Sniff your books as you dust them and separate those that have a musty or off-odor from those that have the natural smell of aging paper. Paper is made from wood and as the paper ages, it develops an aroma that some people find pleasant. Books that have been exposed to water or moisture in the air often develop the musty smell that can reduce the pleasure of reading or looking through the book.
Put the musty books in a paper or plastic bag to which kitty litter, baking soda or cornstarch has been added and seal them tight. The length of time that the books need to stay in the bag varies by the size of the book and the degree of off-odor emanating from the pages.
Check the smell of the books every few days. When the books smell fresh again, remove them and shake off the deodorizing products. You might do this outside if you used kitty litter, which could be messy in your kitchen sink or floor.