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. With the accumulation of data about biogenic volatile organic compound(BVOC) emissions from plants based on branch-scale enclosure measurementsworldwide, it is vital to assure that measurements are conducted usingwell-characterized dynamic chambers with good transfer efficiencies and less disturbance on natural growing microenvironments. In this study, a self-made cylindrical semi-open dynamic chamber with a Teflon-coated inner surface was characterized both in the lab with standard BVOC mixtures and in the field with typical broadleaf and coniferous trees. The lab simulation with aconstant flow of standard mixtures and online monitoring of BVOCs by protontransfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) revealedlower real-time mixing ratios and shorter equilibrium times thantheoretically predicted due to wall loss in the chamber and that larger flowrates (shorter residence times) can reduce the adsorptive loss and improvethe transfer efficiencies. However, even when flow rates were raised to secureresidence times of less than 1 min, transfer efficiencies were still below 70 % for heavier BVOCs like α-pinene and β-caryophyllene.Relative humidity (RH) impacted the adsorptive loss of BVOCs lesssignificantly when compared to flow rates, with compound-specific patternsrelated to the influence of RH on their adsorption behaviour. When thechamber was applied in the field to a branch of a Mangifera indica tree, the ambient–enclosure temperature differences decreased from 4.5±0.3 to 1.0±0.2 ∘C and the RH differences decreased from9.8 ± 0.5 % to 1.2±0.1 % as flow rates increased from 3 L min−1 (residence time ∼4.5 min) to 15 L min−1(residence time ∼0.9 min). At a medium flow rate of 9 L min−1 (residence time ∼1.5 min), field tests with thedynamic chamber for Mangifera indica and Pinus massoniana branches revealed enclosure temperature increasewithin +2 ∘C and CO2 depletion within −50 ppm whencompared to their ambient counterparts. The results suggested thatsubstantially higher air circulating rates would benefit by reducingequilibrium time, adsorptive loss, and the ambient–enclosure temperature and RHdifferences. However, even under higher air circulating rates and with inertTeflon-coated inner surfaces, the transfer efficiencies for monoterpene andsesquiterpene species are not so satisfactory, implying that emissionfactors for these species might be underestimated if they are obtained bydynamic chambers without certified transfer efficiencies and that furtherefforts are needed for field measurements to improve accuracies and narrowthe uncertainties of the emission factors.

Design and characterization of a semi-open dynamic chamber for measuring biogenic volatile organic compound (BVOC) emissions from plants