Aerosol expert: Hardly any corona dangers on the sports field

In an open letter to Chancellor Angela Merkel, aerosol researchers pointed out that the risk of corona infection in outdoor activities is very low. You criticize that politicians do not act accordingly. Sport would want it

Christof Asbach, President of the Society for Aerosol Research, emphasizes that the risk of corona infections outdoors is very low. "It is a certain success for us when people are no longer afraid to go outside and have been made clear where the dangers lurk: inside," he said in an interview with the German press agency.

In an open letter to Chancellor Angela Merkel, the Society for Aerosol Research affirmed that the risk of corona infections is low outdoors and that it takes place indoors. Your society pointed this out back in December and criticized it: “Practical action” by politics had failed to materialize. What does that mean in concrete terms?

We have two goals. One is that this knowledge is translated into action. The second is to educate the population about where the dangers lurk. We have noticed that there is growing concern that you can get infected outside. This was supported by many measures that were also taken regionally, such as the requirement to wear a mask outdoors or the prohibition to stay, which further fueled this concern.

Through the open letter, we noticed greater public awareness than we had before. It is a certain success for us when people are no longer afraid to go outside and have been made clear where the dangers lurk: inside.

If one had already drawn political conclusions from the position paper, club sport could have been reopened on a larger scale long ago, right?

We have thus laid a foundation for understanding that very little can happen outside. Of course, that includes sport. If we don't talk about combat sports such as wrestling or judo, but about team sports or tennis, which were also not allowed and where you don't get close anyway. We see an extremely low risk of infection there. From our point of view, this could have been communicated much earlier. We see the dangers in changing rooms, toilets or when arriving by car or bus. They are not lurking on the sports field.

Sport developed special hygiene concepts for each type of sport early on. Wouldn't it have been possible to continue doing outdoor sports without being interrupted by lockdowns?

That is a question that we also asked ourselves and that was the reason to write this open letter. We have to take an interdisciplinary approach. This is why it is important to hear the virologists, epidemiologists, and ventilators. But when it comes to transmission, the aerosol pathway is the most important transmission route. We are asked to understand how virus-like particles behave. We had the impression that we had not been heard sufficiently.

You write in an open letter: The risk of infection is lower in large halls. Does this mean: is gymnastics in larger sports and training halls actually possible?

It is a question of how many people move in which volume of space. A gym is typically very large. If there are a limited number of people there, I see a relatively small risk because the virus concentration is widely distributed and diluted. Nevertheless, the risk of infection is greater than outside. There are no reasons why you should not allow sport again. In gyms you have to look more critically, but with good hygiene concepts you can reopen them with a manageable risk.

They described jogging with a mask as a symbolic measure. Why?

In order to become infected, you have to inhale a minimum number of viruses. How many I breathe in depends on the concentration and the time during which I absorb a concentration. When jogging and walking, the contact time with other people is extremely short. In addition, the concentration of exhaled viruses is diluted very quickly, especially with a jogger who is on the move. The contact times are short and the concentrations are low. Therefore, the chances of inhaling a number of viruses to infect me are extremely small. The mask requirement is counterproductive because it suggests that there are dangers lurking and that people are more likely to be driven into the interior.

Aerosol particles spread over long distances with air currents and can remain in the air for a very long time. For example, if two joggers run next to each other and gasp: Can't nothing happen?

Of course, the particles can linger in the air for a long time; this applies to both outdoors and indoors. The difference is: In the interior without air exchange, the virus concentration increases continuously. This is not the case outdoors. If you imagine how many viruses you exhale and how much air there is around you, then the concentration is so low that I - if at all - sometimes inhale a virus. A virus does not make an infection. This takes a few hundred to a few thousand.

Christof Asbach is honorary president of the Society for Aerosol Research (GAeF). He is responsible for air pollution control and filtration on the board of IUTA, the research institute for energy and environmental technology.

© dpa Picture Alliance / Rolf Vennenbernd

In addition, there is natural UV rays outside, which means that the viruses are inactivated very quickly. However, a certain residual risk remains in cases where two people stand face to face and talk to each other. Then it can happen that a person inhales the aerosol cloud or exhaled droplets of the other person directly. Sufficient distance should be kept here and a mask should be worn if necessary.

Asking again: If two joggers are running next to each other, is there almost no risk of infection?

Movement alone gives me a lot of dilution. The cloud does not flow directly into the other jogger's respiratory tract.

When cyclists drive close to strollers and joggers: Can this cause virus transmission?

It's the same as jogging, if not more, because cyclists are faster than runners. The contact time is even shorter. And what you feel is not the breath, but the wind or the draft that the cyclist creates. I think it's good when people are alerted wherever dangers can lurk. But this is absolutely no problem for the risk of infection.

Can you get infected in a row eight?

You sit with your backs to each other and you don't get your breath straight into your face, it has to flow around your head and then inhale. In addition, the rowing boat is also in motion, creating a strong turbulence and thus a reduction in the virus concentration. Therefore, I would estimate the risk to be significantly lower than with all activities in rooms.

On the other hand, tennis and golf are ideal ball sports without danger, or is touching the ball a danger?

From an aerosol science point of view, I don't see any danger in a normal game. Not much can happen there. We now know that smear infection, which was initially assumed to be the dominant one, plays a subordinate role.


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