What everyone should know about aerosols

There is a strong scientific consensus on the major responsibility of contaminating aerosols in the transmission of SARS-CoV2. These aerosols consist of fine particles suspended in the air, carrying viruses, which can persist for a long time in a closed space after being emitted by an infected subject, even if he does not cough.

Diffusion of aerosols in the air

Almost everyone has heard of these aerosols, but the following information does not seem to have been properly assimilated:

Let's go over these elements in detail:

Contaminating aerosols persist for a long time in an enclosed space

The finest particles emitted by infected subjects are very light and float in the air. In addition, they have the ability to penetrate deep into the lungs of healthy subjects who inhale them. They are therefore particularly dangerous. A completely closed room can remain contaminating for a very long time, including after the departure of the contaminating subject.

A simple experiment can be convinced of this: pour a teaspoon of fine sea sand into a glass. A few minutes later, the water has become clear again and the sand is at the bottom of the glass. Sand, even fine, is made up of large particles. Repeat the experiment with a teaspoon of muddy water. If you wait several days, the mud will settle at the bottom of the glass and the water will become clear again; but an hour later, the water is still charged with fine particles in suspension which make it opaque. The suspension of fine particles in water is a phenomenon physically comparable to an aerosol.

The grains of sand correspond to the sputters emitted by a cough or a sneeze. They quickly fall to the ground. The clay particles of the mud correspond to the fine invisible particles emitted by speech or even simple breathing; it is these fine particles that constitute the persistent and contaminating aerosols.

Standard masks do not protect 100% and even less if they are removed...

We rightly insist on the protection provided by the surgical mask, but this protection is modest and therefore does not provide total safety. First, these masks are rarely applied correctly and side or nose leaks are common. This does not lend too much consequence in the event of brief exposure, in a store for example. But during a reunion with family or friends in a closed room, the inhalation of a contaminating aerosol for several hours through these leaks is sufficient to cause an infection.

The worst risk of contamination is linked to a belief that is as absurd as it is widespread "if I wear my mask 90% of the time at a party, I am 90% protected"! No, it doesn't work! If you regularly take off your mask to eat, drink or smoke in an unventilated enclosed space, it's almost as if you hadn't worn a mask! The strength of a chain is limited to its weakest link.

It's not just people who cough that are contaminating

Speech, shouting, singing, emit a considerable amount of particles. Several cases of massive contamination of choirs have been reported, including in churches where the volume of air is large. The height of the ceiling can give the illusion of safety linked to the dilution of aerosols in a large mass of air. In fact, aerosol particles are often concentrated at head height and tend to sink slowly if they are initially carried up into large rooms.

Air exchange is a major factor in the removal of aerosols

It's primordial ! There are aerosols like cigarette smoke (which is an aerosol with the particularity of being visible): it is necessary to ventilate to eliminate them. But to ventilate means to create a movement of outgoing and incoming air. Opening a window is often insufficient. You need a current of air crossing the room, that is to say at least two open windows, on different facades of the house or the building so that the wind ensures a real mixing of the air. A good marker of the renewal of the air in a room is a CO2 meter (emitted by our breathing). An acceptable threshold is 800 ppm ("part per million"), but 600 ppm is even better. As soon as the threshold is exceeded, the ventilation of the room must be increased. Good quality devices are available for less than 100 euros2]. If you can afford it, the investment is very worthwhile.

Be careful not to confuse with a CO detector (toxic carbon monoxide), cheaper, but which has nothing to do.

Outdoor activities are little or not contaminating

Due to the mixing of the air which prevents aerosols from stagnating, outdoor activities are not contaminating in the vast majority of cases. Only compact crowds or motionless gatherings in highly contaminated areas (queue in front of a hospital or laboratory) could expose people to a significant risk. Outside, it is enough not to be on top of each other and to speak more than 50 cm from your neighbor to protect yourself. The mask is not necessary.

If you decide to meet in numbers and without a mask despite the ban, do it outside and don't get too tight! It changes everything!

That's it, it's very simple but absolutely essential. I am convinced that if everyone understood these basic notions and took them into account whenever possible, the epidemic could be stopped.

I hope that the good weather that will eventually arrive will change the situation and that we will stop disturbing people's minds with inconsistent measures such as the obligation to wear a mask on the beaches. You have to keep your authority for the important things!

To know more

the importance of aerosols revised upwards. Sylvie Logean. The weather. 2020Covid-19: aerosol diffusion, a greater threat than the WHO supposed. Byron Erath, Andrea Ferro, Goodarz Ahmadi. The Conversation. 2020 Mechanism of airborne transmission of infectious agents. Elizabeth Bouvet. 50th day Claude Bernard. 2007 How to choose your CO2 detector. On the side of science. 2021

Spread this article, copy it, make videos of it! Anything that will disseminate this vital information will contribute to the fight against the epidemic

Since the publication of this article, a summary in English on the subject has been published by the American journal Science. It is a remarkable document that should be read (with the help of Google Translate if necessary) by anyone wishing to protect themselves from this virus in addition to vaccination)