Funny, before the cruise of Chinese port cities last fall, I bought N99 masks for the same reason.
Yes, N99! They were made in the UK cost about $30 each. Didn't really use them on the cruise because the pollution in port cities was not that extreme.
We're using those masks now when we go for the occasional shopping for food.
Alex
"There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "my ignorance is just as good as your knowledge."
-- Isaac Asimov