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I was fantasizing about some kind of wearable mask which would create such high speeds of wind that would allow you to breath only the healthy bits of air, as I guess most gaseous compounds which we term pollution are heavier than oxygen.

Anyway: what is the wind speed at which pollution can be separated from air?

You can discuss any range of pollution compounds, depending on a relevant health-related criterion of your choice.

In terms of separation: you can discuss what would be possible in your answer, in terms of changes in concentration over certain distances.

Clarification to object to this question being put on hold: the wearable mask idea was purely anecdotal and not part of the actual physics question. Also: the concept of "wind" should be interpreted merely as velocity of air, not limited to frequently occurring natural wind speeds. If you wish, one can delete the term "wind" and replace it by "velocity". Does this make the question unambiguous enough please? I would be happy to see my question answered for any or multiple common air-borne polluting particles, occurring in metropolis due to the burning of fossil fuels, which are hazardous to our health.

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Take the most common form of air pollution that most people in urban areas encounter, car and truck exhaust "fumes". The size of the particles making up these emissions, especially from diesel engines is summed up here:

Particulate Size Range

The diameter of the original nucleus, such as formed during sulfuric acid nucleation, is about 1 nm [Abdul-Khalek 1999]. Today’s measuring techniques are capable of detecting a minimum particle size of approximately 3 nm. According to various definitions, the diameters of nuclei mode particles are generally less than 40-50 nm (0.04-0.05 µm). Based on particle size research in the 1990s technology heavy-duty diesel engines, it has been postulated that the nuclei mode extends through sizes from 3 to 30 nm (0.003-0.03 µm) [Kittelson 2002][Hall 2001]. All of the above size ranges place nuclei mode particles entirely within the nanoparticle range.

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Distribution of diesel particulates, image source as above.

These particle are not going to drop out of the air at any wind speed, I would guess it is the opposite, they would only settle in absolutely still air.

Worse still is that the masks used to hopefully protect humans from breathing them into their lungs are not airtight around the face, and are not of small enough mesh size to deal with these particles.