I quit for 1 reason: I decided I wanted to quit. It wasn't healthy & my small children deserved better. I was ready, completely of my own decision. I made the decision that as much as I enjoyed smoking, I was going to live my life without ever doing it again. I just quit, cold turkey, right then & there. That was before the days of e-cigarettes. It was tough, real tough, but the decision was made & that was that.
Maybe instead of trying to convince him, you could try talking to him about it & ask him why he doesn't want to quit. Maybe, like I did, he really does enjoy smoking. Maybe he's in denial about what it's doing to him.
But in the end, it has to be his decision. When it is & it's time, let him know you'll be supportive.