@Lorna251 Sorry to hear about your situation. It looks like the "no smoking" rule is clearly stated in your listing as well as in your home. Every guest that books your accommodation is agreeing to these rules, and it is their responsibility to review the rules (whether they actually do or not). You have a couple options here.
1. You can give him a warning. Remind him that there is a strict no smoking rule and give him an opportunity to correct his behavior moving forward.
2. You can inform him that he has broken a rule he agreed to when booking, and you would like to end his reservation. If this is going to be your decision, I would first call Airbnb support, report the violation, then move forward with their assistance in cancelling the remainder of the reservation. This way you don't incur any penalties for cancelling. Just keep in mind, the guest might receive some funds back for the days in which he will not be staying.