>>I agree with everything you posted. Still, a mask worn correctly does limit the spread. For example, the spread of the virus on airplanes seems to be (surprisingly) much lower than initially feared. I think that is in no small part because of the more disciplined attitude of most travelers in wearing the mask and applying proper hygiene measures.
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>It also helps that the air in an airplane is not circulating. It flows in and out. Or am I wrong here? Or it's the heating...?

>One thing I proposed once never got off the ground, so let's give it another try. The UV lamps should sterilize the space - they keep them on in surgery when there's nobody inside, right? So okay, you can't use them on shopping malls, but why not install them in AC ducts? There's nobody there, and it seems that's exactly the place every virus or bacterium visits frequently, so why not ambush them there?

From what I've read, on airliners, there is a complete volume exchange of air with the outside every 2-3 minutes. In the meantime, the air is circulated through HEPA filters. They use UV wands to sterilize the inside between flights, not sure why they wouldn't use it in the AC ducts. Perhaps, the current system is good enough.