**2.1 Chemicals and reagents**

A pure reference compounds including heptanal, benzaldehyde, octanal, *(E)*- 2-octenal, decanal, dodecanal, all *n*-hydrocarbons, butyl butyrate, 6-methyl-5 hepten-2-one, naphthalene, acetophenone, phenol, β-pinene, *p*-cymene, limonene, γ-terpinene, 1,8-cineole, α-terpineol, verbenone, bornyl acetate, longifolene, geranylacetone (*E + Z* isomers), 1-octanol, 1-decanol, ethyl benzoate, 2-undecanone, α-thujone + β-thujone mixture, and pulegone were purchased from Sigma, Aldrich, Supelco and Merck and used to compare retention times and mass spectra.
