Threads keep coming up where people think they can find a part of HK that is in some magically protected bubble of clean air, despite the several thousand kilometres of Chinese boarder about ten kilometres to the north.
Instead trying to decide where to move within a twenty kilometre square along this border, simply get an air purifier.*
These are shots from a consumer level air quality monitor. Taken this afternoon, about a minute apart. I'll leave you to decide which one is from inside a room with a purifier running, and which is from an outside balcony.
* By purifier, I mean a simple, mechanical one with a HEPA filter and a big fan. Nothing electrostatic, no UV, no magical heath rays. Just a HEPA filter and a fan.