How can I get my dad to TRY to quit smoking?

He always smokes in the house and it’s making me sick. Whenever somebody tells him to go outside, he goes "ugh" and ignores us! The only place in the house that doesn’t smell like smoke is the very BACK room. The worst part is, he smokes at his computer desk and the desk is right around the kitchen! HELP! IS there any free thing to help him quit smoking? Thanks!