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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]

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]

• We review Prof. Sherwood Lollar's contributions to Compound Specific Isotope Analysis. • We address contributions to contaminant hydrogeology and environmental chemistry. • We discuss contributions to fundamental science and to the remediation industry. Here, we review the contributions of Professor Barbara Sherwood Lollar to Compound Specific Isotope Analysis (CSIA) in contaminant hydrogeology and environmental chemistry. We first discuss the seminal work by Professor Sherwood Lollar's lab on establishing CSIA as a quantitative tool for contaminant (bio)transformation at contaminated groundwater sites. We describe the critical research by her lab in the development and validation of sample collection techniques, single- and multi-element CSIA, and isotope data evaluation for reliable interpretations. We highlight the contributions of Professor Sherwood Lollar's lab towards the development of best practices for the successful application of CSIA by industry to demonstrate the occurrence of (bio)transformation, identify (bio)transformation mechanisms, quantify the extent and rate of degradation and differentiate among potential contaminant sources. We then explore Professor Sherwood Lollar's applications of CSIA to hydrogeology of the deep subsurface and the fast widening of the field to new environments (e.g., sediments), contaminants (e.g., chlorofluorocarbons, pesticides), and systems (e.g., plant, enzymes). [ABSTRACT FROM AUTHOR]