I have a very "comforting" story:
My grandma owns a cottage along a river in NW Pennsylvania. Well one day, I went out in the river on a kayak to an island. With my grandparents and brother (I'm not that old).
Well, once we got over there, after maybe a half hour or so, a five-year-old and his mom came to the island. We stayed there for a little bit then the boy (the five year old) invited us to his "cottage" (so to speak, it was more of a log cabin). And his dad was there, along with who I assume were the boy's aunt and uncle. The dad, was a very heavy smoker, not quite a chain smoker, but close. He was probably lighting up a cigarette every 15 minutes. The next day the same thing happened. However, the dad came over later and we didn't go over to the cabin. And on the island, which I think we stayed for maybe an hour and fifteen minutes, the dad smoked maybe 4 or 5 cigs. In an hour and fifteen minutes, give or take. And he was not setting a very good role model for his child.
So, you can obviously see some connection. My "story" was just to give another example.
And, my tip to you is show him the dangers of smoking online so he actually understands that he is killing himself. Furthermore, give him all his options to quit his habit for good. I hope it works.