First look at this conair portable air purifier you'll see that it's very small.  However, it's pretty powerful for its size. The battery lasts almost an entire day on the low setting (it's very quiet), the higher setting it last around 4 hours (kind of noisy, can double as a fan for feeling and sound).  Charges via USB so this is great to use at your desk.
I'd recomment purchasing this for smaller spaces or even if you're just looking for a portable fan.