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Stable bromine isotopic composition of methyl bromide: Method development and applications
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The isotopic composition of ozone depleting methyl halides may provide valuable information on the sources and sinks of these compounds. However, so far mostly stable carbon isotope analysis of methyl chloride and methyl bromide (CH3Br) has been attempted. Especially halogen isotope analysis has been hindered by the challenge to obtain sufficiently large amounts of methyl halides to meet the detection limits of existing isotope analytical methods. The purpose of this doctoral thesis was to develop both a high-volume cryogenic collection system for methyl bromide (Article II) and an analytical technique being able to analyze the sampled amounts of CH3Br for its Br isotopic composition, which was accomplished by using gas chromatography multiple-collector inductively-coupled plasma mass spectrometry (Article I). These methods were applied in the field campaign from which we report the first bromine isotopic values of CH3Br in the atmosphere (Article III), being in the range of -0.47 to + 1.75 ‰ vs. SMOB (Standard Mean Ocean Bromide). A laboratory study on pectin and halophyte plant material (Article IV) gave an insight in Br isotope composition of abiotically formed CH3Br which may be a main source to the atmospheric budget. These plant experiments yielded δ81Br values of 0 to -2 ‰ SMOB. Atmospheric CH3Br and this potential source showed partly distinct δ81Br ranges and demonstrate the potential of Br isotopes for source apportionment.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm University , 2013. , 26 p.
National Category
Earth and Related Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-89454ISBN: 978-91-7447-705-4 (print)OAI: oai:DiVA.org:su-89454DiVA: diva2:618032
Public defence
2013-06-04, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Submited. Paper 4: Manuscript.

Available from: 2013-05-13 Created: 2013-04-25 Last updated: 2017-11-23Bibliographically approved
List of papers
1. Compound-specific bromine isotope analysis of methyl bromide using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry
Open this publication in new window or tab >>Compound-specific bromine isotope analysis of methyl bromide using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry
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2011 (English)In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 25, no 17, 2425-2432 p.Article in journal (Refereed) Published
Abstract [en]

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 CH3Br using gas chromatography hyphenated with inductively coupled plasma multiple-collector mass spectrometry (GC/MCICPMS) was developed. Sample amounts of >40 ng could bemeasured with a precision of 0.1 parts per thousand (1 sigma, n=3). The method results are reproducible over the long term as shown with 36 analyses acquired over 3 months, yielding a standard deviation ( 1s) better than 0.4 parts per thousand. 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.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-66539 (URN)10.1002/rcm.5144 (DOI)000294267200008 ()
Note
authorCount :7Available from: 2011-12-27 Created: 2011-12-20 Last updated: 2017-12-08Bibliographically approved
2. A High-Volume Cryosampler and Sample Purification System for Bromine Isotope Studies of Methyl Bromide
Open this publication in new window or tab >>A High-Volume Cryosampler and Sample Purification System for Bromine Isotope Studies of Methyl Bromide
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2013 (English)In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 30, no 9, 2095-2107 p.Article in journal (Refereed) Published
Abstract [en]

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 Br-81-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 Br-81 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 Br-81-CH3Br of +0.03 parts per thousand +/- 0.10 parts per thousand relative to their starting composition. Finally, the combined cryosampler-purification and analysis system was applied to demonstrate the first-ever Br-81-CH3Br in the ambient atmosphere with two samples collected in the autumn of 2011, yielding -0.08 parts per thousand +/- 0.43 parts per thousand and +1.75 parts per thousand +/- 0.13 parts per thousand versus standard mean ocean bromide for samples collected at a suburban Stockholm, Sweden, site.

Keyword
Arctic, Europe, In situ atmospheric observations, Instrumentation, sensors, Isotopic analysis, Sampling
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-95775 (URN)10.1175/JTECH-D-12-00228.1 (DOI)000324890100010 ()
Note

AuthorCount:7;

Available from: 2013-11-04 Created: 2013-11-04 Last updated: 2017-12-06Bibliographically approved
3. Stable bromine isotopic composition of atmospheric CH3Br
Open this publication in new window or tab >>Stable bromine isotopic composition of atmospheric CH3Br
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(English)Article in journal (Refereed) Submitted
National Category
Natural Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-89402 (URN)
Available from: 2013-04-24 Created: 2013-04-24 Last updated: 2013-04-25Bibliographically approved
4. Stable bromine isotopic composition of methyl bromide released from plant matter
Open this publication in new window or tab >>Stable bromine isotopic composition of methyl bromide released from plant matter
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2014 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 125, 186-195 p.Article in journal (Refereed) Published
Abstract [en]

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 (delta Br-81) 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 (epsilon) of -2.00 +/- 0.23 parts per thousand (1 sigma, n = 8) for pectin and -1.82 +/- 0.02 parts per thousand (1 sigma, n = 4) for Salicornia (the relative amount of the heavier Br-81 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 degrees C. For longer incubations of up to 90 h at 180 degrees C the delta Br-81 values increased from -2 parts per thousand to 0 parts per thousand for pectin and to -1 parts per thousand for Salicornia. These delta Br-81 source signatures of CH3Br formation from plant matter combine with similar data for carbon isotopes to facilitate multidimensional isotope diagnostics of the CH3Br budget.

Keyword
bromine, isotope, plants, atmosphere, methyl bromide
National Category
Geochemistry Geophysics
Research subject
Applied Environmental Science; Environmental Chemistry
Identifiers
urn:nbn:se:su:diva-89403 (URN)10.1016/j.gca.2013.10.016 (DOI)000329066500012 ()
Available from: 2013-04-24 Created: 2013-04-24 Last updated: 2017-12-06Bibliographically approved

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