I believe that a person can only stop smoking when HE/SHE wants to stop!! Everyone I know who has stopped, stopped because they really wanted to; they decided to do it themselves!! I smoked thirty years and just quit one day because of my grandchildren...I wanted to know them and see them grow up. They are now in college and I am so thankful for being able to live this long and be friends with them!
Tell him all about the diseases and problems caused by smoking. Tell him that it can lead to lungs cancer if he doesn't give up. Try to tell him that you want him to leave smoking because you are really worried for his health. =) Best of luck.