I read through the posting and didn't find anyone who suggested moving south from HK island, Kowloon and the NT to an outer island such as Lamma. Many people simply would rather leave HK than to live 30 minutes by ferry or their own boat from Central than to be inconvenienced. Yes, there are few amenities on Lamma, but if one is truly seeking cleaner air head south away from autos, trucks, planes. Granted, the ferries are still using bunker as fuel but that will be eventually phased out. There are many families that realize that picking up groceries on Sunday either on their own or with a helper' s assistance is far easier than sitting inside with an air purifier. Yes, there are beaches nearby and residents do have washers, dryers, ovens and amazing views.
I also have a particular counter and 2 air purifiers at home and the number is about the same as yours (10% of the reading if i have windows opened). I don't have any lung or breathing issues (yet!) but i just want to spend close to 50% of my time breathing better quality air.
Dylos DC1100 Professional Air Quality Monitor (can get one from taobao)
Watch documentary on China Air Under the Dome by Chai Jing on youtube
No, actually not. It is proven cleaner and clearer both anecdotally and statistically.