If you want to improve your indoor air quality, you need to identify when it is bad. This will help you identify causes allowing you to either set up schedules for things like air purifiers or helping you change your behaviour in what causing poor indoor air quality.
The Dyson Pure Cool Air Purifying Fan has a built-in IAQ monitor itself, this is particularly useful as it allows the fan to be automated based on the air quality. It monitors more than average too, you get both PM2.5 and PM10, as well as VOC, NO2, temperature and humidity. The Dyson is also certified asthma & allergy friendly