Even if you are not technically getting what most other folk would deem "high" from this continual invasion of secondhand smoke, Joe, you have a highly (lol! ) valid complaint!

Some folk, who are very sensitive to tobacco or weed smoke -- including some previous smokers of same, in fact -- have true difficulties coping w/it.

Section 8 frowns on situations such as the one you're experiencing, in my longish experience. Unless MJ is legal where you live, which is unlikely but not impossible -- then he could get in deep sewage with the Housing Authority ! Not that I think you should threaten him with that, but it's a card to keep in one's back pocket if all else fails.

Please have a good intensive read of your lease terms. It probably contains provisions for "Lawful Use" and possibly terms involving "The peaceful enjoyment of my home" or similar wording. It is landlord's responsibility to assure that -- and he isn't, imo. In fact, he's interfering.

An Air Purifier with a good strong filter sounds a great and reasonable idea in the interim between now and going into a different flat when/if available. Very best of luck; sorry your home is being infringed upon by this inconsiderate jerk.

Chyia, in full sympathy (pot smoke tends to trigger headaches for me, and fiancé is on medical MJ-- whee. lol)