Continuous measurements of nitrous oxide isotopomers during incubation experiments

Winther, Malte; Balslev-Harder, David; Christensen, Søren; Priemé, Anders; Elberling, Bo; Crosson, E.; Blunier, Thomas

doi:10.5194/bg-15-767-2018

Cited by 37 publications

(21 citation statements)

References 46 publications

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“…Until recently, the main disadvantages of CRDS instruments have been the relatively large sample size requirement (20-130 nmol-N 2 O) and the lack of automatic sample preparation. To this end, researchers who attempted to utilize laser-based N 2 O systems for aquatic nitrogen and oxygen isotopic analyses were limited to (1) extraction of dissolved N 2 O using a gas equilibration device under continuousflow mode 20,21 or (2) conversion of samples with high nitrite or nitrate concentrations to N 2 O via chemical or biological methods. 12 We have now successfully coupled an automated purge-and-trap and GC/IRMS (isotope/isotopomer measurements).…”

Section: Introductionmentioning

confidence: 99%

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

Grundle

2019

Rapid Comm Mass Spectrometry

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Rationale Nitrous oxide (N2O) is an atmospheric trace gas regulating Earth's climate, and is a key intermediate of many nitrogen cycling processes in aquatic ecosystems. Laser‐based technology for N2O concentration and isotopic/isotopomeric analyses has potential advantages, which include high analytical specificity, low sample size requirement and reduced cost. Methods An autosampler with a purge‐and‐trap module is coupled to a cavity ring‐down spectrometer to achieve automated and high‐throughput measurements of N2O concentrations, N2O isotope ratios (δ15Nbulk and δ18O values) and position‐specific isotopomer ratios (δ15Nα and δ15Nβ values). The system provides accuracy and precision similar to those for measurements made by traditional isotope ratio mass spectrometry (IRMS) techniques. Results The sample sizes required were 0.01–1.1 nmol‐N2O. Measurements of four N2O isotopic/isotopomeric references were cross‐calibrated with those obtained by IRMS. With a sample size of 0.50 nmol‐N2O, the measurement precision (1σ) for δ15Nα, δ15Nβ, δ15Nbulk and δ18O values was 0.61, 0.33, 0.41 and 0.43‰, respectively. Correction schemes were developed for sample size‐dependent isotopic/isotopomeric deviations. The instrumental system demonstrated consistent measurements of dissolved N2O concentrations, isotope/isotopomer ratios and production rates in seawater. Conclusions The coupling of an autosampler with a purge‐and‐trap module to a cavity ring‐down spectrometer not only significantly reduces sample size requirements, but also offers comprehensive investigation of N2O production pathways by the measurement of natural abundance and tracer level isotopes and isotopomers. Furthermore, the system can perform isotopic analyses of dissolved and solid nitrogen‐containing samples using N2O as the analytical proxy.

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Section: Introductionmentioning

confidence: 99%

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

Grundle

2019

Rapid Comm Mass Spectrometry

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“…CC BY 4.0 License. Mohn et al, 2013;Winther et al, 2018), and more recently to analyse diurnal and seasonal isotopic variations in ambient N2O (Mohn et al, 2012;Toyoda et al, 2013;Wolf et al, 2015;Harris et al, 2017). The isotopic composition of N2O emitted from soils can be extracted from ambient air measurements using traditional two end-member mixing models, i.e.…”

Section: Introductionmentioning

confidence: 99%

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

Ibraim¹,

Wolf²,

Harris³

et al. 2018

Preprint

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Abstract. Nitrous oxide (N2O) 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 N2O has increased from 270&#8201;ppb during the pre-industrial era to approx. 330&#8201;ppb in 2018. Even though it is well known that microbial processes in agricultural and natural soils are the major N2O source, the contribution of specific soil processes is still uncertain. The relative abundance of N2O isotopocules (14N14N16N, 14N15N16O, 15N14N16O and 14N14N18O) carries process-specific in-formation 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 N2O, quantum cascade laser absorption spectroscopy (QCLAS) has been put forward as a complementary technique with the potential for on-site analysis. In recent years, preconcentration combined with QCLAS has been presented as a technique to resolve subtle changes in ambient N2O isotopic composition. From the end of May until the beginning of August 2016, we investigated N2O emissions from an intensively managed grassland at the study site Fendt in Southern Germany. In total, 612 measurements of ambient N2O were taken by combining preconcentration with QCLAS analyses, yielding &#948;15N&#945;, &#948;15N&#946;, &#948;18O and N2O concentration with a temporal resolution of approximately one hour and precisions of 0.46&#8201;&#8240;, 0.36&#8201;&#8240;, 0.59&#8201;&#8240; and 1.24&#8201;ppb, respectively. Soil &#948;15N-NO3&#8722; values and concentrations of NO3&#8722; and NH4+ were measured to further constrain possible N2O-emitting source processes. Furthermore, the concentration footprint area of measured N2O was determined with a Lagrangian particle dispersion model (FLEXPART-COSMO) using local wind and turbulence observations. These simulations indicated that night-time concentration observations were largely sensitive to local fluxes. While bacterial denitrification and nitrifier denitrification were identified as the primary N2O-emitting processes, N2O reduction to N2 largely dictated the isotopic composition of measured N2O. Fungal denitrification and nitrification-derived N2O accounted for 34&#8211;42&#8201;% of total N2O emissions and had a clear effect on the measured isotopic source signatures. This study presents the suitability of on-site N2O isotopocule analysis for disentangling source and sink processes in-situ and found that at the Fendt site bacterial denitrification/nitrifier denitrification is the major source for N2O, while N2O reduction acted as a major sink.

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“…In cases where 15 calibrations are performed on the derived isotope ratios or δ values, [N2O] dependence corrections should span the range of expected N2O mole fractions and account for non-linear effects (e.g. Winther et al 2018). Alternative calibration approaches based on isotopocule concentrations or ratio calibration procedures were not included in our study, but have the potential to remove the need for this correction (e.g.…”

Section: Factors Affecting the Precision And Accuracy Of N2o Isotopocmentioning

confidence: 99%

“…These instruments can analyze the N2O isotopic composition in gaseous mixtures (e.g. ambient air) in a flow-through 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 (Decock and Six, 2013;Heil et al, 5 2014;Köster et al, 2013;Winther et al, 2018). Most importantly, MIR laser spectroscopy is selective for 17 O, 18 O and position-specific 15 N substitution due to the existence of characteristic rotationalvibrational spectra (Rothman et al, 2005).…”

Section: Introduction 20mentioning

confidence: 99%

“…To the best of our knowledge, the work presented in Lee et al (2017) and Ji and Grundle (2019) are the only published uses of G5131-i models. A prior model (the G5101-i), which employs a different 5 spectral region and does not offer the capability for  18 O was used by Peng et al (2014), Erler et al (2015), Li et al (2015), Lebegue et al (2016) and Winther et al (2018).…”

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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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Continuous measurements of nitrous oxide isotopomers during incubation experiments

Cited by 37 publications

References 46 publications

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

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

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Continuous measurements of nitrous oxide isotopomers during incubation experiments

Cited by 37 publications

References 46 publications

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

An automated, laser‐based measurement system for nitrous oxide isotope and isotopomer ratios at nanomolar levels

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

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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