I loaned out some books

I loaned a friend a couple of books. She brought them back, but they reek of cigarette smoke. I smoke, but these things now have a stench. I don't smoke in the house so my books aren't cooped us in a room while I do it. Does anyone know any ways to get the smell out? I tried a couple of things, but they either leave stains or don't work. I am thinking about letting them air out outside on the next dry day.