics and Aerodynamics at the University of the Federal Armed Forces in Munich has examined a room air purifier with a filter combination of which 99.995 percent of even very small aerosol particles are separated from the room air. In an 80 square meter room, the aerosol concentration can be halved in six minutes. Because the aerosols are filtered out, the devices would not turn into viruses either, says the team around Christian J. Kähler. They recommend room air purifiers for schools, offices, shops, waiting rooms, club houses, lounges and dining rooms.

Aerosol expert Scheuch also considers CO2 measuring devices to be helpful in closed rooms. "The CO2 content is a measure of the air quality in a room with several people. Then they would help as a warning system," he explains. But if you use room air purifiers at the same time, they no longer help. "Because then the CO2 content in the room goes up, but the air still remains fairly virus-aerosol-free." An additional particle measuring device, which determines the aerosol concentration, could help here. (approx / dpa)

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