Surgical masks : completely useless against the microscopic particles that do you the most harm.
Air purifiers : Yes, the good ones ( 12-14000HKD each ) work well in bringing down the particle/litre to below 60K, the IQ air, running 24/7 can bring the PM/litre down to below 10,000 which is good, but you have to leave the apartment sooner or later.
Stay indoors : Bah ha ha ha, the stupid, inane, pathetic HK government tell you to stay indoors on really bad days where the air quality is almost EXACTLY the same as outside ( unless you have air purifiers ). Are people really that stupid to think their flats ( especially here ) are air tight
Commuting : People do, from Thailand, NZ, Oz, even SA etc, there are many financial penalties, visa/living issues of course and eg Thailand you/your family have to leave every few months.
Basings : depending on who you talk to at CX, these could become extinct, at the moment tho I think Oz bases are not that hard to get bearing in mind you will be an S/O for 4-5 years and then JFO for another 6 mths min., so 5-6 years before you can even apply, that is a long time to be breathing in this 5hit.
If you are young/single your lifestyle would be 100 times better with
VB/Jokestar/National Joke etc in Oz than it will be up here, IMHO. Most of those have staff travel and you wil enjoy seeing the world a lot more in your own time.
Good luck