"Aerosols, Droplets, and Airborne Spread: Everything you could possibly want to know" by Justin Morgenstern, MD.
A couple of excerpts : "Large droplets drop to the ground before they evaporate, causing local contamination. Disease transmission through these large droplets is what we often refer to as “droplet/contact spread”, where disease transmission occurs because you touch a surface contaminated by these droplets, or get caught within the spray zone when the patient is coughing. Aerosols are so small that buoyant forces overcome gravity, allowing them to say suspended in the air for long periods, or they evaporate before they hit the floor, leaving the solid particulate (“droplet nuclei”) free to float very long distances, causing what we often refer to as “airborne” transmission."
"We need to distinguish between possible and likely. Airborne transmission of influenza and COVID-19 is clearly possible, and probably does occur occasionally, but we also have to acknowledge that it is very rare. How can we know that it is rare? If airborne transmission was highly likely, we would see much bigger outbreaks. There have been thousands of COVID patients managed in normal hospital rooms, or behind curtains, and not every person in that department gets sick. Similarly, there have been many sick COVID patients on planes, and although there is some transmission, most people are fine. I think that message is key. Airborne spread is possible, but if there was a COVID patient coughing without a mask on the other side of the department, it is still very unlikely you will actually catch the disease, even if you aren’t wearing PPE. You are much more likely to catch it from droplets or close contact, which is why infection control practices are so focused on those activities.
If you are a numbers person, people have done some calculations. There are a lot of assumptions, but the best estimates are that if you spend 15 minutes in a room with a coughing patient, your chance of catching influenza from large droplets and self inoculation (contact) is about the same (and not very high). Transmission through airborne aerosols is about 100 to 1000 times less likely than the other two routes (Telllier 2009)
That is reassuring. However, it is a mistake to take that line of reasoning too far. Just because droplet spread is more likely, doesn’t mean that airborne spread should be ignored. It is wrong to categorically say that COVID does not spread through an airborne route.
The focus should be on droplet and contact spread. At the same time, we should not ignore the airborne route."