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I don't see what was incorrect about the parent.

It goes on to say "However, there are microdroplets which stay in the air for 30+ minutes depending on the air currents."

It sounds like you're both in agreement that large droplets fall quickly to the ground, and that with COIVD the longer-lasting micro-droplets are a relevant factor.

Am I missing a subtlety?

There are no "microdroplets" which stay in the air for "30+" minutes.

First, water DRIES OUT unless the humidity is very close to 100% which is relatively rare in western countries. The smaller droplet the faster this happens.

Put a very, very small droplet on a flat surface like glass. Observe it disappear within couple of minutes. Then imagine that a smaller droplet is just larger droplet closer to drying out.

Volume increases with cube while surface with square of diameter. When the droplet gets smaller the drying out speeds up.

The only time there are persistent droplets of water in air is called fog and happens when air is supersaturated with water. This happens when you cool air that is already 100% humidity. In that circumstance water cannot evaporate and that is what makes it possible to have water droplets in air. Once the relative humidity falls below 100% even a tiny bit, the fog almost instantly disappears.

Ability of virus to be airborne means it can survive outside droplet of bodily fluid for an extended period of time. Once all water dries out it also becomes very light and can be moved by smallest currents of air.

I suggest you educate yourself on the topic of microdroplets.

https://www.weforum.org/agenda/2020/04/coronavirus-microdrop...

I suggest you educate yourself.

https://en.wikipedia.org/wiki/Airborne_disease

"Airborne transmission is distinct from transmission by respiratory droplets. Respiratory droplets are large enough to fall to the ground rapidly after being produced (usually greater than 5 μm), as opposed to the smaller particles that carry airborne pathogens. Also, while respiratory droplets consist mostly of water, AIRBORNE PARTICLES ARE RELATIVELY DRY, which damages many pathogens so that their ability to transmit infection is lessened or eliminated."

Here, I capitalized it for you so you don't miss it.

Airborne virus is what happens after fine respiratory mist dries out, which happens quite quickly. It is "relatively" dry because some of the respiratory fluid is hygroscopic. Don't make a mistake, there is no free flowing liquid with virus happily swimming in it.

Thank you, you're repeating things I've already stated in my first post. I suggest reading things more carefully.

In your refusal to read the article, you're missing how sars-cov-2 is teaching us new science about how viruses may survive in aerosols, which behave differently from particles that travel in a ballistic motion.

Airborne viruses have been known for a long, long time. The physics is established. The whole reason we distinguish between airborne and non-airborne viruses is exactly because virus needs special arrangements to be able to survive outside of fluid.

While it is interesting how particles move in a room, it is completely different topic. The particles ARE NOT AEROSOL. The kind of aerosol that can flow in tiny air currents dries out in seconds and becomes small particles (not droplets) of "relatively dry" matter that is fine enough to stay in air for a very long time.

These threads are awful because "droplet" and "aerosol" don't have good fixed definitions, and because people misuse the word "airborne" to mean "aerosol".

Yes, there is a lot of education problem when you want to discuss anything virus related.

Aerosol == small droplets of water.

Airborne, particles == no droplet, just leftover of an aerosol that dried out in less than 100% humid air.

It would not be the first time that health-related article on an economic website gets physics wrong.

I appreciate the distinction you're making here. I don't have enough facts to prove or disprove it.

But, I'd like to ask: are you suggesting that aerosolized droplets cannot be seriously spreading this disease because they will evaporate almost instantly?

I ask because there is quite a bit of research suggesting that aerosolized droplets are spreading the disease, and can hang int the air for a substantial period of time. Do you think this is wrong? If it is wrong, why do you believe people are suggesting aerosolized transmission?

Well... I am not suggesting anything.

There are two types of viruses: airborne and not airborne. Airborne can survive for some time outside bodily fluids.

Aerosol == bodily fluid that is still liquid. It is just in the form of very small droplets that are now drying out. Depending on conditions this lasts very shortly. It spreads the virus, of course, but aerosol dries out quickly and viruses that are not airborne die (well.. viruses do not live in the usual sense, basically their proteins get damaged).

Of course if somebody coughs in your direction some of the aerosol can be inhaled or reach your retina or get on your hands and you can get infected.

No, I am not suggesting droplets cannot spread the disease, the opposite is true. Droplets are much better transmitter of disease if they can reach the target.

True. And I am curious whether things can be done in most building's HVAC systems to account for this.

The ideal would be:

- Heavy external air exchange OR heavy filtering (think N95-level filtration on the return air exchange

- Diffusers are at foot level (not common)

- Return air in ceiling

- People wear masks

My fear of school spread is that folks are basing their mental models on the flu, and if this hangs in the air for an appreciable amount of time then classrooms are difficult to keep sanitized.

Good luck out there. Thanks for the knowledgeable comment.

"However, it seems COVID has an above average ability to survive in extremely fine droplets - think mist-sized particles that CAN float in the air for an extended period of time (given the right circumstances)."

This is one of those "facts" that is often repeated, but which has little actual evidence if you bother to look for it. The WHO has been consistent that aerosol transmission of the virus is a theory with little backing evidence:

Some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants, or in fitness classes. In these events, short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out. However, the detailed investigations of these clusters suggest that droplet and [transmission from contaminated surfaces or objects] could also explain human-to-human transmission within these clusters."

"Current evidence suggests that SARS-CoV-2 is primarily transmitted between people via respiratory droplets and contact routes – although aerosolization in medical settings where aerosol generating procedures are used is also another possible mode of transmission"

https://www.who.int/news-room/commentaries/detail/transmissi...

ARS did a pretty good job of summarizing the (IMO terrible) mass-media reporting on this issue:

https://arstechnica.com/science/2020/07/no-the-who-has-not-r...

> although aerosolization in medical settings where aerosol generating procedures are used is also another possible mode of transmission

I'm married to a physician and have been primarily following this through the eyes of her and her peers. In an acute care setting, aerosolization is a huge concern. It's a big factor between being able to get away with a surgical mask/face shield and requiring significant PPE.

In daily life, this probably isn't a huge concern (or a significant means of transmission at a public health level).

Sure, absolutely. If you're in the business of intubating people on a daily basis, then it's a real concern.

This is what the article challenges.

The author provides cases of events where infection by droplets cannot entirely explain the spread.