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

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.

Phương pháp phân tích khí hồng ngoại buồng tĩnh kín và ứng dụng trong việc xác định lượng carbon phát thải qua hô hấp đất tại rừng ngập mặn Cần Giờ

Nghiên cứu hô hấp đất là một hướng nghiên cứu có đóng góp quan trọng vào việc đánh giá khả năng trao đổi và tích trữ Carbon (C) của hệ sinh thái rừng. Sự phát thải C của hệ sinh thái thông qua quá trình hô hấp của đất rừng có thể được xác định bằng nhiều phương pháp và thiết bị khác nhau, nhưng phổ biến nhất là phương pháp buồng tĩnh kín. Trong nghiên cứu này, hô hấp đất của hệ sinh thái tự nhiên rừng ngập mặn Cần Giờ (Thành phố Hồ Chí Minh) được đo bằng phương pháp buồng kín di động (DC-Dynamic chamber method) tại 12 sinh cảnh rừng tự nhiên với kích thước ô mẫu 20 m x 20 m. Thông lượng CO2 phát thải từ đất vào khí quyển thu được qua buồng kín được lưu chuyển đến thiết bị phân tích khí hồng ngoại IRGA xách tay và quay trở lại buồng phục vụ việc đánh giá các thông số đo đạc. Kết quả cho thấy rừng ngập mặn Cần Giờ phát thải C qua hô hấp đất với thông lượng trung bình 4,39 µmolCO2.m-².s-¹. Lượng CO2 phát thải qua đất thay đổi theo không gian, thời gian và có mối tương quan với nhiệt độ và độ ẩm buồng đo. Nhiệt độ và độ ẩm buồng đo cùng chế độ thủy triều có tác động đến sự phát thải CO2 qua hô hấp đất tại mỗi vị trí ô mẫu.

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

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.

Application of Dairy Manure Amended with Mineral Fertilizer on Stubble-Covered Soil: Effects on Ammonia Emissions

The reduction in the manure application rates through enrichment with mineral fertilizer has the potential to reduce costs, decrease environmental pollution, and extend the manure benefits to greater acreage. A pot experiment was carried out to assess ammonia emissions from dairy manure amended with mineral fertilizers applied on wheat stubble. The treatments were: control (no fertilization), urea (U), calcium ammonium nitrate (AN), dairy manure (MAN), urea + dairy manure (UMAN), and calcium ammonium nitrate + dairy manure (ANMAN). A dynamic chamber system was used to measure NH3 emissions during seven days after soil application. UMAN and ANMAN treatments led to higher NH3 emissions than each isolated component. This might be motivated by the manure pH. Thus, the enrichment of dairy manure with U or AN for application on stubble-covered soil should not be recommended. Nevertheless, some manure pre-treatments, such as acidification, or the use of other mineral fertilizers might improve such solution.

Key Role of Equilibrium HONO Concentration over the Soil

<p>Nitrous acid (HONO) is an important component of the nitrogen cycle. HONO can also be rapidly photolyzed by actinic radiation to form hydroxyl radicals (OH) and exerts a primary influence on the oxidative capacity of the atmosphere. The sources and sinks of HONO, however, are not fully understood. Soil nitrite, produced via nitrification or denitrification, is an important source for the atmospheric HONO production. [HONO]*, the equilibrium gas phase HONO concentration over the soil, has been suggested as key to understanding the environmental effects of soil fluxes of HONO (Su et al., 2011). But if and how [HONO]* may exist and vary remains an open question. In this project, a measurement method using a dynamic chamber has been developed to derive [HONO]* and the atmospheric soil fluxes of HONO can accordingly be quantified. We demonstrate the existence of [HONO]* and determine its variation in the course of soil drying processes. We show that when [HONO]* is higher than the atmospheric HONO concentration, HONO will be released from soil; otherwise, HONO will be deposited on soil. This work advances the understanding of soil HONO emissions, and the evaluation of its impact on the atmospheric oxidizing capacity and the nitrogen cycling.</p>

Mobile open dynamic chamber measurement of methane macroseeps in lakes

Methane (CH4) seepage; i.e., steady or episodic flow of gaseous hydrocarbons from subsurface reservoirs, has been identified as a significant source of atmospheric CH4. However, radiocarbon data from polar ice cores recently brought into question the magnitude of fossil CH4 seepage naturally occurring. In northern high latitudes, seepage of subsurface CH4 is impeded by permafrost and glaciers, which are under an increasing risk of thawing and melting in a globally warming world, implying the potential release of large stores of CH4 in the future. Resolution of these important questions requires a better constraint and monitoring of actual emissions from seepage areas. The measurement of these seeps is challenging, particularly in aquatic environments, because they involve large and irregular gas flowrates, unevenly distributed both spatially and temporally. Large macroseeps are particularly difficult to measure due to a lack of lightweight, inexpensive methods that can deployed in remote Arctic environments. Here, we report the use of a mobile chamber for measuring emissions at the surface of ice-free lakes subject to intense CH4 macroseepage. Tested in a remote Alaskan lake, the method was validated for the measurement of fossil CH4 emissions of up to 1.08 × 104 g CH4 m-2 d-1 (13.0 L m-2 min-1 of 83.4 % CH4 bubbles), which is within the range of global fossil methane seepage and several orders of magnitude above standard ecological emissions from lakes. In addition, this method allows for low diffusive flux measurements. Thus, the mobile chamber approach presented here covers the entire magnitude range of CH4 emissions currently identified, from those standardly observed in lakes to intense macroseeps, with a single apparatus of moderate cost.

CO2 mitigation strategies based on soil respiration

Soil, in addition to storing is a source of CO2 to the atmosphere emitted by soil respiration, mainly due to land use change. The objective of the research was to evaluate soil respiration in different uses and quantify its CO2 emissions at two different times of the year, as well as estimate the storage of this to make a balance to establish strategies that allows with the climate change mitigation. Using a closed dynamic chamber placed on the soil and integrated with an infrared gas analyzer measured the CO2 emission every 30 min, as well as temperature and moisture of the soil with sensors. Three land uses (agroforestry, forestry and agricultural) and two seasons of the year (summer and winter) were analyzed for 24 continuous hours at each site. Positive correlation between ambient temperature and soil respiration was found to exist. The agricultural system stores low carbon content in the soil (50.31 t C ha-1) and emits 9.28 t of C ha-1 in the highest temperature season, in contrast to a natural system that emits 3.98 t of C ha-1 and stores 198.90 t of C ha-1. The balance sheet reflects the need to know CO2 emissions to the atmosphere from soils and not just warehouses. Having scientific support from the ground to the atmosphere is an important step in decision-making that will contribute to climate change mitigation.