In bought a Honeywell HEPA purifier at the beginning of winter, got it from Taobao. They call it a desk top model, but it's actually the size of a ghetto blaster so works best stuck on a table you're not using. I smoke and I live with a dog, it's a small flat, three main rooms.
I would turn it on when I left for class and when I came home after class my flat smelt fresh, and my dog's asthma/ tracheal collapse choking issues cleared up within a day or two of buying it. I reckon it works.
I paid just on 500rmb, for the unit and the power transformer that came with it, it's US made so needed a transformer.
Smalk enough to carry from room to room, where the pollutants are and big enough to be effective.
Aside from my goose down quilt, it was my best purchase for all of last year.
R and The Dog xx