Neighbor who smokes

We have a next-door neighbor who is a heavy smoker, as are his visitors, it seems. The smoke is seeping into the bedroom that adjoins his apartment. I've done everything I can to seal off that space (even putting little things into the outlet holes, because I heard smoke can seep in there) but it's still really smoky. I have an air purifier going all the time, but the room still stinks. I'm considering offering to give him an air purifier, which would be small and quiet but might help. Is that obnoxious? He seems like a nice guy, but is pretty private and quiet.