One of the simplest ways to protect against corona is to get out into the fresh air. There – to put it simply – the wind whirls the viruses away, making infection less likely.
But this also means: at the latest in autumn, when we are indoors more and windows remain closed, the risk of infection increases.
The majority of the research community is convinced that droplets and the even smaller aerosol particles play a crucial role in the transmission of sars-cov-2. Aerosol particles can hover in the air for hours to days. The former president of the international society for aerosols in medicine, gerhard scheuch, referring to asymptomatic infected people who have been proven to have transmitted the virus, says: "i believe that simply breathing is enough."
And this is basically where the problem lies: in a closed room, a sick person breathes, coughs, sneezes again and again in batches of viral clouds. If there is no wind, the viruses spread around the room and the corona concentration increases. Therefore, the robert koch institute warns that prolonged stays in small, poorly ventilated or unventilated rooms can increase the likelihood of transmission through aerosols, even over a distance greater than two meters.
How much higher is the danger in interior rooms than in rooms under a roof?? There are no concrete answers to this question. Scheuch refers to a study from china, according to which of the 318 outbreaks investigated with three or more infection traps, only one took place in the open air.
But not all indoor spaces are the same, as scheuch explains: "in gyms, of course, the physical exertion can significantly increase the production of aerosols through breathing."In a classroom with many screaming children running around in confusion, the danger is also greater than in an office with a few adults (seated in an orderly manner). In the inn, on the other hand, loud talking, humming, and singing could strengthen the spread.
The solution here is also: wind. And the air should ideally be as fresh as possible. The head of the hermannrietschel institute, the institute for energy technology at the technical university of berlin, martin kriegel, and his team have investigated how the particles are distributed in the room. He comes to the conclusion: "in principle, it can be stated that at typical air exchange rates in residential and office buildings, the pathogens remain in the room for hours. Sinking speed and also air renewal take a very long time. Any increase in the supply of room air is therefore generally sensible."
Dieter scholz of the department of vehicle technology and aircraft construction at the university of applied sciences in hamburg argues similarly. Cross ventilation with open windows on opposite sides of an apartment, for example, is said to be the best solution. Even tilted windows brought more than a built-in ventilation system, says scholz. The problem with this, especially with regard to the autumn: just as quickly as possible viruses are blown out, the warm air also disappears.
The cold seasons of autumn, winter and probably also spring will bring one more major problem this year. What to do?
A team from the institute of fluid mechanics and aerodynamics at the university of the german armed forces in munich has investigated a room air purifier whose filter combination can remove 99.995 percent of even very small aerosol particles from the air in a room. In an 80-square-meter room, the aerosol concentration can be halved in six minutes. Because the aerosols are filtered out, the machines do not become a source of viruses, says the team around christian J. Kahler firmly. They recommend air purifiers for schools, offices, shops, waiting rooms, clubhouses, lounges and dining rooms.
Aerosol expert scheuch also considers CO2 measuring devices for closed rooms to be helpful. "The CO2 content is a mab for 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 cleaners at the same time, they do not help anymore. "Because then the CO2 content in the room goes up, but the air remains pretty much free of virus aerosols."Here then an additional particle measuring device could help, which determines the aerosol concentration.