Why do old books smell so good?

The smell of the old books is mainly because of paper and inks. Paper is mainly made up of wood. Wood is primarily made up of cellulose and lignin. Over the years, these compounds react with moisture, air and heat and begin to release Volatile Organic Compounds(VOCs). These compounds easily vaporize and mix in the air and thus forming the smell of old books.There are different type of VOCs. A Volatile Organic Compound called Vanillin gives vanilla like smell. Benzaldehyde gives almond like smell. Ethyl benzene gives a sweet smell. The combination of these various compounds makes books smell so good.