Why do old books smell so good? The answer is, as Science Switch reports, because they were made differently to modern ones, and are decaying.
An almond scent comes from benzaldehyde in the paper. Vanillin, the main compound in vanilla, is responsible for a sweet vanilla fragrance. Ethylbenzene, used in inks and paints, has a sweet plastic smell. 2-Ethyl hexanol, found in solvents and scents, smells lightly floral.
New books use modern chemicals like hydrogen peroxide and alkyl ketene dimers, so they give off different VOCs. The VOCs can also indicate exposure to smoke, water damage, or other aging factors.