Shipboard determinations of the distribution of 13C in atmospheric methane in the Pacific

Lowe, David C.; Allan, W.; Manning, Martin; Bromley, T.; Brailsford, Gordon; Ferretti, D. F.; Gomez, A. J.; Knobben, R. A.; Martin, Roderick; Mei, Zhu; Moss, Rowena; Koshy, Kanayathu; Maata, Matakite

doi:10.1029/1999jd900452

Cited by 51 publications

(58 citation statements)

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“…The high apparent KIE for CH 4 observed in the ETSH could be explained by a fraction of CH 4 being removed by reaction with chlorine atoms in the MBL as suggested by Lowe et al (1999) and Allan et al (2001a, b). The chlorine atom concentration in the MBL is required to have a seasonal cycle with an amplitude of about [Cl] max =6·10 3 atoms cm −3 (Allan et al, 2001b) equivalent to a 24 h average of [Cl] av,tot =2.6·10 3 atoms cm −3 .…”

Section: Discussionmentioning

confidence: 85%

“…To explain the high apparent KIE for methane observed in the ETSH, Lowe et al (1999) speculated that the removal process for methane might be enhanced by active chlorine in the marine boundary layer (MBL). Allan et al (2001b) used a simple chemical box model to show that the anomalously high KIE could be explained by assuming the existence of a seasonal cycle in active chlorine (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Hemispheric average Cl atom concentration from 13C/12C ratios in atmospheric methane

2004

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Abstract. Methane is a significant atmospheric trace gas in the context of greenhouse warming and climate change. The dominant sink of atmospheric methane is the hydroxyl radical (OH). Recently, a mechanism for production of chlorine radicals (Cl) in the marine boundary layer (MBL) via bromine autocatalysis has been proposed. The importance of this mechanism in producing a methane sink is not clear at present because of the difficulty of in-situ direct measurement of Cl. However, the large kinetic isotope effect of Cl compared with OH produces a large fractionation of 13 C compared with 12 C in atmospheric methane. This property can be used to estimate the likely minimum size of the methane sink attributable to MBL Cl. By taking account of the mixing of MBL air into the free troposphere, we estimate that the global methane sink due to reaction with Cl atoms in the MBL could be as large as 19 Tg yr −1 , or about 3.3% of the total CH 4 sink. However, its impact on the methane stable carbon isotope budget is large and warrants further attention.

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Section: Discussionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Hemispheric average Cl atom concentration from 13C/12C ratios in atmospheric methane

2004

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“…Samples were measured against laboratory working standard gases of pure CO 2 for δ 13 C-CH 4 and pure H 2 for δD-CH 4 . The δ 13 C-CH 4 calibration is based on a CO 2 reference gas provided by NIWA, which was compared with CO 2 produced from NBS-19 and IAEA-CO-9 (Lowe et al, 1999). The δD-CH 4 calibration is referenced to three H 2 gas cylinders purchased from Oztech Gas Company (Rice et al, 2001).…”

Section: Ucimentioning

confidence: 99%

Interlaboratory comparison of δ13C and δD measurements of atmospheric CH4 for combined use of data sets from different laboratories

et al. 2018

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Abstract. We report results from a worldwide interlaboratory comparison of samples among laboratories that measure (or measured) stable carbon and hydrogen isotope ratios of atmospheric CH 4 (δ 13 C-CH 4 and δD-CH 4 ). The offsets among the laboratories are larger than the measurement reproducibility of individual laboratories. To disentangle plausible measurement offsets, we evaluated and critically assessed a large number of intercomparison results, some of which have been documented previously in the literature. The results indicate significant offsets of δ 13 C-CH 4 and δD-CH 4 measurements among data sets reported from different laboratories; the differences among laboratories at modern atmospheric CH 4 level spread over ranges of 0.5 ‰ for δ 13 C-CH 4 and 13 ‰ for δD-CH 4 . The intercomparison results summarized in this study may be of help in future attempts to harmonize δ 13 C-CH 4 and δD-CH 4 data sets fromPublished by Copernicus Publications on behalf of the European Geosciences Union. 1208T. Umezawa et al.: Interlaboratory comparison of δ 13 C and δD measurements of CH 4 different laboratories in order to jointly incorporate them into modelling studies. However, establishing a merged data set, which includes δ 13 C-CH 4 and δD-CH 4 data from multiple laboratories with desirable compatibility, is still challenging due to differences among laboratories in instrument settings, correction methods, traceability to reference materials and long-term data management. Further efforts are needed to identify causes of the interlaboratory measurement offsets and to decrease those to move towards the best use of available δ 13 C-CH 4 and δD-CH 4 data sets.

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“…At Cl concentrations of 1×10 4 cm −3 the chemical lifetime of alkanes and alkynes towards this species is similar as that towards OH radicals (1×10 6 cm −3 ) (Finlayson-Pitts and Pitts, 2000). Results of measurements and estimates of chlorine radical concentrations in the marine BL of the tropics as well as the midlatitudes range two orders of magnitude ((0.25...30)×10 4 cm −3 , Singh et al, 1996;Wingenter et al, 1996;Lowe et al, 1999;von Glasow et al, 2002;Chang et al, 2004;Platt et al, 2004). Therefore a Cl concentration of 1×10 4 cm −3 was implemented in the reference run while additional sensitivity runs with the upper and lower limits were performed.…”

Section: Halogen Chemistrymentioning

confidence: 99%

Chemistry, transport and dry deposition of trace gases in the boundary layer over the tropical Atlantic Ocean and the Guyanas during the GABRIEL field campaign

et al. 2007

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Abstract. We present a comparison of different Lagrangian and chemical box model calculations with measurement data obtained during the GABRIEL campaign over the tropical Atlantic Ocean and the Amazon rainforest in the Guyanas, October 2005. Lagrangian modelling of boundary layer (BL) air constrained by measurements is used to derive a horizontal gradient (≈5.6 pmol/mol km −1 ) of CO from the ocean to the rainforest (east to west). This is significantly smaller than that derived from the measurements (16-48 pmol/mol km −1 ), indicating that photochemical production from organic precursors alone cannot explain the observed strong gradient. It appears that HCHO is overestimated by the Lagrangian and chemical box models, which include dry deposition but not exchange with the free troposphere (FT). The relatively short lifetime of HCHO implies substantial BL-FT exchange. The mixing-in of FT air affected by African and South American biomass burning at an estimated rate of 0.12 h −1 increases the CO and decreases the HCHO mixing ratios, improving agreement with measurements. A mean deposition velocity of 1.35 cm/s for H 2 O 2 over the ocean as well as over the rainforest is deduced assuming BL-FT exchange adequate to the results for CO. The measured increase of the organic peroxides from the ocean to the rainforest (≈0.66 nmol/mol d −1 ) is significantly overestimated by the Lagrangian model, even when using high values for the deposition velocity and the entrainment rate. Our results point at either heterogeneous loss of organic peroxides and/or their radical precursors, underestimated photodissociation or missing reaction paths of peroxy radicals not forming peroxides in isoprene chemistry. We calculate a mean integrated daytime net ozone production (NOP) in the Correspondence to: A. Stickler (alexander.stickler@env.ethz.ch) BL of (0.2±5.9) nmol/mol (ocean) and (2.4±2.1) nmol/mol (rainforest). The NOP strongly correlates with NO and has a positive tendency in the boundary layer over the rainforest.

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Shipboard determinations of the distribution of ¹³C in atmospheric methane in the Pacific

Cited by 51 publications

References 40 publications

Hemispheric average Cl atom concentration from <sup>13</sup>C/<sup>12</sup>C ratios in atmospheric methane

Hemispheric average Cl atom concentration from <sup>13</sup>C/<sup>12</sup>C ratios in atmospheric methane

Interlaboratory comparison of <i>δ</i><sup>13</sup>C and <i>δ</i>D measurements of atmospheric CH<sub>4</sub> for combined use of data sets from different laboratories

Chemistry, transport and dry deposition of trace gases in the boundary layer over the tropical Atlantic Ocean and the Guyanas during the GABRIEL field campaign

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Shipboard determinations of the distribution of 13C in atmospheric methane in the Pacific

Cited by 51 publications

References 40 publications

Hemispheric average Cl atom concentration from &lt;sup&gt;13&lt;/sup&gt;C/&lt;sup&gt;12&lt;/sup&gt;C ratios in atmospheric methane

Hemispheric average Cl atom concentration from &lt;sup&gt;13&lt;/sup&gt;C/&lt;sup&gt;12&lt;/sup&gt;C ratios in atmospheric methane

Interlaboratory comparison of &lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;13&lt;/sup&gt;C and &lt;i&gt;δ&lt;/i&gt;D measurements of atmospheric CH&lt;sub&gt;4&lt;/sub&gt; for combined use of data sets from different laboratories

Chemistry, transport and dry deposition of trace gases in the boundary layer over the tropical Atlantic Ocean and the Guyanas during the GABRIEL field campaign

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Shipboard determinations of the distribution of ¹³C in atmospheric methane in the Pacific

Hemispheric average Cl atom concentration from <sup>13</sup>C/<sup>12</sup>C ratios in atmospheric methane

Hemispheric average Cl atom concentration from <sup>13</sup>C/<sup>12</sup>C ratios in atmospheric methane

Interlaboratory comparison of <i>δ</i><sup>13</sup>C and <i>δ</i>D measurements of atmospheric CH<sub>4</sub> for combined use of data sets from different laboratories