Air Purifier

I kept thinking of buying an air purifier recently due to the haze (although it is better now). Anyone has any idea how to choose a suitable one? I tried to Google about it but I don't really understand the terminology. Confusing. Hope someone can recommend me a suitable brand and model and I will go and check it out! Preferably if you have used it before.

Many thanks. I have been turning on my air-con a lot last month and this month. Cannot imagine the utility bill.