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The risks of air conditioning

About aerosols, masks and RIVM - 9363
Samenvatting van het artikel

I get a lot of questions from various countries where outbreaks are difficult to explain. I've talked to infected people in these countries and also looked at the weather developments there. I've spotted an interesting pattern which I will share in this article. These conclusions aren't watertight just yet.

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The risks of air conditioning

I get a lot of questions from various countries where there are outbreaks that people don’t understand very well. Or that are assigned to the wrong cause (e.g. ’the beaches are open again’ ).

I’ve talked to infected people in these countries and also looked at the weather developments there, to spot an interesting pattern, worth sharing in advance (although these are not water tight conclusions yet)

With regard to poorer people in the (sub)tropical areas, there is a clear relationship with rain/thunderstorms.  People who take shelter inside together may turn off fans, thus creating the optimal conditions for a large number of people to be infected.  This is described here.

(Based on the advice of one of my readers I can best call this superspreading circumstances instead of superspreading events)

It can go wrong

But another factor also plays a major role in these areas: the use of air conditioners. If they are used at home by a small number of people who are with you regularly, it seems to be less of a problem. But if more people than usual are present who stay there for a relatively long time at a relatively low temperature, and there is someone present who – without knowing it – is contagious, then things can go seriously wrong.

Be aware that the outbreak at the wholesale centre in Beijing took place in the meat and fish department. Typical departments where the temperature is kept forcibly low, just like in slaughterhouses.

But when does it go wrong when using air conditioners?  Always or under special circumstances? It seems to be more the second than the first in tropical areas.

For example, when I looked at Miami and Austin, where there are also clear rises, I noticed quite some rain and thunderstorms in recent weeks.  These are the moments when a relatively large number of people are staying indoors. Various scientific sources explained to me that before a thunderstorm, something happens to the electrical charge in the air. 


According to that information, this could affect the way aerosols behave in the air. At high humidity the problem of aerosols would be much smaller than at low humidity (typically caused by air conditioners). But it could be that with a certain electrical charge of the air, this process is different than when there is no thunderstorm in the air.

Ventilation remains the most important thing to do. Wear masks inside if it’s not otherwise possible to keep distance in order to breathe out less viruses, if you shelter a few hours inside with a large group of people and divide as much as possible over the available rooms/spaces. And in all cases, don’t stay too long in an environment where you risk indeed breathing in the virus for quite some time.

In addition, in searching for possible explanations of the above in countries where Islam has a prominent presence, I have also seen clear relationships between the Sugar feast at the end of Ramadan and the increase in the number of cases from about five days later, at the end of May (as in Iraq). These are countries where the air is usually much drier than in most subtropical areas. 

This alone in combination with air conditioners can lead to circumstances where people can be more easily infected by the virus in the air. That seems to me to happen when a lot of people are together and not so much in their own home with just their own family.

Important condition

However, it is important to realize that there must be an important condition for air conditioned outbreaks: that there are people present who can infect others. In the countries of Western Europe, I think that in the next two months those risks will be significantly less than in the countries where the outbreaks have now started, because of the wet season (such as in South America and India).

Hopefully this will help reduce the chances of infection. If you know why, you know what you can do about it.

You have just read: The risks of air conditioning.

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