B.When reading the planned changes in the Infection Protection Act, many aerosol experts are likely to have been annoyed. According to the draft published last Tuesday, the federal government wants to close zoos with an incidence of 100 reported corona infections per 100,000 inhabitants, largely ban meetings in public spaces and introduce a curfew after 9 p.m. – all of this restricts life in the open air. Five aerosol researchers had previously turned to the government with a lot of media hype: In an open letter, they criticized that the public debate did not reflect the state of scientific knowledge, namely that the risk of becoming infected with Sars-CoV-2 lurked inside.
If meetings in parks were forbidden and waterfront promenades were closed, it would appear as if it were particularly dangerous outside. The authors blame curfews as “misleading communication”. Instead, it should be made clear that the danger lies in the interior and people should be better protected. However, this is time-consuming. And although the criticism of the outdoor measures is technically justified, it ignores crucial points.
The objects of study by aerosol researchers are microscopic particles in the air, such as invisible droplets that penetrate our mouth and nose when we breathe or speak. These particles can contain viruses, other people breathe them in, and this is a major way of spreading the coronavirus. The typical indoor currents ensure that even 20 micrometer-sized droplets accumulate in the air. If these come from the respiratory tract of an infected person, the risk of infection for others increases every minute, even if they do not meet the infected person at all, but enter the room after them, for example an elevator. “I wouldn’t go in there now, elevators are very poorly ventilated,” warns Detlef Lohse, who researches the physics of liquids at the University of Twente in the Netherlands. He welcomes the letter from his colleagues.
The risk of infection in the football stadium depends on the wind
Particles behave very differently than in rooms in the open air. There the wind blows them away and dilutes the mixture of air and droplets. These physical phenomena are reflected in epidemiological studies on Covid-19, so researchers from China have tracked infections in the specialist journal “Indoor Air 7324”. They only found one outbreak that began after meeting in the open air. A comparable study from Japan comes to the conclusion that the risk of infection outside is almost twenty times lower than inside. But it is not at zero.
In their letter, the German experts avoid recommendations for behavior outdoors and are satisfied with statements such as: “Wearing a mask in the pedestrian zone and then having a coffee table without a mask in your own living room is not what we are talking about Understand how to avoid infection. ”During an outdoor conversation, someone can spit larger droplets in the face of the person opposite: The dilution no longer plays a role. “In a densely populated pedestrian zone, I would wear a mask, especially when it is wet and cold,” says Lohse. Small suspended particles can also be dangerous. “If you stand at a bus stop and someone smokes, you can smell it more than two meters away,” explains Julian Tang, virologist at the University of Leicester, UK, with a vivid example. Viruses in aerosols would behave in the same way, it just depends on the flow conditions. Therefore, Tang recommends putting on masks in queues and at stops.
In the summer, if the incidence was low, physicist Lohse would sit down on the terrace of a restaurant without hesitation, allow outdoor football training and also let fans cheer in the football stadium, provided they wore masks and enough seats remained free. To investigate how infectious particles behave here, Dutch scientists have positioned machines that generate aerosols on the seats in a block in the Johan Cruyff Arena. They simulated breathing and singing fans in the home of the Ajax club in Amsterdam; Detectors determined how long the particles stayed in the air and whether industrial air purifiers could suck them up. The results are not yet available, but the head of the study Bert Blocken from the Technical University of Eindhoven was surprised by an interim result in the daily newspaper “Trouw”: Above all, the wind influenced the particle concentration, although the stadium is almost closed all around and has a roof .
#Aerosol #research #risk #infection #fresh #air