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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]

In the Müller-Rochow process or direct process, CH 3 Cl reacts with silicon, forming (CH 3) 2 SiCl 2 (M2) as the dominant species with copper as catalyst. This complex and highly heterogeneous process takes place in a gas-solid stirred fluidized bed reactor. In this study, the formation of (CH 3) 2 SiCl 2 on a Cu rich Cu-Si model has been investigated using density functional theory (DFT). The results show that the overall reaction is exoergic. Upon dissociation of CH 3 Cl, the reaction proceeds first by interaction of CH 3 with Si followed by subsequent addition of Cl. The largest activation barrier is found for the second Si-Cl bond formation in which a weakly adsorbed (CH 3) 2 SiCl 2 is formed. Compared to dehydrogenation of adsorbed CH 3 formed upon dissociation of CH 3 Cl, formation of M2 is energetically favoured on a Si modified Cu(111) model. [Display omitted] • A reaction path for ( CH 3 ) 2 SiCl 2 formation in the Müller-Rochow process is proposed. • The Müller-Rochow reaction can proceed on a Cu-rich mixed Cu-Si phase. • Coke precursor formation is more advantageous with Si in the Cu surface. • The path to ( CH 3 ) 2 SiCl 2 is advantageous compared to formation of coke precursors. [ABSTRACT FROM AUTHOR]

• The CH 3 Cl in flue gas can cause chloride corrosion on 12Cr1Mo alloy at 500, 600, and 700 °C. • The chlorine is enriched at defects of alloy surface during CH 3 Cl corrosion. • The thickness of oxide layer under CH 3 Cl atmosphere is larger than that of HCl. • The chlorine-rich bulges were observed in the alloy matrix under CH 3 Cl atmosphere. In biomass boilers, chlorine corrosion can be caused by various sources, including inorganic chlorine (HCl) and organic chlorine such as CH 3 Cl. This study utilized thermodynamic software, Factsage, to calculate the decomposition reaction of organic chlorine CH 3 Cl in an oxidizing atmosphere ranging from 500 to 700 °C. The results indicated the generation of HCl and Cl 2 components. With increasing temperature, the production rate of HCl increased while that of Cl 2 decreased. Meanwhile, the amount of HCl decomposition to produce Cl 2 also decreases with increasing temperature, but it remains higher than the yield of CH 3 Cl. The exposure behavior of 12Cr1MoV alloy was investigated under two chlorine sources at temperatures ranging from 500 to 700 °C. In the CH 3 Cl atmosphere, the alloy exhibited weight gains of approximately 0.6 %, 5.8 %, and 8.1 % at different temperatures, respectively. Whereas in the HCl atmosphere, the weight gains were approximately 0.1 %, 9.5 %, and 11.6 %, respectively. Corrosion products in the CH 3 Cl atmosphere at 500 and 600 °C were primarily composed of Fe 2 O 3 and FeCl 2. Increasing temperature accelerated the corrosion reaction. XRD analysis at 700 °C also identified corrosion products such as Cr 2 O 3 , (Fe, Cr) 3 O 4 , etc. Furthermore, the thickness of the oxide layer decreased with increasing temperature, leading to an increased gap with the substrate. At 600 °C in the CH 3 Cl atmosphere, the oxidation layer of the specimen consisted mainly of Fe 2 O 3 at the top and FeO and Fe 3 O 4 /Cr 3 O 4 at the bottom. With increasing temperature, the content of Cr 2 O 3 in the oxidation layer increased, and FeO transformed into the other two components. In the HCl atmosphere, the composition of the oxide layer in specimens at both temperatures remains consistent: Fe 2 O 3 /Cr 2 O 3 in the upper part and Fe 3 O 4 /Cr 3 O 4 in the lower part. Additionally, numerous chlorine-rich bubble structures were observed in the CH 3 Cl group specimens. These structures had an outer shell consisting of FeCl 2 and Fe 2 O 3 , while the inner filler comprised Fe 3 O 4 , Cr 3 O 4 , FeCl 2 , and CrCl 2. This phenomenon may be attributed to the denser corrosion products formed under the CH 3 Cl atmosphere, which led to greater obstruction of metal chloride diffusion compared to the HCl atmosphere, resulting in the accumulation of metal chlorides on the substrate. [ABSTRACT FROM AUTHOR]

Methyl Chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. While the atmospheric CH3Cl emissions are predominantly caused by natural sources on the global budget, significant uncertainties still remain for the anthropogenic CH3Cl emission strengths. In summer 2007 an intensive field campaign within the ACTRIS-2 Project was hosted at the Mt. Cimone World Meteorological Organization/Global Atmosphere Watch global station (CMN, 44,17° N, 10,68° E, 2165 m a.s.l.). High-frequency and high precision in situ measurements of atmospheric CH3Cl revealed significant high-frequency variability superimposed on the seasonally varying regional background levels. The high-frequency CH3Cl variability was characterized by an evident cycle over 24 h with maxima during the afternoon which points towards a systematic role of thermal vertical transport of air-masses from the regional boundary layer. The temporal correlation analysis with specific tracers of anthropogenic activity (traffic, industry, petrochemical industry) together with bivariate analysis as a function of local wind regime suggested that, even if the role of natural marine emissions appears as predominant, the northern Italy boundary layer could potentially represent a non-negligible source of CH3Cl during summer. Since industrial production and use of CH3Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of CH3Cl outflow from the Po Basin is important to properly assess its anthropogenic emissions.

Abstract: Rotational transitions in CH3 35Cl mixed with CO2 are recorded at 296K and total pressures up to 0.6Torr in the frequency interval 186–901GHz (1.6–0.3mm) for J=6→7, 10→11, 17→18, 22→23, 31→32, 33→34 and K=0–6, using the frequency-modulation spectrometer of the Laboratory PhLAM (Lille, France). These line-shapes are analyzed with the commonly used Voigt profile as well as with more refined Speed-Dependent Voigt and Galatry models accounting for the line narrowing induced, respectively, by the speed-dependence of the relaxation parameters and by velocity-changing collisions. Due to the high line intensities, the fitting procedure involves the full implementation of the Beer–Lambert law instead of its traditional linear approximation. The experimentally deduced J- and K-dependences of the pressure-broadening coefficients are further used to obtain the model parameters of a semi-empirical approach allowing massive calculations of line-shape parameters for enlarged ranges of rotational quantum numbers requested by spectroscopic databases. [Copyright &y& Elsevier]

Abstract: Relaxation parameters for K-components (K≤6) of six J→J+1 rotational transitions (J=6, 10, 17, 22, 31 and 33) of CH3 35Cl perturbed by O2 are measured at room temperature with Voigt, speed-dependent Voigt and Galatry profiles in order to probe the speed-dependence effects. With respect to the previous study of CH3 35Cl–N2 system [Guinet et al., J Quant Spectrosc Radiat Transfer 2012;113:1113], higher active-gas pressures are reached, providing better signal-to-noise ratios, and the exact expression of the Beer–Lambert law is introduced in the fitting procedure, leading, among other advantages, to much more realistic low-pressure results. The broadening parameters of the considered lines are also computed by a semi-classical method for various relative velocities of colliders and the powers characterizing the dependence of the collisional cross-sections on relative speeds are deduced as functions of the rotational numbers J and K. Additional calculations performed with the Maxwell–Boltzmann distribution of velocities show no significant difference with the earlier results [Buldyreva et al., Phys Chem Chem Phys 2011;13:20326] obtained within the mean thermal velocity approximation. Weighted sums of the presently measured Voigt-profile O2-broadening parameters and of the previously published N2-broadening ones are calculated to yield experimental air-broadening coefficients for spectroscopic databases. [Copyright &y& Elsevier]

Hydrogen-broadening coefficients of methyl chloride rotational lines J = 6 → 7, 10 → 11, 17 → 18, 22 → 23 and 31 → 32 at 296 K are measured as functions of the quantum number K using a sensitive frequency-modulation technique. As expected for this light perturber, the observed line shapes are well described by Voigt profile model. A clear dependence of the collisional broadening on K is observed for most transitions. From a detailed study of the K-components of the transition J = 6 → 7 situated at 186 GHz no variation of the broadening of the hyperfine components related to 35Cl quadrupole is stated. Given the absence of refined ab initio computed potential energy surfaces and the impracticality of quantum-mechanical calculations for the considered molecular system, theoretical values of these broadening coefficients are estimated by a semi-classical approach with exact trajectories and a model interaction potential including both long-range and short-range (atom-atom) interactions of the active molecule rigorously treated as a symmetric top. It is shown that the short-range forces yield important contributions to the collisional line width for all values of the rotational quantum numbers J and K. Various models are also tested for the isotropic part of the interaction potential which governs the relative translational motion. It is demonstrated that for the very light perturbing molecule H2 the calculated line widths, practically independent from the rotational quantum number J (for K ≤ J), are particularly sensitive to the position and slope of the repulsive wall. Modifications required in the semi-classical formalism for a correct application of the cumulant expansion are also tested and it is stated that no difference is observed for the CH3Cl–H2 system characterised by quite weak interactions. [ABSTRACT FROM PUBLISHER]

Abstract: Room-temperature N2-broadening coefficients of methyl chloride rotational lines are measured over a large interval of quantum numbers (6≤J≤50, 0≤K≤18) by a submillimeter frequency-multiplication chain (J≤31) and a terahertz photomixing continuous-wave spectrometer (J≥31). In order to check the accuracy of both techniques, the measurements of identical lines are compared for J=31. The pressure broadening coefficients are deduced from line fits using mainly a Voigt profile model. The excellent signal-to-noise ratio of the frequency-multiplication scheme highlights some speed dependence effect on the line shape. Theoretical values of these coefficients are calculated by a semi-classical approach with exact trajectories. An intermolecular potential including atom–atom interactions is used for the first time. It is shown that, contrary to the previous theoretical predictions, the contributions of short-range forces are important for all values of the rotational quantum numbers. Additional testing of modifications required in the semi-classical formalism for a correct application of the cumulant expansion is also performed. It is stated that the use of the cumulant average on the rotational states of the perturbing molecule leads, for high J and small K values, to slightly higher line-broadening coefficients, as expected for the relatively strong interacting CH3Cl–N2 system. The excellent agreement between the theoretical and the experimental results ensures the reliability of these data. [Copyright &y& Elsevier]

The recently presented ab initio calculations for the reaction system of CH3Cl + OH (Dehestani and Shojaie, Int J Quantum Chem, in press) are applied to the vibrational mode analysis. Extending previous work, we use the vibrational mode analysis to elucidate the relationships of the reactants, the transition state, the intermediates (IM), and the products. The extensive investigation shows that the reaction mechanism is reliable. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

Abstract: Methyl chloride (CH3Cl) is one of the most abundant chlorine-containing molecules in the atmosphere. For this reason a recent update was performed in HITRAN in the 640–2600cm−1 region based on the line parameters generated in Nikitin et al. [Nikitin A, Champion JP, Bürger H. J Mol Spectrosc 2005;230:174–84] with the intensities scaled to existing experimental data. CH3Cl has a rather strong signature around 3000cm−1 which was used recently by the Atmospheric Chemistry Experiment (ACE) satellite mission to produce the first study of the global distribution of methyl chloride in the upper troposphere and stratosphere. However, it was mentioned that the CH3Cl line positions and intensities spectroscopic parameters are of very low quality in this spectral region in the public access HITRAN or GEISA databases. We present a complete update of the line positions and line intensities for the ν 1, ν 4, 3ν 6 bands of CH3 35Cl and CH3 37Cl in the 3.4μm region. For this task, Fourier transform spectra have been recorded at high resolution at the Laboratoire de Dynamique, Interactions et Réactivité in France. Measurements of line positions and line intensities have been retrieved for both isotopologues 12CH3 35Cl and 12CH3 37Cl in the ν 1, ν 4, 3ν 6 bands. The theoretical model accounts for the interactions coupling the (ν 1=1; ℓ=0), (ν 4=1; ℓ=±1) and (ν 6=3; ℓ=±1) energy levels, together with additional resonances involving several dark states. [Copyright &y& Elsevier]

Abstract: In conjunction with the OP3 campaign in Danum Valley, Malaysian Borneo, flux measurements of methyl chloride (CH3Cl) and methyl bromide (CH3Br) were performed from both tropical plant branches and leaf litter in June and July 2008. Live plants were mainly from the Dipterocarpaceae family whilst leaf litter samples were representative mixtures of different plant species. Environmental parameters, including photosynthetically-active radiation, total solar radiation and air temperature, were also recorded. The dominant factor determining magnitude of methyl halide fluxes from living plants was plant species, with specimens of the genus Shorea showing persistent high emissions of both gases, e.g. Shorea pilosa: 65 ± 17 ng CH3Cl h−1 g−1 (dry weight foliage) and 2.7 ± 0.6 ng CH3Br h−1 g−1 (dry weight foliage). Mean CH3Cl and CH3Br emissions across 18 species of plant were 19 (range,

Abstract: Potential energy curves have been calculated for the dissociation of the neutral CH3Cl molecule and its negative ion into CH3 +Cl and , respectively. The neutral molecule and the anion could be treated by means of standard wave function based quantum chemical ab initio methods for C–Cl distances larger than about 2.4Å, where is a stable anion. In the present calculation MP3 and CCSD(T) were employed. At shorter C–Cl distances the anion is only metastable and cannot be treated by such methods. We have applied a stabilization scheme, first proposed by Nestmann and Peyerimhoff, to stabilize the metastable anion by adding extra positive charges to the molecule. By this trick it was possible to generate the resonance energy E res and width Γ as functions of the C–Cl distance in the resonance regime between 1.5 and 2.5Å. The calculated values for the threshold energy E thresh and the exothermicity ΔE 0 of the DEA (dissociative electron attachment) process are in very good agreement with experiment; the vertical attachment energy (VAE) is smaller than its experimental counterpart. [Copyright &y& Elsevier]

A survey of methyl chloride (CH3Cl)-emitting plants was performed at a subtropical island in Japan (Iriomote Island). Among the 187 species of tropical/subtropical plants investigated, 33 species from a variety of families were identified as CH3Cl-emitting plants. The strongest emitters were Osmunda banksiifolia, Cibotium balometz, Angiopteris palmiformis, Vitex rotundifolia, Vitex trifolia, and Excoecaria agalloch, each with CH3Cl emission rates exceeding 1μg (gdrywt)−1 h−1. The first three species are ferns, and the last three are halophilous plants. Based on our results, the character of CH3Cl emission is likely to be shared at the genus level but not always at the family level. The atmospheric CH3Cl distribution measured on Iriomote Island showed significant enhancement in forested sites (up to 2750ppt) and a higher concentration on the downwind shore than on the upwind shore. As previously reported, our findings provide strong evidence for the high emission of CH3Cl from tropical/subtropical forests. [Copyright &y& Elsevier]

Abstract: A new step for complete experiments in photoionization (PI) of linear molecules is achieved when the electron-ion vector correlation method, based on imaging and time-of-flight resolved electron-ion coincidence techniques, is combined with the use of elliptically polarized light. The molecular frame photoelectron angular distributions (MFPADs), as well as the s 1 and s 2 Stokes parameters characterizing the polarization state of the light, can be derived from a single experiment performed with undefined elliptically polarized light. Using this method, we report and discuss MFPADs for site selective K-shell ionization of the NO and N2O linear molecules in the region of the N 1s and O 1s shape resonances. A large molecular frame circular dichroism is observed, well predicted by the multi-channel Schwinger configuration interaction calculations reported for PI of NO. We also present recent experimental results for PI of non-linear molecules like CH3Cl measured above the Cl 2p and C 1s ionization thresholds: the recoil frame photoelectron angular distributions (RFPADs) obtained by the vector correlation method may be influenced both by the molecular frame photoemission pattern and the fragmentation process. [Copyright &y& Elsevier]

Abstract: High-resolution photoabsorption spectra of CH3Cl and CH3I are reported in the energy range 3.9–10.8eV (320–115nm). Several features are observed for the first time in the CH3Cl spectrum and a number of new assignments are proposed. For both molecules, the present work provides the most reliable absolute cross-sections yet reported at energies above the dissociative A band transition. [Copyright &y& Elsevier]

Abstract: Extensive experiments on the K=5 component of the J=14–13 rotational transition of CH3 35Cl, located near 372GHz, were performed at different temperatures in the range 235–350K. They allow the determination of the N2- and O2-broadening coefficients, and their temperature dependences. More specific measurements on a great number of K-components of the involved transition perturbed by N2 at 301K allow to point out a clear decreasing of the broadening coefficients with increasing K. All the experimental parameters are compared with results derived from a semiclassical calculation of collisional interactions, including electrostatic, induction, and dispersion energy contributions. [Copyright &y& Elsevier]

Smoke from wood burning is a significant source of air pollution in many parts of the world. When several sources simultaneously cause air pollution, it is often difficult to determine how much comes from wood burning. Wood smoke has unique chemical characteristics that can be used as indicators, including elemental composition, particularly potassium and chlorine, the ratios of organic and elemental carbon, and gases such as methyl chloride. This paper deals with formulating and applying the chemical mass balance approach incorporating both gas- and aerosol-phase tracers to a study carried out at Olympia-Lacey in Washington. In this study, three types of tracers were measured simultaneously and used to estimate wood smoke pollution during Winter, namely elemental composition and organic carbon in the particle phase and methyl chloride in the gas phase. The results from the different tracers are found to be in agreement. The air pollution at the study site was dominated by wood smoke mostly from low-temperature combustion (about 80%), with additional but smaller contributions from oil furnaces (15%), automobiles (4%) and occasionally from other nearby sources. [Copyright &y& Elsevier]

The spatial and temporal distribution of atmospheric chloromethane (CH 3 Cl) in China was investigated between 2012 and 2014, and the sources of CH 3 Cl were evaluated by positive matrix factorization (PMF) according to PMF 5.0 (USEPA). Various concentrations of CH 3 Cl were found throughout China, ranging from 506.4 ± 110.5 to 1132.1 ± 523.3 pptv, showing the characteristics of high in the southeast and low in the northwest. The correlation between CH 3 Cl and chlorofluorocarbon-12 (CFC-12) at most sites was greater than 0.5 and presented regional characteristics. The distribution of CH 3 Cl in China is related to the degree of economic development, the high-concentration sites were located in the economically developed eastern region. The CH 3 Cl concentrations at western sites were similar to the global average and increased with latitude and altitude, indicating that this region was least affected by anthropogenic activities. The annual average concentrations of atmospheric CH 3 Cl in the northeastern region were below 730 pptv but had strong seasonal fluctuations. Chemical production was the main CH 3 Cl source in the northeast background areas (46%), while industrial combustion contributed 42% of the CH 3 Cl in the northeast urban areas. Large seasonal variations combined with a high relative standard deviation were observed in the southern region. Relative to the southwest, in the southeast, the onset of lower concentrations was delayed until September–October, and higher concentrations persisted for longer. Chemical production and biomass burning were the main sources in the southwest, while Chemical production and solvent use were the main contributors in the southeast. The Beijing area is discussed separately as a super megacity. No obvious seasonal fluctuations were observed in the Beijing area. According to the source analysis, chemical production contributed approximately 60% of the atmospheric CH 3 Cl in the Beijing area, while 15–24% was from solvent release. • High concentrations of CH 3 Cl are concentrated in the central and eastern regions in China. • Chemical production is the main source of atmospheric CH 3 Cl in China. • Industrial combustion is the second source of the CH 3 Cl in the northeast. • Biomass burning and solvent use are important CH 3 Cl contributors in the southern region. [ABSTRACT FROM AUTHOR]

Methyl Chloride (CH3Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. While the atmospheric CH3Cl emissions are predominantly caused by natural sources on the global budget, significant uncertainties still remain for the anthropogenic CH3Cl emission strengths. In summer 2007 an intensive field campaign within the ACTRIS-2 Project was hosted at the Mt. Cimone World Meteorological Organization/Global Atmosphere Watch global station (CMN, 44.17° N, 10.68° E, 2165 m a.s.l.). High-frequency and high precision in situ measurements of atmospheric CH3Cl revealed significant high-frequency variability superimposed on the seasonally varying regional background levels. The high-frequency CH3Cl variability was characterized by an evident cycle over 24 h with maxima during the afternoon which points towards a systematic role of thermal vertical transport of air-masses from the regional boundary layer. The temporal correlation analysis with specific tracers of anthropogenic activity (traffic, industry, petrochemical industry) together with bivariate analysis as a function of local wind regime suggested that, even if the role of natural marine emissions appears as predominant, the northern Italy boundary layer could potentially represent a non-negligible source of CH3Cl during summer. Since industrial production and use of CH3Cl have not been regulated under the Montreal Protocol (MP) or its successor amendments, continuous monitoring of CH3Cl outflow from the Po Basin is important to properly assess its anthropogenic emissions. [ABSTRACT FROM AUTHOR]

Ab initio computational study of the electronic structure and infrared spectra of donor–acceptor complexes formed between SO3 and CH3X (X = F, Cl, Br) molecules was carried out at the MP2(full)/6–31G(d) level of theory. The calculated complexation energy at G2MP2 level shows that stability of complexes decrease, as CH3Cl&z.sbnd;SO3 > CH3Br&z.sbnd;SO3 > CH3F&z.sbnd;SO3. The NBO partitioning scheme show that the lengthening of the C&z.sbnd;F, C&z.sbnd;Cl, and C&z.sbnd;Br bond lengths, upon complexation, is due to an decreasing “s” character in these bonds. [Copyright &y& Elsevier]