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Chloromethane (CH3Cl) is the most abundant natural chlorinated organic compound in the atmosphere playing an important role in catalyzing stratospheric ozone loss. Vegetation emits the largest amounts of CH3Cl to the atmosphere but its source strength is highly uncertain leading also to large uncertainties in the global budget of CH3Cl. Triple‐element stable isotope analysis may help to reduce uncertainties because it provides additional process‐level information compared to conventional quantification methods. In this study we performed experiments to obtain a first triple‐elemental isotopic fingerprint (2H, 13C, 37Cl) of CH3Cl emitted by a relevant plant species (royal fern, Osmunda regalis). Isotopic values of all three elements showed considerable differences compared to isotopic values of industrially manufactured CH3Cl which bodes well for future applications to distinguish individual sources. Isotopic analysis of potential precursors (rain, methoxy groups) of CH3Cl in plants revealed no measurable change of hydrogen and chlorine isotopic ratios during formation which may provide a simpler route to estimate the isotopic composition of CH3Cl emissions. Plant degradation experiments of CH3Cl were carried out with club moss (Selaginella kraussiana) revealing significant isotopic fractionation for all three elements. The fractionation pattern characterized by epsilon and lambda is inconsistent with known biotic dechlorination reactions indicating a yet unreported biotic degradation mechanism for CH3Cl. Overall, this study provides first insights into the triple‐elemental isotopic fingerprint of plant emissions and degradation. The results may represent important input data for future isotope‐based models to improve global budget estimates of CH3Cl and to explore the yet unknown degradation pathways. Plain Language Summary: Chloromethane is the most abundant chlorinated organic compound in the atmosphere. It contributes to the destruction of the ozone layer that protects us from skin cancer and genetic damage. Currently, we do not have a good understanding of the sources and removal processes of chloromethane in the atmosphere. In this paper, we use a technique that takes advantage of the different varieties of a chemical element. These so‐called isotopes behave differently during chemical reactions that lead to individual isotopic fingerprints depending on the source or removal process. We used isotopic fingerprints of all three chemical elements in chloromethane and showed that chloromethane produced by a plant (royal fern) differs substantially from chloromethane manufactured by industry. Other plant species such as club moss are able to remove chloromethane from the atmosphere but it is often not clear how this occurs. Isotopic analysis revealed that the studied club moss uses a unique, thus far unknown, way to break down chloromethane. This study demonstrates how information extracted from isotopic fingerprints will help to improve our understanding of sources and removal processes of chloromethane in the atmosphere. It can help to better predict how ozone destruction in the stratosphere affects us in the future. Key Points: First triple‐element isotopic characterization of plant CH3Cl emission and degradationPlant degradation experiments suggest another yet unknown transformation pathwayImportant input data for future isotope based models to improve understanding of global CH3Cl budget [ABSTRACT FROM AUTHOR]

Transfer of organic compounds between aqueous and gaseous phases may change the isotopic composition which complicates the isotopic characterization of sources and transformation mechanisms in environmental samples. Studies investigating kinetic phase transfer of compounds dissolved in water (volatilization) are scarce, even though it presents an environmentally very relevant phase transfer scenario. In the current study, the occurrence of kinetic isotope fractionation (2H/1H, 13C/12C, 37Cl/35Cl) was investigated for two volatile organic compounds (trichloroethene, TCE and trichloromethane, TCM) during volatilization from water and gas-phase dissolution in water. In addition, experiments were also carried out at equilibrium conditions. The results indicated that volatilization of trichloromethane and trichloroethene from water, in contrast to pure phase evaporation, only caused small (chlorine) or negligible (hydrogen, carbon) isotope fractionation whereas for dissolution in water significant carbon isotope effects were found. At equilibrium conditions, hydrogen and carbon isotopes showed significant differences between dissolved and gaseous phase whereas small to insignificant differences were measured for chlorine isotopes. The results confirm the hypothesis that isotope effects during volatilization of organics from water are caused by transport inhibition in the aqueous phase. The consideration of gas-phase diffusion and vapor pressure isotope effects (Craig–Gordon model) could not reproduce the measured isotopic data. Overall, this study provides an overview of the most common kinetic and equilibrium partitioning scenarios and reports associated isotope effects. As such it illustrates under which environmental conditions isotopic signatures of chlorinated volatile organics may change, or remain constant, during transfer between surface waters and air. [ABSTRACT FROM AUTHOR]

Stable chlorine isotope analysis of organic compounds is potentially applicable in various fields in forensics and environmental analytics to investigate the fate of these substances in the environment, but a wider use of this technique is still hampered by the limited applicability of available offline and online techniques. In a previous study we presented a method for compound-specific chlorine isotope analysis of volatile organics including chlorinated methanes, ethanes and ethenes using gas chromatography interfaced with multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS). In the current study we modified further the setup in order to extend the range of analytes towards semi-volatile organic substances with boiling points of up to 350 °C. The modified method was evaluated by using offline characterized in-house reference materials, such as chloroethenes, chloroacetic acid and hexachlorocyclohexenes. Additionally, analysis of various chlorinated benzenes, chlorinated phenols, chlordecone, dichlorodiphenyltrichloroethane (DDT) and related derivatives was demonstrated. The analytical precision (1σ) was usually better than ±0.2 mUr for single compound and ±0.3 mUr for compound-specific analysis of mixtures. Achieved accuracy was within ±0.2 mUr compared to available offline values. The isotopic detection limit could be significantly improved by one order of magnitude (250 pmol Cl on column, corresponding to ∼10 ng Cl) and is superior to other online state of the art approaches. The demonstrated method allows for the compound-specific stable chlorine isotope analysis of virtually all GC-compatible organics with versatility, high accuracy, and sensitivity. [ABSTRACT FROM AUTHOR]

Stable chlorine isotope analysis is increasingly used to characterize sources, transformation pathways, and sinks of organic aliphatic compounds, many of them being priority pollutants in groundwater and the atmosphere. A wider use of chlorine isotopes in environmental studies is still inhibited by limitations of the different analytical techniques such as high sample needs, offline preparation, confinement to few compounds and mediocre precision, respectively. Here we present a method for the d[sup 37]Cl determination in volatile aliphatic compounds using gas chromatography coupled with multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS), which overcomes these limitations. The method was evaluated by using a suite of five previously offline characterized in-house standards and eight chlorinated methanes, ethanes, and ethenes. Other than in previous approaches using ICP methods for chlorine isotopes, isobaric interference of the [sup 36]ArH dimer with [sup 37]Cl was minimized by employing dry plasma conditions. Samples containing 2-3 nmol Cl injected on-column were sufficient to achieve a precision (s) of 0.1 mUr (1 milliurey = 0.001 = 1‰) or better. Long-term reproducibility and accuracy was always better than 0.3 mUr if organics were analyzed in compound mixtures. Standardization is carried out by using a two-point calibration approach. Drift, even though very small in this study, is corrected by referencing versus an internal standard. The presented method offers a direct, universal, and compound-specific procedure to measure the d[sup 37]Cl of a wide array of organic compounds overcoming limitations of previous techniques with the benefits of high sensitivity and accuracy comparable to the best existing approaches. [ABSTRACT FROM AUTHOR]

Volatilization causes changes in the isotopic composition of organic compounds as a result of different vapor pressures of molecules containing heavy and light isotopes. Both normal and inverse vapor pressure isotope effects (VPIE) have been observed, depending on molecular interactions in the liquid phase and the investigated element. Previous studies have focused mostly on pure compound volatilization or on compounds dissolved in organic liquids. Environmentally relevant scenarios, such as isotope fractionation during volatilization of organics from open water surfaces, have largely been neglected. In the current study, open-system volatilization experiments (focusing thereby on kinetic/ -nonequilibrium effects) were carried out at ambient temperatures for trichloromethane, trichloroethene, trichlorofluoromethane, trichlorotrifluoroethane, methanol, and ethanol dissolved in water and, if not previously reported in the literature for these compounds, for volatilization from pure liquids. Stable carbon isotopic signatures were measured using continuous flow isotope ratio mass spectrometry. The results demonstrate that volatilization of the four halogenated compounds from water does not cause a measurable change in the carbon isotopic composition, whereas for pure-phase evaporation, significant inverse isotope effects are consistently observed (+0.3 ‰ < ε < + 1.7 ‰). In contrast, methanol and ethanol showed normal isotope effects for evaporation of pure organic liquids (-3.9 ‰ and -1.9‰) and for volatilization of compounds dissolved in water (-4.4 ‰ and -2.9 ‰), respectively. This absence of measurable carbon isotope fractionation considerably facilitates the application of isotopic techniques for extraction of field samples and preconcentration of organohalogens known to be important pollutants in groundwater and in the atmosphere. [ABSTRACT FROM AUTHOR]

Methyl chloride and methyl bromide (CH 3 Cl and CH 3 Br) are the largest natural sources of chlorine and bromine, respectively, to the stratosphere, where they contribute to ozone depletion. We report the anthropogenic production of CH 3 Cl and CH 3 Br during breadbaking, and suggest this production is an abiotic process involving the methyl ester functional groups in pectin and lignin structural polymers of plant cells. Wide variations in baking styles allow only rough estimates of this flux of methyl halides on a global basis. A simple model suggests that CH 3 Br emissions from breadbaking likely peaked circa 1990 at approximately 200 tonnes per year (about 0.3% of industrial production), prior to restrictions on the dough conditioner potassium bromate. In contrast, CH 3 Cl emissions from breadbaking may be of similar magnitude as acknowledged present-day CH 3 Cl industrial emissions. Because the mechanisms involve functional groups and compounds widely found in plant materials, this type of methyl halide production may occur in other cooking techniques as well. [ABSTRACT FROM AUTHOR]

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), controlled substances due to their role in stratospheric ozone loss, also occur as dissolved contaminants in groundwaters. Stable carbon isotopic signatures may provide valuable new information on the fate of these compounds as has been seen for other priority hydrocarbon contaminants, but to date no method for extraction and isotopic analysis of dissolved CFCs from groundwaters has been developed. Here we describe a cryogenic purge and trap system coupled to continuous flow compound-specific stable carbon isotope analysis mass spectrometry for concentrations as low as 35 µg/L. The method is validated by comparing isotopic signatures from water extracted CFCs against a new suite of isotopic CFC standards. Fractionation of CFCs in volatilization experiments from pure-phase CFC-11 and CFC-113 resulted in enrichment factors (ε) of +1.7 ± 0.1‰ and +1.1 ± 0.1‰, respectively, indicating that such volatile loss, if significant, would produce a more 13C depleted signature in the remaining CFCs. Importantly, no significant fractionation was observed during volatile extraction of dissolved CFCs from aqueous solutions. δ13C values for groundwaters from a CFC-contaminated site were, on average, more enriched than δ13C values for pure compounds. Such enriched δ13C values have been seen in other hydrocarbon contaminants such as chlorinated ethenes and ethanes due to in situ degradation, but definitive interpretation of such enriched signatures in field samples requires additional experiments to characterize fractionation of CFCs during biodegradation. The establishment of a robust and sensitive method of extraction and analysis, as described here, provides the foundation for such future directions. [ABSTRACT FROM AUTHOR]

Methyl bromide (CH3Br) emitted from plants constitutes a natural source of bromine to the atmosphere, and is a component in the currently unbalanced global CH3Br budget. In the stratosphere, CH3Br contributes to ozone loss processes. Studies of stable isotope composition may reduce uncertainties in the atmospheric CH3Br budget, but require well-constrained isotope fingerprints of the source end members. Here we report the first measurements of stable bromine isotopes (δ81Br) in CH3Br from abiotic plant emissions. Incubations of both KBr-fortified pectin, a ubiquitous cell-stabilizing macromolecule, and of a natural halophyte (Salicornia fruticosa), yielded an enrichment factor (ε) of −2.00±0.23‰ (1σ, n =8) for pectin and −1.82±0.02‰ (1σ, n =4) for Salicornia (the relative amount of the heavier 81Br was decreased in CH3Br compared to the substrate salt). For short incubations, and up to 10% consumption of the salt substrate, this isotope effect was similar for temperatures from 30 up to 300°C. For longer incubations of up to 90h at 180°C the δ81Br values increased from −2‰ to 0‰ for pectin and to −1‰ for Salicornia. These δ81Br source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget. [ABSTRACT FROM AUTHOR]

A system was developed for collecting from the ambient atmosphere the methyl halides CH3Cl and CH3Br in quantities sufficient for chlorine and bromine isotope analysis. The construction and operation of the novel cryogenic collection system (cryosampler) and sample purification system developed for this task are described. This study demonstrates the capability of the cryosampler by quantifying the CH3Cl and CH3Br collected from atmospheric samples and the nonfractionating bromine isotope fingerprint of CH3Br from synthetic air samples of controlled composition. An optimized cryosampler operation time of 4 h at a flow rate of 15 L min−1 is applied to yield the nearly 40 ng required for subsequent δ81Br-CH3Br analyses. The sample purification system is designed around a packed column gas chromatography-quadropole-mass spectrometry (GCqMS) system with three additional cryotraps and backflushing capacity. The system's suitability was tested by observing both the mass recovery and the lack of Δ81Br isotope fractionation induced during sample purification under varying flow rates and loading scenarios. To demonstrate that the entire system samples and dependably delivers CH3Br to the isotope analysis system without inducing isotope fractionation, diluted synthetic air mixtures prepared from standard gases were processed through the entire system, yielding a Δ81Br-CH3Br of +0.03‰ ± 0.10‰ relative to their starting composition. Finally, the combined cryosampler-purification and analysis system was applied to demonstrate the first-ever δ81Br-CH3Br in the ambient atmosphere with two samples collected in the autumn of 2011, yielding −0.08‰ ± 0.43‰ and +1.75‰ ± 0.13‰ versus standard mean ocean bromide for samples collected at a suburban Stockholm, Sweden, site. [ABSTRACT FROM AUTHOR]

Tropospheric methyl bromide (CH3Br) is the largest source of bromine to the stratosphere and plays an important role in ozone depletion. Here, the first stable bromine isotope composition (δ81Br) of atmospheric CH3Br is presented. The δ81Br of higher concentration Stockholm samples and free air subarctic Abisko samples suggest a source/background value of −0.04±0.28‰ ranging up to +1.75±0.12‰. The Stockholm δ81Br versus concentration relationship corresponds to an apparent isotope enrichment factor of −4.7±3.7‰, representing the combined reaction sink. This study demonstrates the scientific potential of atmospheric δ81Br measurements, which in the future may be combined with other isotope systems in a top-down inverse approach to further understand key source and sink processes of methyl bromide. [ABSTRACT FROM AUTHOR]

The article presents a study on the groundwater geochemistry of the Chihuahua City region in the Rio Conchos Basin in northern Mexico, and its implications for water resources management. Results showed that the background groundwater chemistry upstream of Chihuahua City results from feldspar weathering but beyond Chihuahua City, the chemical conditions are strongly modified owing to the disposal of sewage from public and industrial water supplie into the Rio Chuviscar. As a consequence, anions like chloride and and sulphate are mainly linked to surface sources, while nitrate is controlled in part by sewage from public supply and industry and in part by agricultural practices.

Stable Isotopes (strontium-87, deuterium and oxygen-18, carbon-13) have been used to reveal different sources of groundwater and mixing processes in the aquifer of the Silao-Romita Valley in the state of Guanajuato, Mexico. Calcite dissolution appeared to be the main process of strontium release leading to relatively equal 87Sr/86Sr ratios of 0.7042-0.7062 throughout the study area which could be confirmed by samples of carbonate rocks having similar Sr ratios (0.7041-0.7073). δ13C values (-11.91- -6.87‰ VPDB) of groundwaters confirmed the solution of carbonates but indicated furthermore influences of soil-CO2. Deuterium and 18O contents showed a relatively narrow range of-80.1- -70.0 ‰ VSMOW and-10.2- -8.8 ‰, VSMOW, respectively but are affected by evaporation and mixing processes. The use of δ13C together with 87Sr/86Sr revealed three possible sources: (i) carbonate-controlled waters showing generally higher Sr-concentrations, (ii) fissure waters with low-strontium contents and (iii) infiltrating water which is characterized by low δ13C and 87Sr/86Sr ratios. The third component is affected by evaporation processes taking place before and during infiltration which might be increased by extraction and reinfiltration (irrigation return flow). [ABSTRACT FROM AUTHOR]

Elemental analysis (EA) coupled to isotope ratio mass spectrometry (IRMS) is a well-established method to derive stable isotope ratios of sulfur ( 34 S/ 32 S). Conversion of sulfur to SO 2 by EA and measurement of SO 2 isotopologues by IRMS represents the simplest and most versatile method to accomplish isotope measurement of sulfur even in bulk samples. Yet, interferences by oxygen isotopes in SO 2 often impair the precision and trueness of measured results. In the current study, we coupled EA to multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) to establish a method that avoids such interferences due to direct measurement of S + ions. In addition, measurement of the 33 S/ 32 S isotope ratios is possible, thus representing the first bulk method that is suitable to study mass-independent isotope fractionation (MIF). Analytical precision (σ) of available Ag 2 S and BaSO 4 reference materials (RMs) was, on average, 0.2 mUr for δ 33 S and δ 34 S, never exceeding 0.3 mUr within this study (1 mUr = 1‰ = 0.001). Measured δ 34 S values of reference materials agreed within ±0.2 mUr of officially reported values. Measurement of wood samples yielded good precision (0.2 mUr) for sulfur amounts as low as 3.5 μg, but precision deteriorated for samples at lower sulfur contents due to poor peak shape. Finally, we explored cross-calibration of organic liquids separated via gas chromatography (GC) against solid RMs combusted via EA that avoids challenging offline conversion of RMs. Results indicate good precision (≤0.08 mUr) and acceptable trueness (≤0.34 mUr) for determination of δ 34 S, demonstrating the future potential of such an approach.

Compound-specific isotope analysis of sulfur (δ 34 S-CSIA) in organic compounds was established in the last decade employing gas chromatography connected to multiple-collector inductively coupled plasma mass spectrometry (GC-MC-ICPMS). However, δ 33 S-CSIA has not yet been reported so far. In this study, we present a method for the simultaneous determination of δ 33 S and δ 34 S in organic compounds by GC-MC-ICPMS applying medium- and also low-mass-resolution modes. The method was validated using the international isotope reference materials IAEA-S-1, IAEA-S-2, and IAEA-S-3. Overall analytical uncertainty including normalization and reproducibility for δ 33 S and δ 34 S was usually better than ±0.2 mUr (σ) for analytes containing at least 100 pmol of S. Further, it is demonstrated that, despite small isobaric interferences, results obtained at low mass resolution are indistinguishable from medium mass resolution offering the benefit of increased sensitivity and versatility of this method. Additionally, the method was applied for the δ 33 S and δ 34 S isotope analysis of industrially produced organic compounds to investigate potential mass-independent fractionation (MIF). The relation between δ 34 S and δ 33 S in these compounds followed a mass-dependent fractionation trend (MDF; Δ 33 S ≤ ±0.2 mUr). Degradation of dimethyl disulfide by direct photolysis caused a small but significant MIF (Δ 33 S = 0.55 ± 0.04 mUr, n = 3), demonstrating sufficient sensitivity of the method for these types of studies.

Transfer of organic compounds between aqueous and gaseous phases may change the isotopic composition which complicates the isotopic characterization of sources and transformation mechanisms in environmental samples. Studies investigating kinetic phase transfer of compounds dissolved in water (volatilization) are scarce, even though it presents an environmentally very relevant phase transfer scenario. In the current study, the occurrence of kinetic isotope fractionation ( 2 H/ 1 H, 13 C/ 12 C, 37 Cl/ 35 Cl) was investigated for two volatile organic compounds (trichloroethene, TCE and trichloromethane, TCM) during volatilization from water and gas-phase dissolution in water. In addition, experiments were also carried out at equilibrium conditions. The results indicated that volatilization of trichloromethane and trichloroethene from water, in contrast to pure phase evaporation, only caused small (chlorine) or negligible (hydrogen, carbon) isotope fractionation whereas for dissolution in water significant carbon isotope effects were found. At equilibrium conditions, hydrogen and carbon isotopes showed significant differences between dissolved and gaseous phase whereas small to insignificant differences were measured for chlorine isotopes. The results confirm the hypothesis that isotope effects during volatilization of organics from water are caused by transport inhibition in the aqueous phase. The consideration of gas-phase diffusion and vapor pressure isotope effects (Craig-Gordon model) could not reproduce the measured isotopic data. Overall, this study provides an overview of the most common kinetic and equilibrium partitioning scenarios and reports associated isotope effects. As such it illustrates under which environmental conditions isotopic signatures of chlorinated volatile organics may change, or remain constant, during transfer between surface waters and air.

Chloromethane (CH 3 Cl) is an important source of chlorine in the stratosphere, but detailed knowledge of the magnitude of its sources and sinks is missing. Here, we measured the stable chlorine isotope fractionation (ε Cl ) associated with the major abiotic and biotic CH 3 Cl sinks in the environment, namely, CH 3 Cl degradation by hydroxyl ( · OH) and chlorine ( · Cl) radicals in the troposphere and by reference bacteria Methylorubrum extorquens CM4 and Leisingera methylohalidivorans MB2 from terrestrial and marine environments, respectively. No chlorine isotope fractionation was detected for reaction of CH 3 Cl with · OH and · Cl radicals, whereas a large chlorine isotope fractionation (ε Cl ) of -10.9 ± 0.7‰ ( n = 3) and -9.4 ± 0.9 ( n = 3) was found for CH 3 Cl degradation by M. extorquens CM4 and L. methylohalidivorans MB2, respectively. The large difference in chlorine isotope fractionation observed between tropospheric and bacterial degradation of CH 3 Cl provides an effective isotopic tool to characterize and distinguish between major abiotic and biotic processes contributing to the CH 3 Cl sink in the environment. Our findings demonstrate the potential of emerging triple-element isotopic approaches including chlorine to carbon and hydrogen analysis for the assessment of global cycling of organochlorines.

Compound-specific isotope analysis (CSIA) is a valuable tool in contaminant remediation studies. Chlorofluorocarbons (CFCs) are ozone-depleting substances previously thought to be persistent in groundwater under most geochemical conditions but more recently have been found to (bio)transform in some laboratory experiments. To date, limited applications of CSIA to CFCs have been undertaken. Here, biotransformation-associated carbon isotope enrichment factors, ε C,bulk for CFC-113 (ε C,bulk = -8.5 ± 0.4‰) and CFC-11 (ε C,bulk = -14.5 ± 1.9‰), were determined. δ 13 C signatures of pure-phase CFCs and hydrochlorofluorocarbons were measured to establish source signatures. These findings were applied to investigate potential in situ CFC transformation in groundwater at a field site, where carbon isotope fractionation of CFC-11 suggests naturally occurring biotransformation by indigenous microorganisms. The maximum extent of CFC-11 transformation is estimated to be up to 86% by an approximate calculation using the Rayleigh concept. CFC-113 δ 13 C values in contrast were not resolvably different from pure-phase sources measured to date, demonstrating that CSIA can aid in identifying which compounds may, or may not, be undergoing reactive processes at field sites. Science and public attention remains focused on CFCs, as unexplained source inputs to the atmosphere have been recently reported, and the potential for CFC biotransformation in surface and groundwaters remains unclear. This study proposes δ 13 C CSIA as a novel application to study the fate of CFCs in groundwater.

Methyl bromide (CH 3 Br) and methyl chloride (CH 3 Cl) significantly contribute to stratospheric ozone depletion. The atmospheric budgets of both compounds are unbalanced with known degradation processes outweighing known emissions. Stable isotope analysis may be capable to identify and quantify emissions and to achieve a balanced budget. Degradation processes do, however, cause isotope fractionation in methyl halides after emission and hence knowledge about these processes is a crucial prerequisite for any isotopic mass balance approach. In the current study, triple-element isotope analysis ( 2 H, 13 C, 37 Cl/ 81 Br) was applied to investigate the two main abiotic degradation processes of methyl halides (CH 3 X) in fresh and seawater: hydrolysis and halide exchange. For CH 3 Br, nucleophilic attack by both H 2 O and Cl - caused significant primary carbon and bromine isotope effects accompanied by a secondary inverse hydrogen isotope effect. For CH 3 Cl only nucleophilic substitution by H 2 O was observed at significant rates causing large primary carbon and chlorine isotope effects and a secondary inverse hydrogen isotope effect. Observed dual-element isotope ratios differed slightly from literature values for microbial degradation in water and hugely from radical reactions in the troposphere. This bodes well for successfully distinguishing and quantifying degradation processes in atmospheric methyl halides using triple-element isotope analysis.

Methyl bromide is the most important natural bromine contributor to stratospheric ozone depletion, yet there are still large uncertainties regarding quantification of its sources and sinks. The stable bromine isotope composition of CH(3)Br is potentially a powerful tool to apportion its sources and to study both its transport and its reactive fate. A novel compound-specific method to measure (81)Br/(79)Br isotope ratios in CH(3)Br using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry (GC/MCICPMS) was developed. Sample amounts of >40 ng could be measured with a precision of 0.1‰ (1σ, n = 3). The method results are reproducible over the long term as shown with 36 analyses acquired over 3 months, yielding a standard deviation (1σ) better than 0.4‰. This new method demonstrates for the first time Br isotope ratio determination in gaseous brominated samples. It is three orders of magnitude more sensitive than previously existing isotope ratio mass spectrometry methods for Br isotope determination of other organobromines, thus allowing applications towards ambient atmospheric samples., (Copyright © 2011 John Wiley & Sons, Ltd.)