Investigation: Corona floats in air for minutes, so open windows

The good news: large drops of saliva drop to the ground in one second when talking or coughing. The bad news: the small droplets take a long time. Sometimes as long as five to ten minutes. And that also applies to the drops of saliva that contain corona.

Daniël Bonn, professor of physics at the University of Amsterdam, is one of the scientists who participated in the major research in recent weeks. To see, measure and count the droplets, the researchers used a special new laser technique. Bonn and colleagues published their findings today in the scientific journal The Lancet Respiratory Medicine.

Tens of millions

“This concerns tens of millions of small, light droplets that we emit when talking, coughing or sneezing,” explains the professor at RTL Nieuws. The droplets cannot be seen with the naked eye.

“This means that in interior spaces and, for example, public transport, you are unknowingly at risk of becoming infected for minutes if the person who has talked has corona.” In addition, apps that keep track of contacts with other people, for example, are not enough in the fight against corona, the scientists say. This is because the droplets are therefore still present minutes after contact.

And now?

The research is new, Bonn says, as are the results. “To my knowledge, the laser technique has never been used before. Only colleagues in America have carried out the same type of research so far, and they also came up with the same results.”

What does this mean in our fight against corona? The professor is clear: “Ventilate, ventilate and again: ventilate. That is the most important and even crucial to prevent people from becoming infected in indoor areas.” He states that it is just as important as keeping a meter and a half away.

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According to the university, the results of an experiment in a well-ventilated room improved drastically. After a ventilation system was activated, half of the droplets disappeared from the air in 2.5 minutes. The same study found that in a room that also had a window and a door open, the number of droplets had halved even after 30 seconds.

So also at the office

So also in offices and in gyms, sports halls, classrooms where the air conditioning is on, preference is given to doors and windows open. “The droplets do little harm outside, because they are diluted with the outside air at a rapid rate. But inside it is a different story,” says Bonn.

Especially if the air conditioning inside is bad, people can get in together no time to contaminate. “We saw that, for example, with research into contamination in a restaurant in China. There the air conditioning did not have good filters, so that the contaminated particles simply continued to circulate through space.”


Bonn emphasizes that there are now many companies that work with good air conditioners. “That is very nice for the temperature and the indoor climate, but we now know thanks to this research that it is not the best way to combat corona infections.”

“Then you really have to open everything old-fashioned. Let it air.”

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