- 1Section of Organic Farming and Cropping Systems, University of Kassel, Witzenhausen, Germany
- 2Section of Ecological Plant Protection, University of Kassel, Witzenhausen, Germany
- 3Department of Applied Ecology, Hochschule Geisenheim University, Geisenheim, Germany
- 4Institute for Plant Ecology, Giessen University, Gießen, Germany
Closed chamber measurements are still the most common approach for measuring the exchange of greenhouse gases (GHG) between soils and the atmosphere in terrestrial ecosystems. Closed chambers can either be employed as static (discrete gas sampling with syringes and subsequent gas chromatographic analysis) or as dynamic chambers (in-field connection to a portable gas analyzer for real-time gas concentration measurements). Two well-known advantages of real-time continuous gas measurements at high frequencies (seconds to Hertz) are the reduction of chamber closure periods as well as the substantially lower minimum detectable flux (MDF). During the past two decades, the technological development of portable fast response analyzers has seen tremendous leaps and new manufacturers are emerging on the scene. In our pilot study, we compared the performance of two new mid-infrared absorption spectroscopy analyzers (a MIRA Ultra N2O/CO2 and a MIRA Ultra Mobile LDS: CH4/C2H6 analyzer, Aeris Technologies, USA) with the performance of a gas chromatograph (Bruker Model 450, Bruker Corp., USA) for the quantification of CO2, CH4, and N2O fluxes under field conditions in a cropland. For the closed chamber measurements, both analyzers were connected to a single chamber, running in parallel, while simultaneously discrete gas samples were taken with a syringe at six discrete time points throughout the chamber closure times for the subsequent gas chromatographic analysis. Measurements took place at two separate days covering lower and higher soil gas fluxes. Regarding CO₂ fluxes, the results demonstrated a strong agreement between the methods, with minimal deviations for both higher and relatively smaller fluxes (normalized root mean square error, nRMSE < 12.5%). A high level of agreement between the methods was also observed for N₂O fluxes on the first measurement day, when a N₂O pulse occurred (nRMSE < 9.5 %). However, on the second measurement day, the agreement was considerably lower for very small negative fluxes. For CH₄, the agreement between methods was very low (nRMSE < 213.6%). Due to the higher analytical precision of the MIRAs, the MDFs for the closed dynamic chamber measurements were considerably lower compared to the closed static chamber measurements. This enabled the detection of significant fluxes even at very low flux rates which could not be distinguished from the background measurement noise of the closed static chamber method using GC analysis. The discrepancies between the two approaches were foremost restricted to fluxes which were below the closed static chamber MDFs. The presented results will support an informed selection of suitable gas analytical methods for measuring GHG fluxes in the field and help the soil flux research community to keep up with the rapidly developing market of portable fast-response analyzers.
(Wolfgang Aumer and Morten Möller contributed equally to this study and abstract and are considered co-first authors.)
How to cite: Möller, M., Aumer, W., Eckhardt, C., Görres, C.-M., Bruns, C., and Kammann, C.: Comparison of miniature mid-infrared absorption spectroscopy analyzers with gas chromatography for the quantification of soil greenhouse gas fluxes using the closed chamber method, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18698, https://doi.org/10.5194/egusphere-egu25-18698, 2025.
