We have lots of Asians in our area. I get a kick out of them when they wear the surgical masks around town. (Other than the few days/weeks in summer with the fires coming in from Canada - our air is always very clean.) They do NOTHING to keep from breathing in particulates.
They are for keeping one’s own germs from spreading.
But - whatever.
Not true. I lived — and jogged — in polluted Kabul air for over 5 years. After some days I noticed black stuff when clearing my throat. Not good. It was mostly from soot from the wood burned to cook naan (flat bread). But it likely contained airborne feces from the open “sewers” down the middle of the dirt streets.
On my next trip to the USA I got a large box of masks from Home Depot. I began to wear them when jogging. The masks got black and my sputum remained clear. So yeah, they do something.
Obviously they don’t do EVERYTHING as they are like furnace air filters and particles below a certain size still get through.
I live in Asia. We commonly wear masks to work when we have a cold so we don’t spread it. Nice gesture. Not sure if effective.