Air Purifiers.. what can you say about them?

I was wondering if anyone has experience with air purifiers.. I live in an apartment building and am expecting to have a baby soon. I am worried about dust from nearby construction sites, smells and smoke from neighbours’ balconies as well as odors that enter our home from the air conditioner..

Will purchasing be beneficial to me and my baby? What feautures should I look for when buying one? Any additional info will be very helpful..Thanks a lot..