Methyl Chloride Emissions Research Articles

Long-term high frequency measurements of ethane, benzene and methyl chloride at Ragged Point, Barbados: Identification of long-range transport events

Abstract Here we present high frequency long-term observations of ethane, benzene and methyl chloride from the AGAGE Ragged Point, Barbados, monitoring station made using a custom built GC-MS system. Our analysis focuses on the first three years of data (2005–2007) and on the interpretation of periodic episodes of high concentrations of these compounds. We focus specifically on an exemplar episode during September 2007 to assess if these measurements are impacted by long-range transport of biomass burning and biogenic emissions. We use the Lagrangian Particle Dispersion model, NAME, run forwards and backwards in time to identify transport of air masses from the North East of Brazil during these events. To assess whether biomass burning was the cause we used hot spots detected using the MODIS instrument to act as point sources for simulating the release of biomass burning plumes. Excellent agreement for the arrival time of the simulated biomass burning plumes and the observations of enhancements in the trace gases indicates that biomass burning strongly influenced these measurements. These modelling data were then used to determine the emissions required to match the observations and compared with bottom up estimates based on burnt area and literature emission factors. Good agreement was found between the two techniques highlight the important role of biomass burning. The modelling constrained by in situ observations suggests that the emission factors were representative of their known upper limits, with the in situ data suggesting slightly greater emissions of ethane than the literature emission factors account for. Further analysis was performed concluding only a small role for biogenic emissions of methyl chloride from South America impacting measurements at Ragged Point. These results highlight the importance of long-term high frequency measurements of NMHC and ODS and highlight how these data can be used to determine sources of emissions 1000’s km away.

Methyl chloride emissions from halophyte leaf litter: Dependence on temperature and chloride content

Methyl chloride (CH3Cl) is the most abundant natural chlorine containing compound in the atmosphere, and responsible for a significant fraction of stratospheric ozone destruction. Understanding the global CH3Cl budget is therefore of great importance. However, the strength of the individual sources and sinks is still uncertain. Leaf litter is a potentially important source of methyl chloride, but factors controlling the emissions are unclear. This study investigated CH3Cl emissions from leaf litter of twelve halophyte species. The emissions were not due to biological activity, and emission rates varied between halophyte species up to two orders of magnitude. For all species, the CH3Cl emission rates increased with temperature following the Arrhenius relation. Activation energies were similar for all investigated plant species, indicating that even though emissions vary largely between plant species, their response to changing temperatures is similar. The chloride and methoxyl group contents of the leaf litter samples were determined, but those parameters were not significantly correlated to the CH3Cl emission rate.

Methyl chloride and C2–C5 hydrocarbon emissions from dry leaf litter and their dependence on temperature

Emissions of methyl chloride and several C2–C5 hydrocarbons from dry leaf litter at temperatures in the range 20–100 °C are reported for different plant species. The emission rates of ethane, ethene, propane, propene, n-pentane and methyl chloride increased with temperature. Hydrocarbon emission rates up to 0.88 ng gdw−1 h−1 were measured at 20 °C, while methyl chloride emission rates between 0.03 and 0.85 ng gdw−1 h−1 were observed at this temperature. At 70 °C emission rates increased up to 650 ng gdw−1 h−1 for C2–C5 hydrocarbons and up to 18 μg gdw−1 h−1 for methyl chloride. The Arrhenius relation can be used to describe the temperature dependence of methyl chloride emissions, while for hydrocarbon emissions deviations from this relation were observed. The emissions were not due to enzymatic activity, which was indicated by emission rates that continuously increased with increasing temperature, and activation energies higher than 50 kJ mol−1. At constant temperature, the emission rate of both methyl chloride and hydrocarbons from dry leaf litter decreased in time. At high temperatures (80–100 °C) this was noticeable on a timescale of hours, while at low temperatures (20–30 °C) the decrease was very slow and only visible on a timescale of months. Emission of methyl chloride from leaf litter might be significant for its global budget, while temperature induced hydrocarbon emissions from leaf litter are likely insignificant.

Identification of coastal emissions of methyl chloride and methyl bromide based on high-frequency measurements on Hateruma Island

Hourly measurements of atmospheric methyl chloride (CH3Cl) and methyl bromide (CH3Br), as well as some other halocarbons, were performed by using automated preconcentration gas chromatography/mass spectrometry at Hateruma Island, the southernmost inhabited island in the Japanese archipelago. Our data indicate that CH3Cl and CH3Br concentrations were occasionally increased without corresponding increases of anthropogenic halocarbons, such as HCFC-22. Those nonpollution high-CH3Cl and high-CH3Br events were observed mostly when the wind was blowing at rather low speed along the shore (a partially vegetated raised coral beach). Presuming that these methyl halides were accumulated while the air mass traveled over the beach, the emission strengths of CH3Cl and CH3Br from the beach were roughly estimated to be 900 ± 350 μg m-2h-1 and 21 ± 10 μg m-2h-1, respectively. Coastal beach is likely a new important source for CH3Cl and CH3Br on a global scale.

Fast determination of methyl chloride and methyl bromide emissions from dried plant matter and soil samples using HS-SPME and GC-MS: method and first results

Environmental context. Headspace solid-phase microextraction (HS-SPME) and analysis by gas chromatography–mass spectrometry (GC/MS) system has been employed for quantifying the emissions of methyl chloride (CH3Cl) and methyl bromide (CH3Br) from plants and soils. Compared with more commonly used techniques, HS-SPME coupled to GC/MS is simple, fast, sensitive, economical and non-destructive, with potential for laboratory-based and field studies. Abstract. Headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC/MS) system have been employed for quantifying the emissions of methyl chloride (CH3Cl) and methyl bromide (CH3Br) from plants and soils. Seven SPME fibre coatings including 75 μm Carboxen-polydimethylsiloxane (CAR-PDMS), 85 μm Carboxen-PDMS (CAR-PDMS), 50/30 μm divinylbenzene-CAR-PDMS (DVB-CAR-PDMS), 65 μm DVB-PDMS, 65 μm carbowax-DVB (CW-DVB), 30 μm PDMS (PDMS) and 100 μm PDMS, were tested by comparing their sampling efficiencies towards CH3Cl and CH3Br. Key parameters such as extraction time, desorption temperature and time were all optimised in this work. The optimum conditions were found with CAR-PDMS 75 μm as an SPME fibre coating, a 1-min sampling time, a 50°C incubation temperature and a 2-min desorption time and a 250°C desorption temperature. These conditions were used for the determination of CH3Cl and CH3Br emission rates from different plant species as well as soil samples. Compared with more commonly used techniques, HS-SPME coupled to GC/MS is simple, fast, sensitive, economical and non-destructive, with potential for laboratory-based and field studies.

Characterization of three halide methyltransferases in Arabidopsis thaliana

Methyl chloride and methyl bromide, which contribute to the destruction of the stratospheric ozone layer, are mainly emitted from natural sources. It was recently reported that tropical and subtropical plants were the largest sources of methyl chloride. Furthermore, the involvement of the gene HARMLESS TO OZONE LAYER (HOL) in methyl halide emissions from Arabidopsis thaliana was demonstrated. However, neither the physiological significance of the methyl chloride emission nor the biochemical properties of HOL, denoted as AtHOL1 in our study, have been reported yet. We identified two additional isoforms-AtHOL2 and AtHOL3-from Arabidopsis and characterized them together with AtHOL1. AtHOL1 was ubiquitously expressed during development, and its expression level was the highest among the three. The phylogenetic tree suggested that AtHOL1 homologous proteins were distributed throughout the plant kingdom. Biochemical analyses showed that the three recombinant AtHOL proteins were functional and had distinct levels of the S-adenosyl-L- methionine-dependent methyltransferase activities. Although a study of AtHOL1-disrupted mutants had shown that AtHOL1 primarily controlled the production of methyl halide, our study suggested that the activation of AtHOL2 and AtHOL3 genes also contribute to the methyl halide emissions from Arabidopsis.

Ectomycorrhizal fungi: A new source of atmospheric methyl halides?

AbstractIncomplete source budgets for methyl halides – compounds that release inorganic chlorine and bromine radicals which, in turn, catalyze atmospheric ozone depletion – limit our ability to predict the fate of the stratospheric ozone layer. We report here the first measured emissions of methyl chloride, methyl bromide, and methyl iodide from ectomycorrhizal fungi. We grew nine fungal isolates on growth media containing halide concentrations similar to those found in soils and plant tissues. The observed range of emissions was 0.003–65 μg methyl chloride, 0.001–3 μg methyl bromide, and 0.02–12 μg methyl iodide g−1 dry weight fungi day−1. Species varied in production rates of methyl chloride vs. methyl bromide vs. methyl iodide. Cenococcum geophilum, a widespread ectomycorrhizal fungus, was further tested to investigate the effects of halide substrate concentration in growth media. Emissions from this species increased linearly with increasing concentrations of both bromide and iodide. In addition, a subset of four fungi was studied with two media concentrations each of chloride, bromide, and iodide (0.2 or 20 mm). These fungi had similar responses to halide concentration, despite 1000‐fold differences in baseline emission rates between isolates. Finally, high chloride concentrations (20 mm) in media did not appear to inhibit emissions of methyl bromide or methyl iodide. Overall, ectomycorrhizal fungi might be an important source of methyl halides to the atmosphere, and substrate concentrations and community composition may influence production levels in ecosystems.

A pilot study of methyl chloride emissions from tropical woodrot fungi

Flux chamber measurements made in a rainforest provide evidence that methyl chloride is emitted from rotting wood. However, its net flux was found to be into the soil, probably due to competing production and consumption processes within the soil. Evidence was found for a regional source, possibly vegetation, since its concentration above the canopy was substantially greater than reported average equatorial values.

Environmental controls over methyl halide emissions from rice paddies

This paper examines primary controlling factors that affect methyl halide emissions from rice paddy ecosystems. Observations of four cultivars under multiple growth conditions during studies in commercial fields and the University of California, Irvine, greenhouse lead to the conclusion that daily emissions of methyl halides are primarily determined by the growth stage of the rice plant, with the exception that methyl chloride emissions show no clear seasonal pattern. Methyl chloride emissions appear to be more from the paddy water and/or soil as opposed to the plants; however, in soils with high chloride content, these emissions appear to peak during the reproductive phase. Strong secondary influences include air temperature, soil halide concentration, and soil pore water saturation. The cultivars studied had statistically separate seasonally integrated emissions. Irradiant light and aboveground biomass appear to have little effect on emissions. Emissions of methyl chloride, methyl bromide, and methyl iodide are estimated to be 3.5, 2.3, and 48 mg/m2/yr, or 5.3, 3.5, and 72 Gg/yr, from rice paddies globally.

Interfield and intrafield variability of methyl halide emissions from rice paddies

Methyl halide gases are important sources of atmospheric inorganic halogen radicals. We measured methyl halide emissions from three rice fields over two full growing seasons. Rice paddy emissions of methyl chloride, methyl bromide and methyl iodide are insignificant until field flooding. Rice growth stage determines methyl bromide and methyl iodide emissions while methyl chloride emissions are comparable between planted and unplanted plots. Houston, Texas, and Maxwell, California, field integrated seasonal fluxes of methyl chloride, methyl bromide and methyl iodide are consistent (values range from 2.3 to 3.9, 0.8 to 1.1, and 28.1 to 62.0 mg m−2, respectively) despite differences in multiple field parameters. We also examined field emission variability using 12 chamber placements. Methyl bromide and methyl iodide emissions within homogenous rice paddies require at least three replicates to determine field mean fluxes within 20%, and for methyl chloride emissions, over 10 replications per field are necessary.

Strong emission of methyl chloride from tropical plants

Methyl chloride is the largest natural source of ozone-depleting chlorine compounds, and accounts for about 15 per cent of the present atmospheric chlorine content. This contribution was likely to have been relatively greater in pre-industrial times, when additional anthropogenic sources-such as chlorofluorocarbons-were absent. Although it has been shown that there are large emissions of methyl chloride from coastal lands in the tropics, there remains a substantial shortfall in the overall methyl chloride budget. Here we present observations of large emissions of methyl chloride from some common tropical plants (certain types of ferns and Dipterocarpaceae), ranging from 0.1 to 3.7 microg per gram of dry leaf per hour. On the basis of these preliminary measurements, the methyl chloride flux from Dipterocarpaceae in southeast Asia alone is estimated at 0.91 Tg yr-1, which could explain a large portion of missing methyl chloride sources. With continuing tropical deforestation, natural sources of chlorine compounds may accordingly decrease in the future. Conversely, the abundance of massive ferns in the Carboniferous period may have created an atmosphere rich in methyl chloride.

Isotopic Composition of Non-Methane Hydrocarbons in Emissions from Biomass Burning

The stable carbon isotope ratios of nonmethane hydrocarbons (NMHC) and methyl chloride emitted from biomass burning were determined by analyzing seven whole air samples collected during different phases of the burning process as part of a laboratory study of wood burning. The average of the stable carbon isotope ratios of emitted alkanes, alkenes and aromatic compounds is identical to that of the burnt fuel; more than 50% of the values are within a range of ±1.5‰ of thecomposition of the burnt fuel wood. Thus for the majority of NMHC emitted from biomass burning stable carbon isotope ratio of the burnt fuel a good first order approximation for the isotopic composition of the emissions. Of the more than twenty compounds we studied, only methyl chloride and ethyne differed in stable carbon isotope ratios by more than a few per mil from the composition of the fuel. Ethyne is enriched in 13C by approximately 20–30‰, and most of the variability can beexplained by a dependence on flame temperature. The δ 13C values decreaseby 0.019 ‰/K (±0.0053‰/K) with increasing temperature. Methyl chloride is highly depleted in 13C, on average by25‰. However the results cover a wide range of nearly 30‰. Specifically, in two measurements with wood from Eucalyptus (Eucalyptus delegatensis) as fuel we observed the emission of extremely light methyl chloride (–68.5‰and–65.5‰). This coincides with higher than average emission ratiosfor methyl chloride (15.5 × 10−5 and 18 ×10−5 mol CH3Cl/mol CO2). These high emission ratios are consistent with the highchlorine content of the burnt fuel, although, due to the limited number of measurements, it would be premature to generalize these findings. The limited number of observations also prevents any conclusion on a systematic dependence between chlorine content of the fuel, emission ratios and stable carbon isotope ratio of methyl chloride emissions. However, our results show that a detailed understanding of the emissions of methyl chloride from chloride rich fuels is important for understanding its global budget. It is also evident that the usefulness of stable carbon isotope ratios to constrain the global budget of methyl chloride will be complicated by the very large variability of the stable carbon isotope ratio of biomass burning emissions. Nevertheless, ultimately the large fractionation may provide additional constraints for the contribution of biomass burning emissions to the atmospheric budget of methyl chloride.

Emissions of methyl halides and methane from rice paddies.

Methyl halide gases are important sources of atmospheric inorganic halogen compounds, which in turn are central reactants in many stratospheric and tropospheric chemical processes. By observing emissions of methyl chloride, methyl bromide, and methyl iodide from flooded California rice fields, we estimate the impact of rice agriculture on the atmospheric budgets of these gases. Factors influencing methyl halide emissions are stage of rice growth, soil organic content, halide concentrations, and field-water management. Extrapolating our data implies that about 1 percent of atmospheric methyl bromide and 5 percent of methyl iodide arise from rice fields worldwide. Unplanted flooded fields emit as much methyl chloride as planted, flooded rice fields.

Natural methyl bromide and methyl chloride emissions from coastal salt marshes.

Atmospheric methyl bromide (CH3Br) and methyl chloride (CH3Cl), compounds that are involved in stratospheric ozone depletion, originate from both natural and anthropogenic sources. Current estimates of CH3Br and CH3Cl emissions from oceanic sources, terrestrial plants and fungi, biomass burning and anthropogenic inputs do not balance their losses owing to oxidation by hydroxyl radicals, oceanic degradation, and consumption in soils, suggesting that additional natural terrestrial sources may be important. Here we show that CH3Br and CH3Cl are released to the atmosphere from all vegetation zones of two coastal salt marshes. We see very large fluxes of CH3Br and CH3Cl per unit area: up to 42 and 570 micromol m(-2) d(-1), respectively. The fluxes show large diurnal, seasonal and spatial variabilities, but there is a strong correlation between the fluxes of CH3Br and those of CH3Cl, with an average molar flux ratio of roughly 1:20. If our measurements are typical of salt marshes globally, they suggest that such ecosystems, even though they constitute less than 0.1% of the global surface area, may produce roughly 10% of the total fluxes of atmospheric CH3Br and CH3Cl.

Atmospheric methyl halides and dimethyl sulfide from cattle

We have measured emissions of CH3Cl, CH3Br, and (CH3)2S (DMS) from Holstein cows. In one experiment, two cows were studied in separate metabolic research chambers for a 24‐hour period while on a normal diet and were studied for an additional 24‐hour period 1 week later after being placed on a diet enhanced in chloride and bromide. Methyl chloride emissions ranged between 0.4 × 10−3 and 1.5 × 10−3 g cow−1 d−1, while methyl bromide emissions were much smaller, 3 × 10−6−2 × 10−5 g cow−1 d−1. Daily emissions of methane from these cows were 134–180 g cow−1 d−1, quite similar to values found in many previous studies. A second 24‐hour study of two different cows on normal diets yielded daily emissions of 0.6 × 10−3 and 0.9 × 10−3 g CH3Cl, 0−1.0 × 10−6 g CH3Br, and 191 and 176 g CH4. If these emissions of CH3Cl and CH3Br are representative of the 1.3 billion head of cattle worldwide, then the global source of atmospheric CH3Cl and CH3Br from cattle would be 0.23–0.70 Gg yr−1 and (1–10) × 10−3 Gg yr−1, respectively. These emissions of CH3Cl and CH3Br represent <0.02% and <0.005%, respectively, of the total annual global atmospheric sources of these compounds; therefore, emissions of CH3Cl and CH3Br from cattle are insignificant contributors to their total sources. Discovered serendipitously, DMS emissions were between 0.17 and 0.24 g cow−1 d−1, and chloroform emissions were 2 × 10−4−3 × 10−3 g cow−1 d−1. DMS from cattle is not a major source over hemispheric or global scales but could be important in certain geographical regions. Chloroform (CHCl3) emissions were similarly detected and quantified, as were those of C2H5X (X = Cl or Br).

Natural emissions of chlorine‐containing gases: Reactive Chlorine Emissions Inventory

Although there are many chlorine‐containing trace gases in the atmosphere, only those with atmospheric lifetimes of 2 years or fewer appear to have significant natural sources. The most abundant of these gases are methyl chloride, chloroform, dichloromethane, perchloroethylene, and trichloroethylene. Methyl chloride represents about 540 parts per trillion by volume (pptv) Cl, while the others together amount to about 120 pptv Cl. For methyl chloride and chloroform, both oceanic and land‐based natural emissions have been identified. For the other gases, there is evidence of oceanic emissions, but the roles of the soils and land are not known and have not been studied. The global annual emission rates from the oceans are estimated to be 460 Gg Cl/yr for CH3Cl, 320 Gg Cl/yr for CHCl3, 160 Gg Cl/yr for CH2Cl2, and about 20 Gg Cl/yr for each of C2HCl3, and C2Cl4. Land‐based emissions are estimated to be 100 Gg Cl/yr for CH3Cl and 200 Gg Cl/yr for CHCl3. These results suggest that the oceans account for about 12% of the global annual emissions of methyl chloride, although until now oceans were thought to be the major source. For chloroform, natural emissions from the oceans and lands appear to be the major sources. For further research, the complete database compiled for this work is available from the archive, which includes a monthly emissions inventory on a 1° × 1° latitude‐longitude grid for oceanic emissions of methyl chloride.

Field study of the emissions of methyl chloride and other halocarbons from biomass burning in Western Africa

A field study of trace gas emissions from biomass burning in Equatorial Africa gave methyl chloride emission ratios of 4.3×10−5±0.8×10−5 mol CH3Cl/mol CO2. Based on the global emission rates for CO2 from biomass burning we estimate a range of 226−904×109 g/y as global emission rate with a best estimate of 515×109 g/y. This is somewhat lower than a previous estimate which has been based on laboratory studies. Nevertheless, our emission rate estimates correspond to 10–40% of the global turnover of methyl chloride and thus support the importance of biomass burning as methyl chloride source. The emission ratios for other halocarbons (CH2Cl2, CHCl3, CCl4, CH3CCl3, C2HCl3, C2Cl4, F-113) are lower. In general there seems to be a substantial decrease with increasing complexity of the compounds and number of halogen atoms. For dichloromethane biomass burning still contributes significantly to the total global budget and in the Southern Hemisphere biomass burning is probably the most important source for atmospheric dichloromethane. For the global budgets of other halocarbons biomass burning is of very limited relevance.

Factors Affecting Methyl Chloride Emissions from Forest Biomass Combustion

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFactors Affecting Methyl Chloride Emissions from Forest Biomass CombustionTimothy E. Reinhardt and Darold E. WardCite this: Environ. Sci. Technol. 1995, 29, 3, 825–832Publication Date (Print):March 1, 1995Publication History Published online1 May 2002Published inissue 1 March 1995https://doi.org/10.1021/es00003a034RIGHTS & PERMISSIONSArticle Views241Altmetric-Citations27LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts