Clumped isotope perturbation in tropospheric nitrous oxide from stratospheric photolysis

Schmidt, Johan A.; Johnson, Matthew S.

doi:10.1002/2015gl063102

Cited by 14 publications

(13 citation statements)

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“…Methane also plays a 53 central role in the chemistry of the troposphere and stratosphere (Harnung and 54 7 [ 13 CH 4 ][ 12 CH 3 D]). However, small (per mil level) deviations from this stochastic 116 distribution are observed due to thermodynamic (Ma et al, 2008;Stolper et al, 2014;117 Liu and Liu, 2016), kinetic (Wang et al, 2015), photolytic (Schmidt et al, 2013;Schmidt 118 and Johnson, 2015), and combinatorial (Yeung, 2016) effects. Stolper et al (2014) 119 hypothesize that there could be significant clumped kinetic isotope effects during the 120 photochemical methane sink reactions.…”

Section: Introduction 47mentioning

confidence: 99%

Clumped isotope effects during OH and Cl oxidation of methane

Whitehill

Joelsson

Schmidt

et al. 2017

Geochimica et Cosmochimica Acta

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23A series of experiments were carried out to determine the clumped ( 13 CH 3 D) 24 methane kinetic isotope effects during oxidation of methane by OH and Cl radicals, the 25 major sink reactions for atmospheric methane. Experiments were performed in a 100 L 26 quartz photochemical reactor, in which OH was produced from the reaction of O( 1 D) 27 (from O 3 photolysis) with H 2 O, and Cl was from photolysis of Cl 2 . Samples were taken 28 from the reaction cell and analyzed for methane ( 12 CH 4 , 12 CH 3 D, 13 CH 4 , 13 CH 3 D) 29 isotopologue ratios using tunable infrared differential laser absorption spectroscopy. 30Measured kinetic isotope effects for singly substituted species were consistent with 31 previous experimental studies. For doubly substituted methane, 13 CH 3 D, the observed 32 kinetic isotope effects closely follow the product of the kinetic isotope effects for the 13 C 33 and deuterium substituted species (i.e., 13,2 KIE = 13 KIE × 2 KIE). The deviation from this 34 relationship is 0.3‰ ± 1.2‰ and 3.5‰ ± 0.7‰ for OH and Cl oxidation, respectively. 35This is consistent with model calculations performed using quantum chemistry and 36 transition state theory. The OH and Cl reactions enrich the residual methane in the 37clumped isotopologue in open system reactions. In a closed system, however, this 38 effect is overtaken by the large D/H isotope effect, which causes the residual methane 39 to become anti-clumped relative to the initial methane. Based on these results, we 40 demonstrate that oxidation of methane by OH, the predominant oxidant for tropospheric 41 methane, will only have a minor (~0.3 ‰) impact on the clumped isotope signature 42 (Δ 13 CH 3 D, measured as a deviation from a stochastic distribution of isotopes) of 43 tropospheric methane. This paper shows that Δ 13 CH 3 D will provide constraints on 44 3 methane source strengths, and predicts that Δ 12 CH 2 D 2 can provide information on 45 methane sink strengths. 46 4

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Section: Introduction 47mentioning

confidence: 99%

Clumped isotope effects during OH and Cl oxidation of methane

Whitehill

Joelsson

Schmidt

et al. 2017

Geochimica et Cosmochimica Acta

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“…Clumped isotope geochemistry provides a new analytical tool for investigating several isotopic systems. Initially designed for carbonate thermometry, the application of clumped isotopes (both experimentally and theoretically) has expanded in recent times to incorporate other molecules such as CH 4 , C 2 H 6 , O 2 , NH 3 , H 2 O, H 2 S, SO 2 , and N 2 O . The methodology has advanced appreciably over the past decade in its application in geosciences, specifically in paleoclimate studies using carbonates.…”

Section: Introductionmentioning

confidence: 99%

Acid digestion of carbonates using break seal method for clumped isotope analysis

Fosu

Ghosh

Mishra

et al. 2018

Rapid Comm Mass Spectrometry

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Rationale: Acid digestion of carbonates to release CO 2 is a crucial and sensitive step in sample preparation for clumped isotope analysis. In addition to data reduction and instrumental artefacts, many other uncertainties in the clumped isotope analysis of carbonates arise from the method used for the preparation of CO 2 .We describe here an in-house-designed reaction vessel that circumvents degassing and contamination problems commonly associated with the McCrea-type digestion protocols. Methods:We designed a leak-free break seal reaction vessel (made of Pyrex™) suitable for prolonged acid digestion at 25°C. Using this new vessel, several carbonate reference materials widely used in the clumped isotope community and other inhouse laboratory standards were acid-digested and analysed for their δ 13 C, δ 18 O and Δ 47 values with a dual inlet MAT 253 isotope ratio mass spectrometer following standard gas chromatography purification and data evaluation protocols.Results: Long-term reproducibility in Δ 47 determination was established using international references and in-house working standards as follows (mean and SE):Carrara-1 (0.395 ± 0.002‰, n = 43), Carrara-2 (0.441 ± 0.003‰, n = 22), OMC (0.587 ± 0.004‰, n = 16), NBS 19 (0.393 ± 0.005‰, n = 10), NBS 18 (0.473 ± 0.003‰, n = 5), ETH 1 (0.271 ± 0.005‰, n = 7), ETH 3 (0.698 ± 0.005‰, n = 3), MZ (0.715 ± 0.002‰, n = 3) and several others. Conclusions:A new method using a break seal tube was found to be efficient for the clumped isotope analysis of carbonates that require longer reaction time at 25°C. This method yields good precision in Δ 47 analysis and was found to be suitable for acid digestions at any desired temperature.

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“…This is expected given the more rapid decline with altitude of the N 2 O VMR over the poles than in the tropics. The calculations of Schmidt and Johnson (2015) for midlatitudes ( Figure 2) also show the expected moderate fractionation with altitude. This enrichment is a measure of the age of air: polar air in the stratosphere is older, N 2 O is more photolyzed, and the heavier isotopologues are therefore relatively enriched.…”

Section: 1002/2017gl075122mentioning

confidence: 66%

“…This model was previously used for observing isotopologues of methane and CO , and a similar method is used here. .The other three panels show the corresponding δ values with one standard deviation error bars, as well as the midlatitude model values of Schmidt and Johnson (2015).…”

Section: Modelingmentioning

confidence: 99%

A Near‐Global Atmospheric Distribution of N₂O Isotopologues

Bernath

Yousefi

Buzan

et al. 2017

Geophysical Research Letters

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The distributions of the four most abundant isotopologues and isotopomers (N2O, 15NNO, N15NO, and NN18O) of nitrous oxide have been measured in the Earth's stratosphere by infrared remote sensing with the Atmospheric Chemistry Experiment (ACE) Fourier transform spectrometer. These satellite observations have provided a near‐global picture of N2O isotopic fractionation. The relative abundances of the heavier species increase with altitude and with latitude in the stratosphere as the air becomes older. The heavy isotopologues are enriched by 20–30% in the upper stratosphere and even more over the poles. These observations are in general agreement with model predictions made with the Whole Atmosphere Community Climate Model (WACCM). A detailed 3‐D chemical transport model is needed to account for the global isotopic distributions of N2O and to infer sources and sinks.

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Clumped isotope perturbation in tropospheric nitrous oxide from stratospheric photolysis

Cited by 14 publications

References 53 publications

Clumped isotope effects during OH and Cl oxidation of methane

Clumped isotope effects during OH and Cl oxidation of methane

Acid digestion of carbonates using break seal method for clumped isotope analysis

A Near‐Global Atmospheric Distribution of N₂O Isotopologues

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Clumped isotope perturbation in tropospheric nitrous oxide from stratospheric photolysis

Cited by 14 publications

References 53 publications

Clumped isotope effects during OH and Cl oxidation of methane

Clumped isotope effects during OH and Cl oxidation of methane

Acid digestion of carbonates using break seal method for clumped isotope analysis

A Near‐Global Atmospheric Distribution of N2O Isotopologues

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A Near‐Global Atmospheric Distribution of N₂O Isotopologues