Scent of knowledge: The molecular fingerprint of volatiles in an emblematic historical library in Italy

Heritage guidelines recognize odors as a value associated with a place. This study aims to clarify the connection between heritage and volatile organic compounds at the molecular level. At variance with previous studies, usually focused only on book-related compounds from accelerated degradation tests, the whole air of one of the most significant historical libraries in Italy was studied. A sampling of the volatiles off-gassing from the two most iconic rooms, respectively open and forbidden to visitors, was performed via a non-invasive, nondestructive green method, solid-phase-micro-extraction. The gas-chromatographic analyses resulted in the appraisal of olfactory contributions from books, storage environment, and, for the first time, anthropic activities and pollution.Concerning the paper decay process, for the very first time, the presence of 2-ethyl-1-hexanol in the chromatographic signature of the library air is rationalized according to the Guerbet reaction. The presence of all other compounds is explained by the paper decay process, anthropic sources, and pollution. Indoor air comprises analytes related to paper decay, identified by previous studies, and additional compounds never found before.Most volatile compounds are aliphatic and aromatic hydrocarbons, aldehydes, alcohols, terpenes, and terpenoids. Odor contributions from a selected number of analytes were pinpointed. Alkanes dominate the volatiles chromatographic signature, and impart a slight hydrocarbon smell. Aromatics supplement their characteristic aromatic odor. Aldehydes' very low odor threshold makes them strongly contribute to both fruity and fatty descriptors. Benzaldehyde, furfural, vanillin, and camphor add, respectively, an hint of almond, bread, vanilla, and camphor. Alcohols such as 2-ethyl hexanol have a floral scent. Wood-related terpenes and terpenoids contribute to the woody smell of the library.The digital molecular fingerprint of the "scent of knowledge" enables documentation, conservation, and future chemical reproduction of the historical library odor.