Neighbor won’t stop smoking in the house!!

So I live on top of the two apartments down stairs, it’s a weird set up but pretty much my house is on top of both of the people down stairs. Anyways, I have a 1 year old baby girl & this guy WONT STOP SMOKING IN THE HOUSE... KNOWING IT GOES STARIGHT UP TO MY DAUGHTERS ROOM. I just walked in and it smells like I could’ve lit up a cigarette & smoked it In there. It’s just so fucking ignorant! Not only that but he’s like 34 with two kids in his house...!! The only problem is he’s very aggressive & very argumentative and I don’t wanna create problems with him and my bf.. any advice?