The aerosol discussion is a thing of the past in the scientific world, as evidenced by the medical follow-up studies on the generation of aerosols. I came across a study that shows that singing and speaking generate many more aerosols than coughing and sneezing. When coughing/sneezing, the large droplets, which were traditionally seen as the main contaminants, end up on the ground within one and a half meters. The small, almost weightless droplets, which are mainly released when speaking and singing, float longer, ready to be inhaled.
Curious about how aerosols are actually created, I ended up with nebulizers. These are used, for example, in inhalation equipment. One type, the ultrasonic nebulizer, has remarkable similarities to vocalizations. The similarity is so obvious that I wonder why everyone is so obsessed with falling droplets within one and a half meters, sneezing, 'coughing' - while simply speaking - and certainly singing - might produce more aerosols? That can't be true, can it? Maybe so. First a simple explanation of atomization or aerosol production, then the reference to the science behind it.
Aerosol production
Nebulizers and inhalers (unless they spray powder, which is also possible) must convert liquid into droplets small enough to inhale. There are different systems and devices depending on the application. The basics are the same. It often starts with sound vibrations. ultrasonic, so we don't suffer from humming or squeaking. So:
- aerosols are vibrated with sound vibrations (singing/resonance are also sound vibrations)
- pressure is built up to spray them outwards (pressure on diaphragm, squeezing vocal cords)
- the aerosols are squeezed out through a (too) small opening or narrow slit to 'atomize' them (glottis)
Due to the desired volume, the breathing pressure is increased and breathing is deeper and 'from the belly'. I assume less superficial breathing, more from the lower airways. That is precisely where the biggest infection problems arise.
Remember that in (group) conversations you generally speak one at a time. When singing and cheering, dozens (hundreds) of people can be 'speaking' at the same time, at volume and breathing deeply. This means a many times greater aerosol production. Do this in poorly ventilated spaces and it is not surprising that you hear relatively much about infections via choirs and churches.
(EDIT for Maarten Keulemans: Natural ventilation is poor ventilation if there is not enough wind. What counts is the 'ventilation rate'. That must be much higher for a choir than for an office space. I hope I don't have to calculate that.)
Nice hypothesis, so I googled it and yes: virologists have known it for a long time! (Not in the Netherlands of course, but elsewhere it is). This article from February 2019 confirms this and contains several links to previous research on aerosols and the importance of aerogenic spread in infectious respiratory diseases.
Below are some facts from the article https://www.nature.com/articles/s41598-019-38808-z , where they Comparing coughing, sneezing, speaking and singing in terms of aerosol emissions. It goes without saying that aerosol clouds can cause infections, as has been shown in countless other studies. As long as this is not accepted by WHO and RIVM, it will continue to fight a losing battle in the Netherlands, mopping up with the tap open.
It could also explain why the Japanese colleague of Prof. Dr. Voss was unable to obtain a good aerosol sample, just in front of the mouth of a corona patient. If only that patient had made him sing a piece...
[EDIT 31-10: By the way, it is now others managed to sample 'viable' SARS-Cov-2. (opens in new tab) ]
Fun facts
- The louder the voice volume, the more aerosols (think of environments with loud music such as après-ski, carnival)
- singing generates 6 times as many aerosols as normal talking
- Singing for 10 seconds produces as many aerosols as a 10-second coughing fit
- 30 seconden hoesten staat gelijk aan 30 seconden "aah" zeggen
- some people generate noticeably more aerosols than others when talking. The cause of this is not yet clear. Such people will therefore have a relatively large share in superspread events.
- A good face mask minimizes the emission of large and smaller droplets and reduces aerosol emissions. [edit: Approx. Reduces by max. 10% with the most common face masks]
In any case, aerosols pose a more significant risk of infection than larger sneeze and cough drops, because
- they remain in the air longer so have a greater chance of being inhaled
- the smallest droplets travel more easily deep into the lungs where they cause more serious infections.
By the way, all of the above statements come from the report of the study in Nature, I'm really not making it up myself.
'Soft g' vs 'Hard g'
In this context this recent article ook aardig. De Engelse klank "th" genereert de meeste druppeltjes van alle klanken (je ziet in de video alleen de druppeltjes die deze camera kon registreren, ik neem aan dat microscopisch kleine druppeltjes niet gefilmd zijn). Ik ben benieuwd wanneer het RIVM erachter komt dat een 'zachte g' fijnere en dus gevaarlijkere aerosolen genereert dan de 'harde g'... maar dat heb ik dan wel gewoon zelf gefantaseerd 🙂 .
Anyway, last night there was another corona press conference with Rutte and De Jonge. The word 'ventilation' didn't even figure in it. It makes me desperate.
