Ten out of TEN

[Jace]

According to the World Health Organization, the recommended safe limit for PM2.5 particulate readings is 25.
In the part of China I live in, we regularly had readings over 300 last year, with several days above 500 and even one of 600. Although the schools had to close down and people were told to stay indoors, most people of course had to go to work etc, so masks of any thickness were the order of the day.

This is another reason (in addition to epidemic) that I am stocking up on face masks. I only have the cheap disposable ones at the moment, but will be looking to stock up on the industrial ones soon when I have some cash.