I'd start with the landlord. Ask him/her to try and correct the problem. It's possible that they will just tell you there is nothing they can do, but it is at least worth trying before you spend your time and money and energy on this.

Then, if the landlord won't do anything, look to see if you can find the air ducts and block them off. If they are already blocked, try caulking around the edges, maybe with an expanding caulk. Also, try caulking around your plumbing--you want to seal off any place where air from their unit could be entering your unit.

Yea, me too. Complaint it to the landlords. They will take care of this.I am sure they will help you out.

In worst case try filters to abstain any harmful effects.

The landlords wont help if they are smokers like mine is, my biggest smell comes from down stairs into my food pantry, so what I did was put a small bowl of white vinegar in the pantry and it really has cut down on the stench of smoke. I also put a towel down so that the stench doesnt come out from under the door, HOPE that helps a little. Good Luck !!!