There are multiple ways of dealing with it:
1) I agree with KASDEGA, that is what exactly what my dad with me and he told me whenever I decide to quit ask him for help. It didn't made me quit smoking immediately, but it made me feel that how disappointed he was.
2) My mother on the other side tried to educate me by asking "Have you calculated what is this habit costing me in terms of money?" While I was not money conscious when I was a teenager, but a couple of years later, I realised that the habit was affecting my productivity with my studies. After smoking for 6 years I quit smoking for good. If he is hardworking then educate him how it affects productivity.
3) If he is scared of poor health, take him to place they educate on consequences of smoking.
4) If he is money conscious then educate him about how it is affecting or will affect his pockets.
5) If he is a sports person, educate him how this habit eats up his stamina.
My parents always expressed their concern about my smoking, sometimes I rebelled because it annoyed me but one day I realised that I should quit.It is been 15 years I quit but I still remember their role in educating me.
This is not only going to bother you but it will a big challenge for your son to quit smoking too. So be patient and show empathy. From my experience, patience and support you provide to your dependent son will be the key.