scholarly journals δ 13 C methane source signatures from tropical wetland and rice field emissions

2021 ◽  
Vol 380 (2215) ◽  
Author(s):  
James L. France ◽  
Rebecca E. Fisher ◽  
David Lowry ◽  
Grant Allen ◽  
Marcos F. Andrade ◽  
...  
Keyword(s):  
Rice Field ◽  
Ambient Air ◽  
Atmospheric Methane ◽  
Isotopic Signatures ◽  
Methane Budget ◽  
Significant Seasonal Variation ◽  
Methane Source ◽  
Wetland Extent ◽  
Term Monitoring

The atmospheric methane (CH 4 ) burden is rising sharply, but the causes are still not well understood. One factor of uncertainty is the importance of tropical CH 4 emissions into the global mix. Isotopic signatures of major sources remain poorly constrained, despite their usefulness in constraining the global methane budget. Here, a collection of new δ 13 C CH 4 signatures is presented for a range of tropical wetlands and rice fields determined from air samples collected during campaigns from 2016 to 2020. Long-term monitoring of δ 13 C CH 4 in ambient air has been conducted at the Chacaltaya observatory, Bolivia and Southern Botswana. Both long-term records are dominated by biogenic CH 4 sources, with isotopic signatures expected from wetland sources. From the longer-term Bolivian record, a seasonal isotopic shift is observed corresponding to wetland extent suggesting that there is input of relatively isotopically light CH 4 to the atmosphere during periods of reduced wetland extent. This new data expands the geographical extent and range of measurements of tropical wetland and rice δ 13 C CH 4 sources and hints at significant seasonal variation in tropical wetland δ 13 C CH 4 signatures which may be important to capture in future global and regional models. This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.

scholarly journals Assessment of the theoretical limit in instrumental detectability of Arctic methane sources using <sup>13</sup>C atmospheric signal

2018 ◽  
Author(s):  
Thibaud Thonat ◽  
Marielle Saunois ◽  
Isabelle Pison ◽  
Antoine Berchet ◽  
Thomas Hocking ◽  
...  
Keyword(s):  
Transport Model ◽  
The Arctic ◽  
Atmospheric Methane ◽  
Chemistry Transport Model ◽  
Isotopic Signatures ◽  
Arctic Regions ◽  
Methane Budget ◽  
Source Signal ◽  
Methane Source ◽  
Global Emissions

Abstract. Despite their modest 4 % magnitude compared to global emissions, Arctic methane sources are key elements in closing the global atmospheric methane budget, due to high uncertainties in their quantification and to their strong climate sensitivity. Recent efforts brought together bottom-up quantification approaches (inventories, process-based models) and regional observations of methane concentrations through inverse modelling to better estimate the Arctic methane sources, but the relatively small number of available observations in Arctic regions leaves gaps in fully understanding the drivers and distributions of the different types of methane sources present in the Arctic. Observations of methane isotope ratios could bring new insights on methane processes with increasingly affordable and accurate instruments. Here, we present the source signal that could be observed from methane isotopic measurements if high-resolution observations were available, and thus what requirements should be fulfilled in future instrument deployments in terms of accuracy in order to constrain different emission categories. This theoretical study uses the regional chemistry-transport model CHIMERE driven by different scenarios of isotopic signatures for each regional methane source mix. It is found that if the current network of methane monitoring sites is equipped with instruments measuring the isotopic signal continuously, only sites that are significantly influenced by emission sources could differentiate regional emissions from the background with a reasonable level of confidence. Nevertheless, we show that the detection of individual Arctic sources requires daily accuracies of

scholarly journals Kinetic isotope effects of <sup>12</sup>CH<sub>3</sub>D  + OH and <sup>13</sup>CH<sub>3</sub>D  + OH from 278 to 313 K

2016 ◽  
Vol 16 (7) ◽  
pp. 4439-4449 ◽  
Author(s):  
L. M. T. Joelsson ◽  
J. A. Schmidt ◽  
E. J. K. Nilsson ◽  
T. Blunier ◽  
D. W. T. Griffith ◽  
...  
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
State Theory ◽  
Atmospheric Methane ◽  
Isotopic Signatures ◽  
Budget Analysis ◽  
Kinetic Isotope ◽  
Methane Budget ◽  
Source Signal ◽  
Clumped Isotope

Abstract. Methane is the second most important long-lived greenhouse gas and plays a central role in the chemistry of the Earth's atmosphere. Nonetheless there are significant uncertainties in its source budget. Analysis of the isotopic composition of atmospheric methane, including the doubly substituted species 13CH3D, offers new insight into the methane budget as the sources and sinks have distinct isotopic signatures. The most important sink of atmospheric methane is oxidation by OH in the troposphere, which accounts for around 84 % of all methane removal. Here we present experimentally derived methane + OH kinetic isotope effects and their temperature dependence over the range of 278 to 313 K for CH3D and 13CH3D; the latter is reported here for the first time. We find kCH4/kCH3D = 1.31 ± 0.01 and kCH4/k13CH3D = 1.34 ± 0.03 at room temperature, implying that the methane + OH kinetic isotope effect is multiplicative such that (kCH4/k13CH4)(kCH4/kCH3D) = kCH4/k13CH3D, within the experimental uncertainty, given the literature value of kCH4/k13CH4 = 1.0039 ± 0.0002. In addition, the kinetic isotope effects were characterized using transition state theory with tunneling corrections. Good agreement between the experimental, quantum chemical, and available literature values was obtained. Based on the results we conclude that the OH reaction (the main sink of methane) at steady state can produce an atmospheric clumped isotope signal (Δ(13CH3D) = ln([CH4][13CH3D]/[13CH4][CH3D])) of 0.02 ± 0.02. This implies that the bulk tropospheric Δ(13CH3D) reflects the source signal with relatively small adjustment due to the sink signal (i.e., mainly OH oxidation).

scholarly journals Quantification Method for Electrolytic Sensors in Long-Term Monitoring of Ambient Air Quality

Sensors ◽  
2015 ◽  
Vol 15 (10) ◽  
pp. 27283-27302 ◽  
Author(s):  
Nicholas Masson ◽  
Ricardo Piedrahita ◽  
Michael Hannigan
Keyword(s):  
Air Quality ◽  
Ambient Air ◽  
Ambient Air Quality ◽  
Quantification Method ◽  
Long Term Monitoring ◽  
Term Monitoring

Long-term monitoring of benthic foraminiferal assemblages from Asia's largest tropical coastal lagoon, Chilika, India

2018 ◽  
Vol 99 (2) ◽  
pp. 311-330
Author(s):  
Vandana Kumari Gupta ◽  
Areen Sen ◽  
Ajit K. Pattnaik ◽  
Gurdeep Rastogi ◽  
Punyasloke Bhadury
Keyword(s):  
Coastal Lagoon ◽  
Benthic Foraminifera ◽  
Taxonomic Composition ◽  
Spatial Patterning ◽  
Pattern Diversity ◽  
Significant Seasonal Variation ◽  
Lagoon Environment ◽  
Term Monitoring ◽  
High Diversity

The present study undertaken in the largest coastal lagoon of Asia, Chilika, deals with monthly monitoring of benthic foraminifera assemblages in terms of distribution pattern, diversity and variations in taxonomic composition spanning over a period of 20 months. In total, 13 species of benthic foraminifera represented by eight families were identified in the lagoon. The stations in the Southern sector of the lagoon showed relatively low foraminifera abundance yet high diversity whereas higher abundance and lower diversity were observed in stations located in the Central sector which indicates the spatial patterning of the assemblage. Live foraminifera abundance was sparse in the study area indicating the stressed nature of the lagoon environment. The dissolved nutrient concentration of bottom water reflected significant seasonal variation. The stressed nature of the lagoon is further indicated by the dominance of the genus Ammonia across the inner sectors of the lagoon, a genus known to inhabit impacted habitats. Overall these data can serve as a baseline proxy for understanding palaeontological assemblages of foraminifera in similar shallow-water settings globally.

scholarly journals Centennial evolution of the atmospheric methane budget: what do the carbon isotopes tell us?

2007 ◽  
Vol 7 (8) ◽  
pp. 2119-2139 ◽  
Author(s):  
K. R. Lassey ◽  
D. M. Etheridge ◽  
D. C. Lowe ◽  
A. M. Smith ◽  
D. F. Ferretti
Keyword(s):  
Nuclear Power ◽  
Isotope Composition ◽  
Mixing Ratio ◽  
Atmospheric Methane ◽  
Global Budget ◽  
Polar Ice ◽  
Direct Production ◽  
Methane Budget ◽  
Atmospheric Data ◽  
Methane Source

Abstract. Little is known about how the methane source inventory and sinks have evolved over recent centuries. New and detailed records of methane mixing ratio and isotopic composition (12CH4, 13CH4 and 14CH4) from analyses of air trapped in polar ice and firn can enhance this knowledge. We use existing bottom-up constructions of the source history, including "EDGAR"-based constructions, as inputs to a model of the evolving global budget for methane and for its carbon isotope composition through the 20th century. By matching such budgets to atmospheric data, we examine the constraints imposed by isotope information on those budget evolutions. Reconciling both 12CH4 and 13CH4 budgets with EDGAR-based source histories requires a combination of: a greater proportion of emissions from biomass burning and/or of fossil methane than EDGAR constructions suggest; a greater contribution from natural such emissions than is commonly supposed; and/or a significant role for active chlorine or other highly-fractionating tropospheric sink as has been independently proposed. Examining a companion budget evolution for 14CH4 exposes uncertainties in inferring the fossil-methane source from atmospheric 14CH4 data. Specifically, methane evolution during the nuclear era is sensitive to the cycling dynamics of "bomb 14C" (originating from atmospheric weapons tests) through the biosphere. In addition, since ca. 1970, direct production and release of 14CH4 from nuclear-power facilities is influential but poorly quantified. Atmospheric 14CH4 determinations in the nuclear era have the potential to better characterize both biospheric carbon cycling, from photosynthesis to methane synthesis, and the nuclear-power source.

Interpreting changes in atmospheric methane using satellite and isotopic ratio measurements

2021 ◽  
Author(s):  
Anita Ganesan
Keyword(s):  
Satellite Data ◽  
Field Experiments ◽  
Isotopic Ratio ◽  
Atmospheric Methane ◽  
Isotopic Signatures ◽  
Radiative Efficiency ◽  
Additional Information ◽  
The Past ◽  
Climate Targets

&lt;p&gt;Methane is a potent greenhouse gas with concentrations that are rising in the atmosphere in unexpected ways. Because of its radiative efficiency and because its lifetime in the atmosphere is only around a decade, reducing atmospheric methane concentration is a major component of most pathways designed to meet climate targets. Over the past two decades, observations indicate that there have been substantial changes in the emissions and removal of methane. Yet, years later, we still do not definitively know why methane concentrations plateaued in the 2000s, increased globally after 2007 and then continued to increase at an even faster rate after 2014. This limited understanding impacts our ability to carry out targeted emissions reductions. Here, I discuss two areas of my work in addressing gaps in our knowledge. First, I discuss how high-resolution modeling can extract information from satellite data to quantify long-term changes in emissions and the underlying drivers of these changes. I show that Brazil is a unique example where major sources such as wetlands and cattle are geographically distinct and thus satellite data can be used to examine changes from particular processes. I show how in the absence of this separation, which is the case for many other parts of world, additional information such as isotopic ratios can be used to contribute to the partitioning of methane emissions into underlying sources. I also discuss the limitations in current capability to effectively use isotopic ratio measurements. I show how field experiments and simple models can be used to derive global distributions in the isotopic signatures of major sources such as wetlands, providing more consistency against observations. I discuss how incorrect assumptions about source signature distributions have a major impact on our ability to interpret atmospheric isotopic ratio measurements and that this may be one reason why we have not been able to conclusively interpret the recent atmospheric methane record.&lt;/p&gt;

Long-term monitoring programme of polychlorinated dioxins and polychlorinated furans in ambient air of Catalonia, Spain (1994–2015)

2018 ◽  
Vol 633 ◽  
pp. 738-744 ◽  
Author(s):  
J. Parera ◽  
B.H. Aristizabal ◽  
M.G. Martrat ◽  
M.A. Adrados ◽  
J. Sauló ◽  
...  
Keyword(s):  
Ambient Air ◽  
Monitoring Programme ◽  
Long Term Monitoring ◽  
Term Monitoring

scholarly journals Amazon methane budget derived from multi-year airborne observations highlights regional variations in emissions

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Luana S. Basso ◽  
Luciano Marani ◽  
Luciana V. Gatti ◽  
John B. Miller ◽  
Manuel Gloor ◽  
...  
Keyword(s):  
Temporal Trend ◽  
Lower Troposphere ◽  
Atmospheric Methane ◽  
Tropical Regions ◽  
Methane Budget ◽  
Precipitation Seasonality ◽  
Methane Source ◽  
Global Emissions ◽  
East West

AbstractAtmospheric methane concentrations were nearly constant between 1999 and 2006, but have been rising since by an average of ~8 ppb per year. Increases in wetland emissions, the largest natural global methane source, may be partly responsible for this rise. The scarcity of in situ atmospheric methane observations in tropical regions may be one source of large disparities between top-down and bottom-up estimates. Here we present 590 lower-troposphere vertical profiles of methane concentration from four sites across Amazonia between 2010 and 2018. We find that Amazonia emits 46.2 ± 10.3 Tg of methane per year (~8% of global emissions) with no temporal trend. Based on carbon monoxide, 17% of the sources are from biomass burning with the remainder (83%) attributable mainly to wetlands. Northwest-central Amazon emissions are nearly aseasonal, consistent with weak precipitation seasonality, while southern emissions are strongly seasonal linked to soil water seasonality. We also find a distinct east-west contrast with large fluxes in the northeast, the cause of which is currently unclear.

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