In this simple Stokes law calculation, the distance scales with 1/R², so larger droplets go farther (more inertia). So a lot depends on the size spectrum.
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Replying to @gmusser @DrPascalMeier
Of course if you are hit by larger gobs you are also more prone to notice. When small droplets evaporate before they hit the floor, the virus may stay in the air and waft around for a while.
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Also, Stokes's law assumes rigid spheres. Larger droplets may assume a more aerodynamic shape. Smaller ones may be carried further on air currents. I'd want to know more about both before relying heavily on the simple calculation if my life is on the line! (It may be—so I do!)
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Here’s a chart of the Stokes law calculation. Yes, Stokes law is an approximation and misses much. My main point, though, is that I think the 2m guideline is based on such a calculation, and it is very sensitive to assumptions about size and initial speed.pic.twitter.com/xCmTcebzJK
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I would expect it to be based on measurements, together with some assumptions about dose-response. Here's a 1946 paper...https://www.evernote.com/l/AA-nLB2pBwdNuqPL5_146bOu3ofO8xbLP4U …
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As to dose-response, I think data is limited. Here's a study on that wrt influenza, but I expect it's disease-specific and dependent on the route of entry.https://www.sciencedirect.com/science/article/pii/S1755436510000605 …
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Of course, the existence of studies doesn't demonstrate they were actually used in creating policy guidelines. But I think if you go to the trouble of finding the particle size distribution, you'd find studies covering the distances they travel.
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It's reassuring (and interesting) that Stokes gives similar results. It just seems to me a superficial approach to something that needs more real-world data. But I hate scalars. I want an infection PDF across multiple dimensions!
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And right on cue, today's LA Times on apparent aerosol transmission in WA.https://www.latimes.com/world-nation/story/2020-03-29/coronavirus-choir-outbreak …
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How awful. What sets the time that aerosols are suspended? It’s not gravitational settling, I presume.
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Yes, this is really worrying to me, and might explain why it was so hard to get the infection rate down in Wuhan. And why China blew disinfectants into their streets. You may have to wait until the air is sufficiently diluted, or until the virus becomes inactive?
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