That would be a HUGE problem for me with two asthmatics who are triggered by secondhand smoke. What are the laws in your state regarding smoking in apartments/common areas/restaurants/etc? Also, you sound like you are in a complex. Does your management company have laws regarding smoking? Are the units rented as "no smoking?" I would contact management and let them sort it out. You likely have air flow vents between the units and management will have to rectify the situation with the tentants who are smoking in the unit or you'll have to ask to be moved to another unit. It's near impossible to get rid of smoke coming through vents. If it was a stale smoke odor from before it would be tough but it would be something you could deal with. But an ongoing smoke issue isn't going to be fixed with air purifiers.
It depends where the smoky air is coming in. In some places I've lived, it has helped a lot to tape around the openings in the walls where pipes come through, and to put weatherstripping around the door. With fans, make sure that they are pulling clean air into your apartment.
i am super sensitive to smoke. i can smell even a tiny bit of it.
sadly the only thing that has worked is to move. and live in a smoke free apt. complex.
i have tried many many things. but cigarette smoke is very insidious. even if i am standing next to a smoker who had smoke on their clothes but werent smoking around me, i'd come home smelling as if i have been smoking.
sorry. i know that's not very helpful. but really i have never ever succeeded with any measures i have taken. esp. if you live above a smoker.