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

Abstract

Abstract. With the accumulation of data about biogenic volatile organic compound (BVOC) emissions from plants based on branch-scale enclosure measurements worldwide, it is vital to assure that measurements are conducted using well-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 a constant flow of standard mixtures and online monitoring of BVOCs by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) revealed lower real-time mixing ratios and shorter equilibrium times than theoretically predicted due to wall loss in the chamber and that larger flow rates (shorter residence times) can reduce the adsorptive loss and improve the transfer efficiencies. However, even when flow rates were raised to secure residence 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 less significantly when compared to flow rates, with compound-specific patterns related to the influence of RH on their adsorption behaviour. When the chamber 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 from 9.8 ± 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 the dynamic chamber for Mangifera indica and Pinus massoniana branches revealed enclosure temperature increase within +2 ∘C and CO2 depletion within −50 ppm when compared to their ambient counterparts. The results suggested that substantially higher air circulating rates would benefit by reducing equilibrium time, adsorptive loss, and the ambient–enclosure temperature and RH differences. However, even under higher air circulating rates and with inert Teflon-coated inner surfaces, the transfer efficiencies for monoterpene and sesquiterpene species are not so satisfactory, implying that emission factors for these species might be underestimated if they are obtained by dynamic chambers without certified transfer efficiencies and that further efforts are needed for field measurements to improve accuracies and narrow the uncertainties of the emission factors.

Emissions of isoprenoids from dominant tree species in subtropical China

“…Branch-level BVOC emissions were measured by a cylindrical semi-open dynamic chamber, which is made of polymethyl methacrylate with an inner surface coated with fluorinated ethylene propylene (FEP) Teflon film (FEP 100, Type 200A, DuPont, Witton, USA). Detailed information about the design and characterization of this dynamic chamber was described in our previous study (Zeng et al, 2022). Briefly, the chamber has a volume of 13.7 L with a diameter of 250 mm and a height of 280 mm, the flow of circulating air is maintained at a rate of 9 L min −1 by a mass flow controller (Alicat Scientific, Inc., Tucson, AZ, USA) connected to an air pump (MPU2134-N920-2.08, KNF, Freiburg, Germany).…”

“…Then, the chamber was initially flushed with ambient air for 1-2 h to avoid erratic emissions caused by artificial disturbance on the physiological state of the enclosed leaves and to ensure that the emissions in the chamber were stable (Niinemets et al, 2011). Subsequently, the chamber air flowed through an ozone scrubber (Na 2 S 2 O 3 , Helmig et al, 2007;Zeng et al, 2022), followed by an automatic sampler (JEC921, Jectec Science and Technology, Co., Ltd., Beijing, China) equipped with adsorbent cartridges with a constant flow rate of 200 mL min −1 , and the emitted BVOCs were retained in commercial adsorbent cartridges bedded with Tenax TA (35/60 mesh, 150 mg) and Carbograph 5TD (35/60 mesh, 150 mg) (C2-AAXX-5149, Markes International Ltd., Bridgend, UK) for 10 min. Ambient air near the inlet was collected concurrently in the same way with another automatic sampler to determine the background concentration.…”

“…The reported emission rates for isoprene and total MTs varied by up to several orders of magnitude. The reliability of static enclosure measurements is questionable in comparison with dynamic enclosure measurements (Niinemets et al, 2011;Li et al, 2019;Zeng et al, 2022). The laboratory control measurements for seedlings (Tsui et al, 2009;Leung et al, 2010), however, may not well-represent real-world emissions from mature trees under natural growing environments (Niinemets et al, 2011;Emmerson et al, 2016).…”

“…However, there are large uncertainties in both the amounts and the compositions of BVOC emissions (Klinger et al, 2002;Li et al, 2020;Ma et al, 2021). Unlike previous studies in this region that mostly involved static enclosures with seedlings in the laboratory to measure emissions of isoprene and total MTs, the present study aims: (1) to obtain real-world emission factors of isoprenoids for dominant tropical/subtropical tree species under natural growing environments by applying a dynamic chamber that was systematically evaluated (Zeng et al, 2022); (2) to quantify the emission rates of individual MTs and SQTs along with isoprene; and (3) to provide the localized emission factors that can be used to update BVOC emission estimates in the region.…”

An Overview of the Isoprenoid Emissions From Tropical Plant Species

“…Enclosed measurement systems, initially developed by Zimmerman (1979) , are the most commonly used sampling method for studying BVOCs from tropical plants ( Guenther et al, 1996a Greenberg et al, 2003 ; Harley et al, 2003 , 2004 ; Padhy and Varshney, 2005a ; Tambunan et al, 2006 ; Singh et al, 2008 , 2011 ; Niinemets et al, 2011 ; Malik et al, 2018 , 2019 ; Zeng et al, 2022 ). Enclosure, however, may underestimate emissions due to foliar shading ( Guenther et al, 1996a ) and contribute erratic emissions to α-pinene ( Padhy and Varshney, 2005b ).…”