Fast response measurements of biogenic volatile organic compounds (VOC) using proton-transfer-reaction mass spectrometry (PTR-MS) were conducted above a deciduous temperate, a tropical rain and an evergreen needle forest.We explore howthe variance of a compound relates to the surface flux and lifetime (τ) at these sites. Our results suggest that a modified variance method can be used for estimating surface fluxes of isoprene and methanol above sites characterized by homogenous surface emissions. The normalized variability σC/C, generally used for variability–lifetime relationships, increases as a function of averaging period, and follows an inverse lifetime-dependence. The variability of short-lived compound lies within the predicted range for mixed layer parameterizations such as the top-down (TD)–bottom-up (BU) variance functions. For lifetimes >1 day, significant deviation due to mesoscale processes adds to the variability on timescales above \~{}30min.