Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant N2O isotopocules

Nitrous oxide (N 2 O) is the primary atmospheric constituent involved in stratospheric ozone depletion and contributes strongly to changes in the climate system through a positive radiative forcing mechanism. The atmospheric abundance of N 2 O has increased from 270 ppb (parts per billion, 10 −9 mole mole −1 ) during the pre-industrial era to approx. 330 ppb in 2018. Even though it is well known that microbial processes in agricultural and natural soils are the major N 2 O source, the contribution of specific soil processes is still uncertain. The relative abundance of N 2 O isotopocules ( 14 N 14 N 16 N, 14 N 15 N 16 O, 15 N 14 N 16 O, and 14 N 14 N 18 O) carries process-specific information and thus can be used to trace production and consumption pathways. While isotope ratio mass spectroscopy (IRMS) was traditionally used for high-precision measurement of the isotopic composition of N 2 O, quantum cascade laser absorption spectroscopy (QCLAS) has been put forward as a complementary technique with the potential for on-site analysis. In recent years, pre-concentration combined with QCLAS has been presented as a technique to resolve subtle changes in ambient N 2 O isotopic composition.From the end of May until the beginning of August 2016, we investigated N 2 O emissions from an intensively managed grassland at the study site Fendt in southern Germany. In total, 612 measurements of ambient N 2 O were taken by com-bining pre-concentration with QCLAS analyses, yielding δ 15 N α , δ 15 N β , δ 18 O, and N 2 O concentration with a temporal resolution of approximately 1 h and precisions of 0.46 ‰, 0.36 ‰, 0.59 ‰, and 1.24 ppb, respectively. Soil δ 15 N-NO − 3 values and concentrations of NO − 3 and NH + 4 were measured to further constrain possible N 2 O-emitting source processes. Furthermore, the concentration footprint area of measured N 2 O was determined with a Lagrangian particle dispersion model (FLEXPART-COSMO) using local wind and turbulence observations. These simulations indicated that nighttime concentration observations were largely sensitive to local fluxes. While bacterial denitrification and nitrifier denitrification were identified as the primary N 2 O-emitting processes, N 2 O reduction to N 2 largely dictated the isotopic composition of measured N 2 O. Fungal denitrification and nitrification-derived N 2 O accounted for 34 %-42 % of total N 2 O emissions and had a clear effect on the measured isotopic source signatures. This study presents the suitability of on-site N 2 O isotopocule analysis for disentangling source and sink processes in situ and found that at the Fendt site bacterial denitrification or nitrifier denitrification is the major source for N 2 O, while N 2 O reduction acted as a major sink for soil-produced N 2 O.

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“…Data availability. Data are available at https://doi.org/10.17605/ OSF.IO/QPRJZ (Ibraim et al, 2019).…”

Section: Effect Of Manure Application On the Source Signaturesmentioning

confidence: 99%

Attribution of N2O sources in a grassland soil with laser spectroscopy based isotopocule analysis

et al. 2019

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“…The indicated numbers were chosen for the described experiments. b) The mini QC-TILDAS spectrometer is used in combination with a preconcentration device (Ibraim et al, 2018), the indicated N2O 5 concentration range is prior to preconcentration. c) The preconcentrationmini QC-TILDAS system is used in a repetitive batch cycle without a continuous sample gas flow (Ibraim et al, 2018(Ibraim et al, , 2019.…”

Section: Analytical Techniquesmentioning

confidence: 99%

“…A compact mini QCLAS device (CW-QC-TILDAS-76-CS; ARI, USA) coupled with a preconcentration system, called trace gas extractor (TREX) was provided by Empa, Switzerland. The spectrometer comprises a continuous-wave mid-infrared quantum cascade laser source emitting at 2203 cm -1 and an 15 astigmatic multipass absorption cell with a path length of 76 m and a volume of approximately 620 cm 3 (Ibraim et al, 2018) (Table 1). The TREX unit was designed and manufactured at Empa and is used to separate the N2O from the sample gas prior to QCLAS analysis.…”

Section: Trex-qclasmentioning

confidence: 99%

“…3.5.2 and 3.6.2, could be implemented by researchers when co-variation in both O2 and N2O in the sample gas is expected. Alternatively, as shown in this study, matrix and/or trace gas effects can be removed by automated N2O preconcentration devices such as TREX (Ibraim et al, 2018;Mohn et al, 2010), similar to IRMS. However, such devices are not commercially available, complex to build and 10 operate, and restrict sample frequency.…”

Section: Factors Affecting the Precision And Accuracy Of N2o Isotopocmentioning

confidence: 99%

“…CC BY 4.0 License. al., 2016;Rella et al, 2013;Vogel et al, 2013;Wen et al 2013), CH4 (Eyer et al, 2016;Griffith et al, 2012;Rella et al, 2013), and recently N2O isotope laser spectrometers (Erler et al, 2015;Harris et al, 2014;Ibraim et al, 2018;Wächter et al, 2008). However, a comprehensive and comparative characterization of the above effects for commercially-available N2O isotope analyzers is lacking.…”

Section: Introduction 20mentioning

confidence: 99%

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N2O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison

Harris¹,

Liisberg²,

Xia³

et al. 2019

Preprint

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Abstract. For the past two decades, the measurement of N2O isotopocules – isotopically substituted molecules 14N15N16O, 15N14N16O and 14N14N18O of the main isotopic species 14N14N16O – has been a promising technique for understanding N2O production and consumption pathways. The coupling of non-cryogenic and tuneable light sources with different detection schemes, such as direct absorption quantum cascade laser absorption spectroscopy (QCLAS), cavity ring-down spectroscopy (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS), 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. Here, we compared the performance of N2O isotope laser spectrometers with the three most common detection schemes: OA-ICOS (N2OIA-30e-EP, ABB-Los Gatos Research Inc.), CRDS (G5131-i, Picarro Inc.) and QCLAS (dual QCLAS and preconcentration (TREX)–mini QCLAS, Aerodyne Research Inc.). For each instrument, the precision, drift and repeatability of N2O mole fraction [N2O] and isotope data were tested. The analyzers 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 analyzer-specific correction functions. Subsequently, a simulated two end-member mixing experiment was used to compare the accuracy and repeatability of corrected and calibrated isotope measurements that could be acquired using the different laser spectrometers. Our results show that N2O isotope laser spectrometer performance is governed by an interplay between instrumental precision, drift, matrix effects and spectral interferences. To retrieve compatible and accurate results, it is necessary to include appropriate reference materials following the identical treatment (IT) principle during every measurement. Remaining differences between sample and reference gas compositions have to be corrected by applying analyzer-specific correction algorithms. These matrix and trace gas correction equations vary considerably according to N2O mole fraction, complicating the procedure further. Thus, researchers should strive to minimize differences in composition between sample and reference gases. In closing, we provide a calibration workflow to guide researchers in the operation of N2O isotope laser spectrometers in order to acquire accurate N2O isotope analyses. We anticipate that this workflow will assist in applications where matrix and trace gas compositions vary considerably (e.g. laboratory incubations, N2O liberated from wastewater or groundwater), as well as extending to future analyzer models and instruments focusing on isotopic species of other molecules.

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An approach for calibrating laser‐based N₂O isotopic analyzers for soil biogeochemistry research

Stuchiner

Weller

Fischer

2020

Rapid Comm Mass Spectrometry

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RationaleTechnological advances have motivated researchers to transition from traditional gas chromatography/isotope ratio mass spectrometry to rapid, high‐throughput, laser‐based instrumentation for N2O isotopic research. However, calibrating laser‐based instruments to yield accurate and precise isotope ratios has been an ongoing challenge. To streamline the N2O isotope research pipeline, we developed the calibration protocol for laser‐based analyzers described here. While our approach is targeted at laboratory soil incubations, we anticipate that it will be broadly applicable for diverse types of stable isotope research.MethodsWe prepared standards diluted from USGS52 and from a commercial cylinder to develop a calibration curve spanning from 0.3 to 300 ppm N2O. To calibrate over this broad range, we binned each isotopocule (N2O, N15NO, 15NNO, and NN18O) into low, medium, and high concentration ranges and then used mathematically similar polynomial functions to calibrate the isotopocules within each concentration range. We also assessed the temporal stability of the instrument and the capacity for our calibration approach to work with isotopically enriched gas samples.ResultsOur calibration approach yielded generally accurate and precise data when isotopocules were calibrated in concentration ranges, and the measurements appeared to be temporally stable. For all isotopocules at natural abundance, the residual percentage error was smallest in the medium N2O range. There was more noise in the corrected isotopomers and isotopologue at natural abundance in samples with the lowest and highest N2O concentrations. Corrected isotopomer results from isotopically enriched samples were very precise.ConclusionsDeveloping our calibration strategy involved learning several key lessons: (1) calibrate isotopocules in distinct concentration ranges, (2) use mathematically similar models to calibrate the isotopocules in each range, (3) calibrated N2O concentrations and δ values tend to be most accurate and precise in the medium N2O range, and (4) we encourage users to take advantage of isotopic enrichment to capitalize on laser‐based instrument strengths.

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Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant N₂O isotopocules

Cited by 17 publications

References 39 publications

Attribution of N<sub>2</sub>O sources in a grassland soil with laser spectroscopy based isotopocule analysis

Attribution of N<sub>2</sub>O sources in a grassland soil with laser spectroscopy based isotopocule analysis

N<sub>2</sub>O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison

An approach for calibrating laser‐based N₂O isotopic analyzers for soil biogeochemistry research

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Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant N2O isotopocules

Cited by 17 publications

References 39 publications

Attribution of N&lt;sub&gt;2&lt;/sub&gt;O sources in a grassland soil with laser spectroscopy based isotopocule analysis

Attribution of N&lt;sub&gt;2&lt;/sub&gt;O sources in a grassland soil with laser spectroscopy based isotopocule analysis

N&lt;sub&gt;2&lt;/sub&gt;O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison

An approach for calibrating laser‐based N2O isotopic analyzers for soil biogeochemistry research

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Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant N₂O isotopocules

Attribution of N<sub>2</sub>O sources in a grassland soil with laser spectroscopy based isotopocule analysis

Attribution of N<sub>2</sub>O sources in a grassland soil with laser spectroscopy based isotopocule analysis

N<sub>2</sub>O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison

An approach for calibrating laser‐based N₂O isotopic analyzers for soil biogeochemistry research