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Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas N2O. Despite their importance, shifts in terrestrial N loss pathways driven by global change are highly uncertain. Here we present a coupled soil-atmosphere isotope model (IsoTONE) to quantify terrestrial N losses and N2O emission factors from 1850-2020. We find that N inputs from atmospheric deposition caused 51% of anthropogenic N2O emissions from soils in 2020. The mean effective global emission factor for N2O was 4.3 ± 0.3% in 2020 (weighted by N inputs), much higher than the surface area-weighted mean (1.1 ± 0.1%). Climate change and spatial redistribution of fertilisation N inputs have driven an increase in global emission factor over the past century, which accounts for 18% of the anthropogenic soil flux in 2020. Predicted increases in fertilisation in emerging economies will accelerate N2O-driven climate warming in coming decades, unless targeted mitigation measures are introduced.

Methods and techniques are described for automated measurements of greenhouse gases (GHGs) in both the laboratory and the field. Robotic systems are currently available to measure the entire range of gases evolved from soils including dinitrogen (N2). These systems usually work on an exchange of the atmospheric N2 with helium (He) so that N2 fluxes can be determined. Laboratory systems are often used in microbiology to determine kinetic response reactions via the dynamics of all gaseous N species such as nitric oxide (NO), nitrous oxide (N2O), and N2. Latest He incubation techniques also take plants into account, in order to study the effect of plant-soil interactions on GHGs and N2 production. The advantage of automated in-field techniques is that GHG emission rates can be determined at a high temporal resolution. This allows, for instance, to determine diurnal response reactions (e.g. with temperature) and GHG dynamics over longer time periods.

Several approaches exist for measuring greenhouse gases (GHGs), mainly CO2, N2O, and CH4, from soil surfaces. The principle methods that are used to measure GHG from agricultural sites are chamber-based techniques. Both open and closed chamber techniques are in use ; however, the majority of field applications use closed chambers. The advantages and disadvantages of different chamber techniques and the principal steps of operation are described. An important part of determining the quality of the flux measurements is the storage and the transportation of the gas samples from the field to the laboratory where the analyses are carried out. Traditionally, analyses of GHGs are carried out via gas chromatographs (GCs). In recent years, optical analysers are becoming increasingly available ; these are user-friendly machines and they provide a cost-effective alternative to GCs. Another technique which is still under development, but provides a potentially superior method, is Raman spectroscopy. Not only the GHGs, but also N2, can potentially be analysed if the precision of these techniques is increased in future development. An important part of this chapter deals with the analyses of the gas concentrations, the calculation of fluxes, and the required safety measures. Since non-upland agricultural lands (i.e. flooded paddy soils) are steadily increasing, a section is devoted to the specificities of GHG measurements in these ecosystems. Specialised techniques are also required for GHG measurements in aquatic systems (i.e. rivers), which are often affected by the transfer of nutrients from agricultural fields and therefore are an important indirect source of emission of GHGs. A simple, robust, and more precise method of ammonia (NH3) emission measurement is also described.

The latest commercial laser spectrometers have the potential to revolutionise nitrous oxide (N2O) isotope analysis: they provide continuous and rapid analysis, measure at ambient concentrations without pre-concentration, and are field-deployable. However, to do so, they must be able to produce trustworthy data.Here, we present results from a series of experiments performed on N2O isotope laser spectrometers with different detection schemes: off-axis integrated cavity output spectroscopy (OA-ICOS, ABB-Los Gatos Research Inc.), cavity ring-down spectroscopy (CRDS, Picarro Inc.) and direct absorption quantum cascade laser absorption spectroscopy (QCLAS, Aerodyne Research Inc.). For each instrument, the precision, drift and repeatability of N2O mole fraction [N2O] and isotope data were tested. The analysers were then characterized for their dependence on [N2O], gas matrix composition (O2, Ar) and spectral interferences caused by H2O, CO2, CH4 and CO to develop analyser-specific correction functions. Based on these results, we developed a calibration workflow which allows for reproducible and accurate data to be generated using these instruments. We assessed the robustness of this workflow by measuring a series of gas mixtures of known N2O isotopic composition, but with varying N2O and other trace gas concentrations, to compare the accuracy and repeatability of calibrated measurements obtained by the different analysers. We show that, provided the compositional differences between reference gases and samples gases can be accounted for (either by implementing chemical traps or interference correction functions), reproducible and accurate data can be obtained.Our results also clearly highlight that N2O isotope laser spectrometers are not “plug and play” devices, and that N2O isotope analysis using laser spectroscopy is not straight-forward. Instead, researchers wishing to use these instruments need to carefully consider the desired application, precision and accuracy, and

Measurements of the four most abundant stable isotopocules of N2O (14N14N16O, 15N14N16O, 14N15N16O, and 14N14N18O) can provide a valuable constraint on source attribution of atmospheric N2O. N2O isotopocules at natural abundance levels can be analyzed by isotope-ratio mass-spectrometry (IRMS) [1] and more recently optical isotope ratio spectroscopy (OIRS) [2]. OIRS instruments can analyze the N2O isotopic composition in gaseous mixtures in a continuous-flow mode, providing real-time data with minimal or no sample pretreatment, which is highly attractive to better resolve the temporal complexity of N2O production and consumption processes. Most importantly, OIRS laser spectroscopy is selective for position-specific 15N substitution due to the existence of characteristic rotational-vibrational spectra.By allowing both in-situ application and measurements in high temporal resolution, laser spectroscopy has established a new quality of data for research on N2O in particular and N cycling in general. However, applications remain challenging and are still scarce as a metrological characterization of OIRS analyzers, reporting factors limiting their performance is still missing. In addition, only since recently two pure N2O isotopocule reference materials have been made available through the United States Geological Survey (USGS), which however, only offer a small range of δ15N and δ18O values (< 1 ‰) and are therefore not suited for a two-point calibration approach [3].This presentation will highlight the recent progress achieved within the framework of the EMPIR project “Metrology for Stable Isotope Reference Standards (SIRS)”, namely:(1) The development of pure and diluted N2O reference materials (RMs), covering the range of isotope values required by the scientific community. These gaseous standards are available as pure N2O or N2O diluted in whole air. N2O RMs were analyzed by an international group of laboratories for δ15N, δ18O (MPI-BGC, Tokyo Institute of Technology

Over the last two decades, research involving N2O isotopic analysis has been stimulated by continuing analytical progress in isotope-ratio mass-spectrometry (IRMS) and more recently by the development of mid-infrared laser spectroscopy. The advancement of laser spectroscopic techniques was enabled by the invention and availability of quantum cascade lasers (QCL), which have been coupled with different detection schemes such as direct absorption quantum cascade laser absorption (QCLAS), cavity ring down (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS) to realize compact field-deployable analyzers. To improve the accuracy and reliability of these instrumental techniques, analyzer-specific calibration procedures and correction algorithms are required to account for matrix effects, spectral interferences and drift during measurements. We performed an inter-comparison study of three commercially-available N2O isotope laser spectrometers (δ15Nα, δ15Nβ & δ18O); Aerodyne Research (dual QCLAS, with/without pre-concentration, Picarro (G5131-i) and Los Gatos Research (Model 914-0027). Gas matrix effects were investigated by determining the dependence of N2O isotope deltas on the analysis in an “ambient” N2/O2/Ar/CO2/CH4/CO versus a simplified N2/O2/Ar or N2/O2 matrix. In addition, spectral interferences of enhanced trace gas concentrations (CO2, CH4, CO, H2O) were characterized and strategies for removal tested. Short-term and long-term repeatability, drift and dependence of isotope deltas on N2O concentrations were also quantified and compared among instruments. Using these results, we evaluated the accuracy of individual analyzers and developed calibration strategies tailored to each machine. Our study will guide the selection of instruments for specific applications (e.g. ambient air versus chamber measurements), and foster the development of N2O isotope reference gases optimized for laser spectrometers currently ongoing within the EMPIR project “Metrolog

For the past two decades, N2O isotopocules – isotopically substituted molecules 14N15N16O, 15N14N16O and 14N14N18O of the main isotopic species 14N14N16O – have been identified as promising tools for understanding N2O production and consumption pathways. The application of midinfrared laser spectroscopy to the study of N2O isotopocules continues to grow due to recent progress in analyzer development. The coupling of non‐cryogenic and tuneable light sources with differentdetection schemes, such as direct absorption quantum cascade laser spectroscopy (QCLAS), cavity ring‐down spectroscopy (CRDS) and off‐axis integrated cavity output spectroscopy (OAICOS), has enabled the production of commercially‐available and field‐deployable N2O isotopic analyzers.In contrast to traditional isotope‐ratio mass‐spectrometry (IRMS), these instruments are inherently selective for position‐specific 15N substitution and provide real‐time data, with minimal or no sample pretreatment, which is highly attractive for process studies.In this workshop, we will present the results of an intercomparison study that we conducted on various N2O isotope laser spectrometers that use the three most common detection schemes: OAICOS (N2OIA‐30e‐EP, ABB‐Los Gatos Research Inc.), CRDS (G5131‐i, Picarro Inc.) and QCLAS (dual QCLAS, preconcentration – mini QCLAS, Aerodyne Research Inc.). Analyzers were tested for their concentration dependence, and gas matrix (N2, O2, Ar) and trace gas (H2O, CO2, CH4, CO) interference effects to compare the magnitude of these effects across instruments, and to develop analyzer‐specific correction functions. The instruments were also characterized for precision, repeatability and instrumental, and the accuracy of corrected results standardized to international scales were compared among laser spectrometers and to IRMS in a simulated two end‐member mixingexperiment.We will show that N2O isotope laser spectrometer performance is governed by a complex interplay between instrumen

Over the last two decades, research involving N2O site specific isotopic analysis has been stimulated by continuing analytical progress in isotope-ratio mass-spectrometry (IRMS) and more recently mid-infrared laser spectroscopy. This development has been triggered by the invention and availability of quantum cascade lasers (QCL), which offer high optical power in continuous wave operation at room temperature. QCL light sources have been combined with different detection schemes such as direct absorption (QCLAS), cavity ring down (CRDS) and off-axis integrated cavity output (OA-ICOS) to realize compact, field-deployable analyzers.The availability of temporal resolved N2O isotopic information in real-time will deepen our process-level understanding of the nitrogen cycle. It will also open up entirely new research areas that will attract an increasing number of application-oriented scientists. Provided that the novel laser spectrometers produce compatible and thus accurate results (i.e. traceable to the international isotope ratio scales, AIR-N2 for 15N/14N and VSMOW for 18O/16O), the implementation of these instruments will lead to a further dissemination of N2O isotopic research.We will present results of an inter-comparison study on the three most common commercial N2O isotope analyzers, including Aerodyne Research (dual QCLAS, with/without TREX), Picarro (G5131-i) and Los Gatos Research (Model 914-0027). Most importantly, gas matrix effects were investigated by determining the dependence of N2O isotope deltas on the analysis in an “ambient” N2/O2/Ar/CO2/CH4/CO versus a simplified N2/O2/Ar or N2/O2 matrix. In addition, spectral interferences of enhanced trace gas concentrations (CO2, CH4, CO, H2O) were characterized and strategies for removal tested. Short-term and long-term repeatability, drift and dependence of isotope deltas on N2O concentrations were also quantified and compared among instruments. Based on these results a calibration strategy was established and