Warum die Virenkonzentration bei zu trockener Raumluft zunimmt

Winter is considered the time of infectious diseases. This is also because the concentration of viruses in closed rooms often increases. Air that is too dry encourages this and is therefore one of the causes, as is infrequent ventilation. If you want to reduce the risk of illness, you should ensure that there is sufficient humidity and air exchange. According to the Institute for Tropospheric Research (TROPOS) in Leipzig, this also applies to the coronavirus 1 . But why is that?

Viruses spread through the air

Viruses are spread in different ways. One of the transmission routes is so-called smear infection. For example, someone touches their nose with their hand and wipes off nasal secretions that contain the virus. They then touch a door handle with their hand and transfer the virus there. Another person also touches the handle with their hand and then touches their lips or nose. This is how they become infected. To prevent this, great importance is placed on disinfected surfaces (not only) in the fight against the coronavirus.

Someone sprays door handle with disinfectant spray - Reduce virus concentration through disinfection
© fotograf-halle.com – stock.adobe.com

Droplet infection is at least as important a method of transmission. It works with larger viruses over a short distance. Someone sneezes. This means that tiny droplets containing the pathogen may travel from the sneezing person to another person. The person who is sneezed on often doesn’t even notice it, but they become infected. To avoid this with the coronavirus, rules apply such as the requirement to sneeze into the crook of the arm and the requirement to keep a distance. Droplets containing pathogens do not fly much further than one meter in this way. With smaller viruses, however, so-called aerosols can come into play.

Woman sneezes - viruses spread, symbolic image - virus concentration is high when sneezing
© metamorworks – stock.adobe.com

Another transmission route: aerosols in the air

Aerosols are another way of transmitting viruses. They are also virus-containing droplets, i.e. a mixture of liquid and solid components. However, aerosols are much smaller than the droplets transmitted over a short distance by sneezing. They can therefore float in the air for a while and, in the worst case, cause a permanently high concentration of viruses in the room. They are called aerosols because of this property.

Aerosols can apparently also transmit the coronavirus 2 . In a study by two US universities and the National Institutes of Health in the USA, the virus survived in aerosols for up to three hours 3 . It may therefore be necessary to develop strategies to ward off Covid-19 in aerosols. This is often even more true in winter than in summer. One important reason for this is the dry, heated air in winter, which can be partly responsible for an increasing viral load in the air. The viral load is the concentration of viruses in the room air.

Aerosol with virus, drawn picture
© Alexander Limbach – stock.adobe.com

Dry indoor air increases the virus concentration

In winter, the air in indoor spaces is often very dry, also known as heated air. This can significantly increase the aerosol concentration and thus the virus concentration in the air. The reason for this is obvious: in humid indoor air, the aerosols are enriched with water due to the high humidity. This makes them heavier and sink to the ground more quickly. This reduces the aerosol concentration in the room and thus the risk of inhaling the viruses. In dry air, the finest droplets dry out more quickly, but this does not completely compensate for the disadvantage that they float longer.

Young woman puts cream on her hand
© Antonioguillem – stock.adobe.com

Humidity could also play a role in the spread of Covid-19. This is at least the case according to an analysis of ten international studies conducted by the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig and the CSIR National Physical Laboratory in New Delhi. These scientific teams also pointed out the effect that the virus concentration can possibly be reduced in humid indoor air due to suspended particles sinking more quickly. In addition, TROPOS emphasizes that other factors such as fresh outside air also reduce the risk of transmission.

Reduce high virus concentration: increase humidity!

The TOPOS advice already outlines the path that should be taken to reduce the concentration of viruses indoors: ensure air exchange and increase humidity. Houseplants, aquariums or drying laundry can increase humidity, but so can small humidifiers that can be hung on the heater. Electric humidifiers are even more effective . Small models such as the B 120 or B 125 from Brune are sufficient for private homes.

Humidifier B 125

However, if the aim is to humidify dry air in open-plan offices , libraries, museums or large industrial plants, more powerful models are required. The Brune devices B 250 or B 500 Professional are suitable for this. Both humidifiers can also be equipped with UV disinfection. Both devices can run in automatic mode and start automatically as soon as the humidity falls below a certain limit. If the humidity rises above the minimum value again, the devices stop.

The air exchange must be sufficiently frequent

Due to the importance of fresh air for reducing virus concentrations, it is important to ensure sufficient air exchange. This ensures that polluted room air is replaced with fresh air. In modern and particularly airtight new buildings as well as in extensively renovated buildings, ventilation concepts ensure that this air exchange is guaranteed. The concepts sometimes rely on technical solutions. But here too, manual window ventilation is not necessarily completely replaced.

The classic tips apply to window ventilation:

  • During the winter months, you should briefly ventilate your room three to four times a day, before turning down the heating.
  • From December to February, each ventilation cycle should take approximately five minutes.
Open window in winter
© mreco – stock.adobe.com

If you pay attention to both air exchange and sufficiently high humidity, you have a good basis for reducing the risk of high virus concentrations indoors.