Abstract. With the accumulation of data about biogenic volatile organic compounds (BVOCs) 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 Teflon-coated inner surface was characterized both in the lab with standard BVOC mixtures and in the field with typical broad-leaf and coniferous trees. The lab simulation with a constant flow of standard mixtures and online monitoring of BVOCs by proton transfer-time of flight-mass spectrometry (PTR-ToF-MS) revealed that lower real-time mixing ratios and shorter equilibrium times than theoretically predicted due to wall loss in the chamber, and larger flow rates (shorter residence times) can reduce the absorptive loss and improve the transfer efficiencies. However, even flow rates were raised to secure residence times 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 behavior. When the chamber was applied in the field to a branch of a mangifera indica tree, the enclosure-ambient 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 reducing equilibrium time, adsorptive loss and the ambient-enclosure temperature/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.

中文翻译：

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用于测量植物生物挥发性有机化合物 (BVOC) 排放的半开放式动态室的设计和表征

摘要。随着全球范围内基于分支规模围栏测量的植物生物挥发性有机化合物 (BVOC) 排放数据的积累，确保使用具有良好传输效率和对自然生长干扰较小的特性良好的动态室进行测量至关重要微环境。在这项研究中，在实验室中使用标准 BVOC 混合物和在典型阔叶树和针叶树的田间对自制的圆柱形半开放式动态室进行了表征，该室具有特氟龙涂层内表面。实验室模拟恒流标准混合物和通过飞行质谱的质子转移时间 (PTR-ToF-MS) 在线监测 BVOC 表明，由于壁的原因，实时混合比和平衡时间比理论预测的要低室中的损失，更大的流速（更短的停留时间）可以减少吸收损失并提高传输效率。然而，即使提高流速以确保停留时间小于 1 分钟，对于 α-蒎烯和 β-石竹烯等较重的 BVOC，转移效率仍低于 70%。与流速相比，相对湿度 (RH) 对 BVOC 的吸附损失的影响较小，化合物的特定模式与 RH 对其吸附行为的影响有关。当该室在现场应用于一个分支时 更大的流速（更短的停留时间）可以减少吸收损失并提高传输效率。然而，即使提高流速以确保停留时间小于 1 分钟，对于 α-蒎烯和 β-石竹烯等较重的 BVOC，转移效率仍低于 70%。与流速相比，相对湿度 (RH) 对 BVOC 的吸附损失的影响较小，化合物的特定模式与 RH 对其吸附行为的影响有关。当该室在现场应用于一个分支时 更大的流速（更短的停留时间）可以减少吸收损失并提高传输效率。然而，即使提高流速以确保停留时间小于 1 分钟，对于 α-蒎烯和 β-石竹烯等较重的 BVOC，转移效率仍低于 70%。与流速相比，相对湿度 (RH) 对 BVOC 的吸附损失的影响较小，化合物的特定模式与 RH 对其吸附行为的影响有关。当该室在现场应用于一个分支时 与流速相比，相对湿度 (RH) 对 BVOC 的吸附损失的影响较小，化合物的特定模式与 RH 对其吸附行为的影响有关。当该室在现场应用于一个分支时 与流速相比，相对湿度 (RH) 对 BVOC 的吸附损失的影响较小，化合物的特定模式与 RH 对其吸附行为的影响有关。当该室应用于现场的一个分支时mangifera indica树，随着流速从 3 L min ^-1（停留时间 ~ 4.5 分钟）至 15 L min ^-1（停留时间约 0.9 分钟）。在 9 L min ^-1的中等流速（停留时间约 1.5 分钟）下，对芒果和马尾松分支的动态室进行的现场测试显示，外壳温度在 +2 °C 和 CO ₂内升高与环境对应物相比，消耗在 -50 ppm 以内。结果表明，显着提高空气循环率将有利于减少平衡时间、吸附损失和环境外壳温度/RH 差异。然而，即使在更高的空气循环率和惰性 Teflon 涂层内表面下，单萜和倍半萜类物质的传输效率也不是那么令人满意，这意味着如果通过未经认证的传输的动态室获得这些物种的排放因子可能会被低估效率，并且需要进一步努力进行现场测量，以提高准确性并缩小排放因子的不确定性。