Roxy, the IQs pretty much spew out clean air, but on a day in excess of 500,000PMs/litre, which is becoming commonplace in HKG between October and May, any purifier will struggle. I can't give exact figures but if it's +500,000 outside then your IQ will struggle to get that below the WHO limit of 60,000.
Of course, you and/or your family can't hide in your flat all day and very few places in HKG have air purifiers running and the ones I have seen are way too small for the area they are servicing and never cleaned.