I think that is the ULTIMATE problem with HK people, everyone just say "buy a 空氣清新機, turn UP the air conditioning". The air conditioning is soooo cold in some places it's ridiculous.
It's a catch 22, bad air => more machines => cause more bad air.
this is purely cheating... when you open the can/bottle, the air will come out immediately, how can you take any of it? also, just one breath of fresh air can help your health in what way? anyone buy it is so silly...
oic... just "be-stupid"... don't know it until the end, haha...