This is commonly stated, but untrue. Here are a couple of studies on this topic. [1] [2] And the always critical third link. [3]
The nature study carried out specific tests and indeed surgical masks did surprisingly very well at blocking particulate matter all the way down to 1 micrometer, with a significant effect on much smaller particles as well. PM2.5 = 2.5 micrometer / 2500 nanometers. The NIH study compared the health effects of individuals with/without masks in everyday activity in Beijing.
I think the assumption is that if the particulate matter is smaller than the size of the 'gaps' within a mask then it would be ineffective. I always just visualize a simple experiment. Imagine shooting a stream of particles of a given size at a wall. Now interject a 'net' of practically any size. Now interject multiple 'nets' (as is the case in typical surgical masks). It becomes clear that even quite large large filters will have a non-zero effect on stopping matter far smaller than the max size that can make it through.
In Vietnam most don't wear surgical masks. We use fabric ones generally out of cotton.
They do protect against larger dust particles while driving, which is why I wear them, but as said above, Vietnamese mostly wear them to protect skin from the sun. The higher quality masks are really just too hot to wear as they do not breath enough.
There is something called a Lead Ninja, which is a woman on a typical motorbike (Honda Lead), dressed head to toe completely covered... to the point that driving is dangerous because they can't even see where they are going. There was a funny blog post about driving etiquette here a while back [1] that is sadly pretty spot on.
What gets me is the general lack of wearing eye protection while on a motorbike... not only do your eyes dry out more quickly, which affects vision, but the dust and bugs getting into the eyes makes driving almost unbearable. I don't know how they do it here. Solution is literally $0.85 clear plastic glasses found everywhere on the street.
huh after experiences otherwhere in Asia, Vietnam is very void of bugs, compared to Thailand for example. Someone told me it's mainly because of napalm in the war. Who knows
My experience is that it is because of the high number of swallow bird houses.
If you drive around (I've driven most of the southern end of VN and Cambodia), the multi story, windowless buildings are everywhere and in towns with a lot of them, far fewer bugs. The Vice article quotes 4200 houses... my guess is that it is 10x higher than that.
I'm currently in Hoi An and there is a ton of bugs here and not as many bird houses.
Pure anecdote, but when I was visiting Vietnam (Saigon and Can Tho) recently, I would go up to the rooftop balcony in the evenings and watch the birds and then bats out hunting their (insect) dinners. It stuck with me, because the numbers of birds and bats seemed much higher than I would normally see in the urban Midwest here in the US.
The nature study carried out specific tests and indeed surgical masks did surprisingly very well at blocking particulate matter all the way down to 1 micrometer, with a significant effect on much smaller particles as well. PM2.5 = 2.5 micrometer / 2500 nanometers. The NIH study compared the health effects of individuals with/without masks in everyday activity in Beijing.
I think the assumption is that if the particulate matter is smaller than the size of the 'gaps' within a mask then it would be ineffective. I always just visualize a simple experiment. Imagine shooting a stream of particles of a given size at a wall. Now interject a 'net' of practically any size. Now interject multiple 'nets' (as is the case in typical surgical masks). It becomes clear that even quite large large filters will have a non-zero effect on stopping matter far smaller than the max size that can make it through.
[1] - https://www.nature.com/articles/jes201642
[2] - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2662779/
[3] - https://sci-hub.tw/