a pleasing aroma
Why Old Books Smell Good
Lignin, the stuff that prevents all trees from adopting the weeping habit, is a polymer made up of units that are closely related to vanillin. When made into paper and stored for years, it breaks down and smells good. Which is how divine providence has arranged for secondhand bookstores to smell like good quality vanilla absolute, subliminally stoking a hunger for knowledge in all of us.
Source: Perfumes: the guide (Luca Turin and Tania Sanchez)
NEW books smell great, too!!