scholarly journals Evaluating Chlorine Isotope Effects from Isotope Ratios and Mass Spectra of Polychlorinated Molecules

2008 ◽  
Vol 80 (12) ◽  
pp. 4731-4740 ◽  
Author(s):  
Martin Elsner ◽  
Daniel Hunkeler
Keyword(s):  
Mass Spectra ◽  
Isotope Effects ◽  
Isotope Ratios ◽  
Chlorine Isotope

scholarly journals Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

2014 ◽  
Vol 14 (23) ◽  
pp. 31813-31841
Author(s):  
S. J. Allin ◽  
J. C. Laube ◽  
E. Witrant ◽  
J. Kaiser ◽  
E. McKenna ◽  
...  
Keyword(s):  
Isotope Fractionation ◽  
Isotope Composition ◽  
Stratospheric Ozone ◽  
Isotope Ratios ◽  
Gas Chromatography Mass Spectrometry ◽  
Chlorine Isotope ◽  
Site Model ◽  
Tropospheric Measurements ◽  
Single Detector

Abstract. The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (ϵapp) for mid- and high-latitude stratospheric samples are (−2.4 ± 0.5) and (−2.3 ± 0.4)‰ for CFC-11, (−12.2 ± 1.6) and (−6.8 ± 0.8)‰ for CFC-12 and (−3.5 ± 1.5) and (−3.3 ± 1.2)‰ for CFC-113, respectively. Assuming a constant source isotope composition, we estimate the expected trends in the tropospheric isotope signature of these gases due to their stratospheric 37Cl enrichment and stratosphere–troposphere exchange. We compare these model results to the long-term δ(37Cl) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978–2010) and tropospheric firn air samples from Greenland (NEEM site) and Antarctica (Fletcher Promontory site). Model trends agree with tropospheric measurements within analytical uncertainties. From 1970 to the present-day, we find no evidence for variations in chlorine isotope ratios associated with changes in CFC manufacturing processes. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes, using a single-detector gas chromatography-mass spectrometry system.

scholarly journals Nitrogen and Oxygen Isotope Effects of Ammonia Oxidation by Thermophilic Thaumarchaeota from a Geothermal Water Stream

2016 ◽  
Vol 82 (15) ◽  
pp. 4492-4504 ◽  
Author(s):  
Manabu Nishizawa ◽  
Sanae Sakai ◽  
Uta Konno ◽  
Nozomi Nakahara ◽  
Yoshihiro Takaki ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Ammonia Oxidation ◽  
Isotope Effects ◽  
Isotope Ratios ◽  
Oxidation Activity ◽  
Content Type ◽  
Ammonia Oxidizing Archaea ◽  
Nitrogen Pools ◽  
Archaeal Ammonia Oxidation

ABSTRACTAmmonia oxidation regulates the balance of reduced and oxidized nitrogen pools in nature. Although ammonia-oxidizing archaea have been recently recognized to often outnumber ammonia-oxidizing bacteria in various environments, the contribution of ammonia-oxidizing archaea is still uncertain due to difficulties in thein situquantification of ammonia oxidation activity. Nitrogen and oxygen isotope ratios of nitrite (δ15NNO2−and δ18ONO2−, respectively) are geochemical tracers for evaluating the sources and thein siturate of nitrite turnover determined from the activities of nitrification and denitrification; however, the isotope ratios of nitrite from archaeal ammonia oxidation have been characterized only for a few marine species. We first report the isotope effects of ammonia oxidation at 70°C by thermophilicThaumarchaeotapopulations composed almost entirely of “CandidatusNitrosocaldus.” The nitrogen isotope effect of ammonia oxidation varied with ambient pH (25‰ to 32‰) and strongly suggests the oxidation of ammonia, not ammonium. The δ18O value of nitrite produced from ammonia oxidation varied with the δ18O value of water in the medium but was lower than the isotopic equilibrium value in water. Because experiments have shown that the half-life of abiotic oxygen isotope exchange between nitrite and water is longer than 33 h at 70°C and pH ≥6.6, the rate of ammonia oxidation by thermophilicThaumarchaeotacould be estimated using δ18ONO2−in geothermal environments, where the biological nitrite turnover is likely faster than 33 h. This study extended the range of application of nitrite isotopes as a geochemical clock of the ammonia oxidation activity to high-temperature environments.IMPORTANCEBecause ammonia oxidation is generally the rate-limiting step in nitrification that regulates the balance of reduced and oxidized nitrogen pools in nature, it is important to understand the biological and environmental factors underlying the regulation of the rate of ammonia oxidation. The discovery of ammonia-oxidizing archaea (AOA) in marine and terrestrial environments has transformed the concept that ammonia oxidation is operated only by bacterial species, suggesting that AOA play a significant role in the global nitrogen cycle. However, the archaeal contribution to ammonia oxidation in the global biosphere is not yet completely understood. This study successfully identified key factors controlling nitrogen and oxygen isotopic ratios of nitrite produced from thermophilicThaumarchaeotaand elucidated the applicability and its limit of nitrite isotopes as a geochemical clock of ammonia oxidation rate in nature. Oxygen isotope analysis in this study also provided new biochemical information on archaeal ammonia oxidation.

The photo-Wallach rearrangement. Heavy-atom kinetic isotope effects and mechanism

1986 ◽  
Vol 64 (6) ◽  
pp. 1108-1115 ◽  
Author(s):  
Henry J. Shine ◽  
Witold Subotkowski ◽  
Ewa Gruszecka
Keyword(s):  
Activation Barrier ◽  
Isotope Effects ◽  
Heavy Atom ◽  
Isotope Ratios ◽  
Kinetic Isotope Effects ◽  
Isotopic Ratios ◽  
Kinetic Isotope

The photo-rearrangement of mixtures of azoxybenzene 4 and, successively, [15N, 15N′]4, [18O]4, and [2-14C]4 were carried out. Kinetic isotope effects (KIE) were calculated from measurements of isotopic ratios in both recovered 4 and the product, 2-hydroxyazobenzene (6). Analogous rearrangement of mixtures of 2,2′-azoxynaphthalene (8) with [15N, 15N′]8 and [1,1′-13C2]8 were carried out and KIE were calculated from isotope ratios in the product. The results (particularly the lack of nitrogen KIE) collectively indicate that if an oxadiazole-like intermediate is involved in these rearrangements, an activation barrier exists in its formation rather than its decomposition.

scholarly journals Nitrogen and oxygen isotopic constraints on the origin of atmospheric nitrate in coastal Antarctica

2007 ◽  
Vol 7 (8) ◽  
pp. 1925-1945 ◽  
Author(s):  
J. Savarino ◽  
J. Kaiser ◽  
S. Morin ◽  
D. M. Sigman ◽  
M. H. Thiemens
Keyword(s):  
Isotopic Composition ◽  
Oxygen Isotope ◽  
Transition Period ◽  
Isotope Effects ◽  
Isotope Ratios ◽  
Background Concentration ◽  
Night Time ◽  
Oxygen Isotope Ratios ◽  
Period 2 ◽  
Oxygen Isotopic

Abstract. Throughout the year 2001, aerosol samples were collected continuously for 10 to 15 days at the French Antarctic Station Dumont d'Urville (DDU) (66°40' S, l40°0' E, 40 m above mean sea level). The nitrogen and oxygen isotopic ratios of particulate nitrate at DDU exhibit seasonal variations that are among the most extreme observed for nitrate on Earth. In association with concentration measurements, the isotope ratios delineate four distinct periods, broadly consistent with previous studies on Antarctic coastal areas. During austral autumn and early winter (March to mid-July), nitrate concentrations attain a minimum between 10 and 30 ng m−3 (referred to as Period 2). Two local maxima in August (55 ng m−3) and November/December (165 ng m−3) are used to assign Period 3 (mid-July to September) and Period 4 (October to December). Period 1 (January to March) is a transition period between the maximum concentration of Period 4 and the background concentration of Period 2. These seasonal changes are reflected in changes of the nitrogen and oxygen isotope ratios. During Period 2, which is characterized by background concentrations, the isotope ratios are in the range of previous measurements at mid-latitudes: δ18Ovsmow=(77.2±8.6)‰; Δ17O=(29.8±4.4)‰; δ15Nair=(−4.4±5.4)‰ (mean ± one standard deviation). Period 3 is accompanied by a significant increase of the oxygen isotope ratios and a small increase of the nitrogen isotope ratio to δ18Ovsmow=(98.8±13.9)‰; Δ17O=(38.8±4.7)‰ and δ15Nair=(4.3±8.20‰). Period 4 is characterized by a minimum 15N/14N ratio, only matched by one prior study of Antarctic aerosols, and oxygen isotope ratios similar to Period 2: δ18Ovsmow=(77.2±7.7)‰; Δ17O=(31.1±3.2)‰; δ15Nair=(−32.7±8.4)‰. Finally, during Period 1, isotope ratios reach minimum values for oxygen and intermediate values for nitrogen: δ18Ovsmow=63.2±2.5‰; Δ17O=24.0±1.1‰; δ15Nair=−17.9±4.0‰). Based on the measured isotopic composition, known atmospheric transport patterns and the current understanding of kinetics and isotope effects of relevant atmospheric chemical processes, we suggest that elevated tropospheric nitrate levels during Period 3 are most likely the result of nitrate sedimentation from polar stratospheric clouds (PSCs), whereas elevated nitrate levels during Period 4 are likely to result from snow re-emission of nitrogen oxide species. We are unable to attribute the source of the nitrate during periods 1 and 2 to local production or long-range transport, but note that the oxygen isotopic composition is in agreement with day and night time nitrate chemistry driven by the diurnal solar cycle. A precise quantification is difficult, due to our insufficient knowledge of isotope fractionation during the reactions leading to nitrate formation, among other reasons.

Carbon and Chlorine Isotope Effects During Abiotic Reductive Dechlorination of Polychlorinated Ethanes

2007 ◽  
Vol 41 (13) ◽  
pp. 4662-4668 ◽  
Author(s):  
Thomas B. Hofstetter ◽  
Christopher M. Reddy ◽  
Linnea J. Heraty ◽  
Michael Berg ◽  
Neil C. Sturchio
Keyword(s):  
Reductive Dechlorination ◽  
Isotope Effects ◽  
Chlorine Isotope
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