The true history of a small mistake that made scientists screw up COVID aerosols

Originally published at: The true history of a small mistake that made scientists screw up COVID aerosols | Boing Boing


Excellent work in digging into the origins of an erroneous factoid, but that it was necessary…



I read this article last weekend, really fascinating. The super-niche overlap of scientists who studied pollution and then virology/infectious diseases was particularly interesting to me. I agree with @RickMycroft , the fact that it was necessary, that this is how the world operates, scream inducing.
It reminded me of some of the numbers we use in building science, related to ventilation rates particularly. When you start digging, you learn that some of them were based on such arbitrary things as the “sniff test,” as in, when would the combined body odor become unpleasant. And those numbers are from the ‘30s, IIRC. :woman_shrugging:t2:


In my career I’ve worked on automating various processes and workflows for biotech and pharmaceutical research.

I’ve repeatedly run into situations where the bench scientist says you have include something that may be particularly difficult to automate because “that’s the way it has always been done,” or “that’s what Protocols in Molecular Biology says to do…”, but no one really understands why or proved that it is essential. In other words, dogma. I’ve found rooting out and working around this kind of stuff is what usually leads to breakthroughs and tangible progress.


This post is written in such a way that it never says what scientists were really wrong about, i.e. aeresol spread is a concern but they didn’t think it was at first. Maybe that’s implied but I had to read the whole post twice and each time felt like a crucial statement was missing.


Reminds me of other small errors that lead to people repeating them as fact for decades if not longer. Like you lose most of your heat from your head.


Or that marijuana is a gateway drug.


On a separate but related note: If you feel like losing a few IQ points, head over to Twitter and watch the conservative freakout over the Fauci FOIA emails.


From the piece:

Trapped in their group-specific jargon, the two camps on Zoom literally couldn’t understand one another.

That sums up so much about the communication failures on this pandemic.

That said, I am totally in favour of using the correct and appropriate scientific wording, related to the specific field. But we need to repeat the definition of our scientific terms over and over again when communicating outside of our sub-disciplines of a scientific field.


Thanks, but…(in the voice of the most interesting man from the commercials), “I don’t always voluntarily lose IQ points, but when I do, I do it with bourbon!”



And no one ever stopped to take a second look at the source of this factoid until the COVID-19 pandemic was already underway.

I appreciate the appropriate use of the word “factoid” as meaning “something that seems true, but isn’t.” People often think it just means “little fact” (although admittedly, that usage is becoming more acceptable as more people use it that way, evolving the language).


This reminds me of the video I watched the other day about how HEPA filters came about. And why they’re effective against things like virus droplets or aerosols.

If you watch that video, you might get an answer to why @tenbrook seems to be confused by the article. The difference, if I understand it right, is that droplets are large enough that their mass is primarily what causes them to move–gravity, inertia, etc.–are the important forces for them. Aerosols are small enough that their mass doesn’t drive their behavior. They tend to move differently because they are more effected by their interactions with gas particles in the atmosphere. That’s the behavioral difference between the two things and why it matters how Covid is classified.


I haven’t re-read the article but, IIRC, the main thing was the arbitrary adoption of 5 microns as the definition of aerosol (based on one particular disease), even though the same scientist found evidence of aerosol spread of other diseases up to the 100 micron level.
So the whole community latched onto 5 microns, and hilarity ensued. /not.


That’s interesting because the HEPA video talks about 3 micron being the threshold between the two different behaviors. I need a scientist in the field to comment now! :wink:


In my residency program, one of the attendings was semi-famous for absolutely destroying any resident whose explanation for why something was done in a certain way was “that’s how it’s always been done” or, even worse, “that’s what Dr. XXX told me to do.” He was kind of an ass in a lot of areas, but in this one he was spot on. We need to know the why if we want to understand the outcomes.


So I went back to verify:

The books Marr flipped through drew the line between droplets and aerosols at 5 microns. A micron is a unit of measurement equal to one-millionth of a meter. By this definition, any infectious particle smaller than 5 microns in diameter is an aerosol; anything bigger is a droplet. The more she looked, the more she found that number. The WHO and the US Centers for Disease Control and Prevention also listed 5 microns as the fulcrum on which the droplet-aerosol dichotomy toggled.

“I’d see the wrong number over and over again, and I just found that disturbing,” she says.
Thinking it might help her overcome this resistance, she’d try from time to time to figure out where the flawed 5-micron figure had come from. But she always got stuck. The medical textbooks simply stated it as fact, without a citation

They bring on a citation tracker/grad student, and track it down to a physician Wells* and his wife in the 30’s:

According to them, particles bigger than 100 microns sank within seconds. Smaller particles stayed in the air. Randall paused at the curve they’d drawn. To her, it seemed to foreshadow the idea of a droplet-aerosol dichotomy, but one that should have pivoted around 100 microns, not 5.

Totally worth a read, quite well-written.
Regarding the HEPA thing, maybe because those particles are under pressure? I’m interested…

*Here’s the curve everything was based on:


I heard a completely different reasoning somewhere. It was that size isn’t a great measurement for defining an aerosol—mass (or was it surface area?) is. A 4-inch long feather will behave differently than a 4-inch long rock. A size range can give a vague approximation, but isn’t great to classify as one or the other.

1 Like

This is a delicate topic because there are evil sub-morons out there attacking the whole concept of expertise and tryna usher in a new dark ages, and their views shouldn’t be alowed a single atom of respect.


It does seem like expert policy advisers did collectively whiff this one thing. Of course no one knew early on how the rona was transmitted, so it made sense to guard against all possibilities, but it was a tactical judgment call to emphasize handwashing and discourage face masks, which now appears to have been exactly the wrong advice, and it’s important for scientists who advise governments to at least ask whether they could have done better.

Something like that isn’t just a matter of science. If you don’t have enough data to answer a question, then that’s all you can say as a scientist. If you’re pushed to give your best guess, fair enough, but even a qualified scientist’s guess isn’t science – it’s subject to questions of ego and politics and other stuff that scientists aren’t generally experts in.

The initial estimate was that cloth masks wouldn’t help much, and there’s no blame there (even if your evidence ends up being wrong, you con only go by the evidence you have). And because there was a fear of mask shortages for healthcare workers, the decision was to tell the public not to wear masks. But it wasn’t long before the data suggested both those premises were wrong, and for a long time after that I was hearing experts (at least in the UK) resisting the suggestion that their advice was wrong. Which is understandable on a human level, because they’re fighting to get even their most basic advice accepted, but still: it’s likely that fewer people would be dead in the UK if the advice had switched to “wear a mask everywhere” in the summer of 2020. To this day, mask wearing is half-hearted in the UK, and folks are still much more concerned about hand sanitizer.

As an architecture undergraduate, I was specifically trained to separate my ego from my work (using similar techniques to Maoist struggle sessions). But in my previous life I was a bad chemistry student at Imperial College, and while I would trust those people on questions of science, I can tell you that dealing with human issues is not what they’re trained in, and in most cases not their natural forte. I don’t know if the answer is for scientists to be better trained in public policy, or for politicians to be better at synthesizing scientific advice, but I’m pretty sure there is a bunch to be learned from this whole covid thing.