Stability of monoterpenes in air at nominal 2 nmol mol–1. Contained in an Al-Experis cylinder. Measurements were made over a period of about 800 days from the date of preparation. The solid black line represents the first ratio determined for a monoterpene to the internal standard (n-hexane), with the corresponding dotted lines marking the k = 2 expanded uncertainty. Error bars for each ratio represent k = 2 expanded uncertainties. DOI: https://doi.org/10.1525/elementa.366.f6