I really need to know what the best air purifier for the elimination of cigarette smoke is. My dad smokes in his office which is RIGHT beside my bedroom.. he smokes gross native cigarettes in there ALL day long and refuses to smoke outside. He has blocked off the vents from his office to my room and has a fan that draws the smoke out of his office and out the window. I have an air purifier now and absolutely NOTHING works. It is so potent and it makes me sick. What is the best air purifier for this situation? price range $200-$500.. THANKS!