Atmospheric CH4 Concentrations Research Articles

Ice Core Methane Analytical Techniques, Chronology and Concentration History Changes: A Review

Ice cores are invaluable in paleoclimate research, offering unique insights into the evolution of the natural environment, human activities, and Earth’s climate system. Methane (CH4) is a crucial greenhouse gas, second only to CO2 in its contribution to global warming, and is one of the primary anthropogenic greenhouse gases. Understanding historical CH4 concentration changes is essential for predicting future trends and informing climate change mitigation strategies. By analyzing gas components trapped in ice core bubbles, we can directly examine the composition of ancient atmospheres. However, there are relatively few comprehensive reviews on ice core CH4 testing techniques, chronology, and concentration history records. In response to this gap, our paper systematically reviews ice core CH4 analytical techniques, chronology, and concentration history changes. Our review indicates that current research on CH4 in non-polar ice cores is insufficient compared to polar ice cores, facing challenges such as high data dispersion, outlier frequency, and the presence of non-atmospheric signals. These limitations hinder our in-depth understanding of CH4 signals in non-polar ice cores, and the reliability of atmospheric CH4 concentration changes they reflect. To address these challenges, we propose exploring and applying advanced testing techniques, such as Continuous Flow Analysis technology, in non-polar ice cores. Additionally, we emphasize the research gap in utilizing CH4 records for age determination in ice core chronology. Future research should focus on this area to advance our understanding of ice core chronology and the history of atmospheric CH4 changes in non-polar regions, ultimately contributing to more effective climate change mitigation efforts.

Coupled anaerobic methane oxidation and metal reduction in soil under elevated CO2.

Continued current emissions of carbon dioxide (CO2 ) and methane (CH4 ) by human activities will increase global atmospheric CO2 and CH4 concentrations and surface temperature significantly. Fields of paddy rice, the most important form of anthropogenic wetlands, account for about 9% of anthropogenic sources of CH4 . Elevated atmospheric CO2 may enhance CH4 production in rice paddies, potentially reinforcing the increase in atmospheric CH4 . However, what is not known is whether and how elevated CO2 influences CH4 consumption under anoxic soil conditions in rice paddies, as the net emission of CH4 is a balance of methanogenesis and methanotrophy. In this study, we used a long-term free-air CO2 enrichment experiment to examine the impact of elevated CO2 on the transformation of CH4 in a paddy rice agroecosystem. We demonstrate that elevated CO2 substantially increased anaerobic oxidation of methane (AOM) coupled to manganese and/or iron oxides reduction in the calcareous paddy soil. We further show that elevated CO2 may stimulate the growth and metabolism of Candidatus Methanoperedens nitroreducens, which is actively involved in catalyzing AOM when coupled to metal reduction, mainly through enhancing the availability of soil CH4 . These findings suggest that a thorough evaluation of climate-carbon cycle feedbacks may need to consider the coupling of methane and metal cycles in natural and agricultural wetlands under future climate change scenarios.

Recent intensification of wetland methane feedback

The positive response of wetland methane (CH4) emissions to climate change is an important yet uncertain Earth-system feedback that amplifies atmospheric CH4 concentrations. Here, using a wetland model, we report intensified wetland CH4 emissions during 2000–2021, corresponding with 2020 and 2021 being exceptional years of growth. Our results highlight the need for sustained monitoring and observations of global wetland CH4 fluxes to document emerging trends, variability and underlying drivers.

Large increases in methane emissions expected from North America's largest wetland complex.

Natural methane (CH4) emissions from aquatic ecosystems may rise because of human-induced climate warming, although the magnitude of increase is highly uncertain. Using an exceptionally large CH4 flux dataset (~19,000 chamber measurements) and remotely sensed information, we modeled plot- and landscape-scale wetland CH4 emissions from the Prairie Pothole Region (PPR), North America's largest wetland complex. Plot-scale CH4 emissions were driven by hydrology, temperature, vegetation, and wetland size. Historically, landscape-scale PPR wetland CH4 emissions were largely dependent on total wetland extent. However, regardless of future wetland extent, PPR CH4 emissions are predicted to increase by two- or threefold by 2100 under moderate or severe warming scenarios, respectively. Our findings suggest that international efforts to decrease atmospheric CH4 concentrations should jointly account for anthropogenic and natural emissions to maintain climate mitigation targets to the end of the century.

The role of rice cultivation in changes in atmospheric methane concentration and the Global Methane Pledge.

Resumption of the increase in atmospheric methane (CH4 ) concentrations since 2007 is of global concern and may partly have resulted from emissions from rice cultivation. Estimates of CH4 emissions from rice fields and abatement potential are essential to assess the contribution of improved rice management in achieving the targets of the Global Methane Pledge agreed upon by over 100 countries at COP26. However, the contribution of CH4 emissions from rice fields to the resumed CH4 growth and the global abatement potential remains unclear. In this study, we estimated the global CH4 emissions from rice fields to be 27 ± 6 Tg CH4 year-1 in the recent decade (2008-2017) based on the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. The trend of CH4 emissions from rice cultivation showed an increase followed by no significant change and then, a stabilization over 1990-2020. Consequently, the contribution of CH4 emissions from rice fields to the renewed increase in atmospheric CH4 concentrations since 2007 was minor. We summarized the existing low-cost measures and showed that improved water and straw management could reduce one-third of global CH4 emissions from rice fields. Straw returned as biochar could reduce CH4 emissions by 12 Tg CH4 year-1 , equivalent to 10% of the total reduction of all anthropogenic emissions. We conclude that other sectors than rice cultivation must have contributed to the renewed increase in atmospheric CH4 concentrations, and that optimizing multiple mitigation measures in rice fields could contribute significantly to the abatement goal outlined in the Global Methane Pledge.

Modelling land use/land cover (LULC) change dynamics, future prospects, and its environmental impacts based on geospatial data models and remote sensing data.

The dynamic change in land use/land cover (LULC) caused by rapid urbanizationhas become a major concern in Lahore, causing a variety of socioeconomic and environmental issues relating to air quality. As a result, it is important to monitor existing LULC change detection, future projection, and the increase in atmospheric pollutants in Lahore. This research work makes use of Landsat, GIOVANNI, SRTM DEM, and vector data. The four key steps of the research approach are as follows: (i) LULC classification from 2000 to 2020 using Lansat data and semi-automatic classification plugin (SCP); (ii) simulation of future prediction using Modules of Land Use Change Evaluation (MOLUSCE) prediction model; (iii) assessment of effects of land use change on air quality using GIOVANNI-NASA product; and (iv) monitoring, change detection, and result interpretation. According to the research findings, there was an increase in metropolitan areas and a decrease in vegetation, barren land, and water bodies for both historical and future projections. The findings also indicated that from 2000 to 2020, about 27.41% of the urban area expanded, with a decline of 42.13% in vegetation, 2.3% in the barren land, and 6.51% in water bodies, respectively. Between 2020 and 2040, the urban area is predicted to increase by 23.15%, while vegetation, barren land, and water bodies are expected to decrease by 28.05%, 1.8%, and 12.31%, respectively. Also, the atmospheric pollutants have been increased including NO2 (1.60%), SO2 (1.02%), CO2 (0.71%), CO (1.56%), O3 (0.15%), and CH4 (0.20%), respectively. And it is projected that by 2040, the average annual atmospheric concentration of NO2, SO2, CO2, CO, O3, and CH4 will be increased by 28.80%, 18.36%, 12.78%, 28.08%, 2.70%, and 3.60%, respectively. In addition, it was also observed that the majority of the city's urban area expansion was found in the city's eastern and southern regions. Therefore, government should focus on natural resource conservation especially vegetation cover to reduce air pollutants concentration and the LULC effect.

Spatial pattern of orbital-to millennial-scale East Asian stalagmite δ18O variations during MIS 3

The Asian hydroclimate variability during the early and middle Marine Isotope Stage (MIS) 3 was reconstructed from a high-resolution stalagmite δ18O record from Qixing Cave in southern China, which exhibited an extraordinarily strong precessional cycle. When compared with other cave records (mostly) from East Asia, covering a latitudinal transect from 23° to 38°N, it can be found that the magnitude of precessional-scale stalagmite δ18O variations decreases when the latitude increases, approximately from 3‰ to 1‰. In contrast, the amplitude of Heinrich stadials (HSs) in these stalagmite δ18O records enhances with increasing latitudes, from 1‰ to 2‰, reflecting an alleviated effect of high-latitude climate changes on the low-latitude hydroclimate, or a relative contribution from Westerlies-borne and near-sourced 18O-enriched moisture at northern China. In southern China, orbital-scale changes in stalagmite δ18O closely match variations of the atmospheric CH4 concentration and δ18O of the atmospheric O2, suggesting a coherent response of low-latitude ecological and hydrological processes. In addition, a weaker precessional cycle in northern China is possibly related to the relative supply of near-sourced moisture source, where the Westerly wind can exert a substantial role. Therefore, precessional to millennial-scale changes in East Asian stalagmite δ18O records could be further modulated by local processes, rendering them a spatially contrasting trait. A pervasive imprint of muted precessional rainfall changes in loess records from northern China suggests a regionally distinct rhythm of moisture availability, in agreement with the stalagmite records from higher latitudes.

Plant community mediated methane uptake in response to increasing nitrogen addition level in a saline-alkaline grassland by rhizospheric effects

Methane (CH4) uptake in dryland ecosystems is a pathway in mitigating atmospheric CH4 concentrations. A number of studies have demonstrated that nitrogen availability is a key regulator of the CH4 oxidation process. However, how plants mediate soil CH4 oxidation in response to N addition, particularly in saline-alkaline grasslands in the vast regions of the northern China, has received little attention. We conducted a 3-yr (2017–2019) in-situ experiment with eight N addition levels to examine the effect of N on soil CH4 oxidation, and to explore the linkages between the N-induced changes of plant community and the seasonal dynamics of CH4 in a saline-alkaline grassland.We found that the saline-alkaline grassland was a weak CH4 sink displaying nonlinear CH4 uptake levels in response to N additions, possibly due to the nonlinear changes in the abundance of key functional genes (pmoA) that were responsible for CH4 oxidation. The changes in plant productivity and diversity that were induced by N additions explained 21 % of the variations in CH4 uptake. The N-induced increase in productivity indirectly enhanced CH4 uptake at N addition rates of <10 g m−2 yr−1, while the decrease in biodiversity indirectly inhibited CH4 uptake when N addition exceeded 10 g m−2 yr−1. The N-induced changes in the plant community can affect CH4 uptake, mainly through the rhizospheric effects of plants. In conclusion, our findings underscore the importance of rhizosphere when assessing the CH4 uptake in saline-alkaline grassland ecosystems.

One year of spectroscopic high‐frequency measurements of atmospheric CO2, CH4, H2O and δ13C‐CO2 at an Australian Savanna site

AbstractWe provide a 1‐year dataset of atmospheric surface CO2, CH4 and H2O concentrations and δ13C‐CO2 values from an Australian savanna site. These semi‐arid ecosystems act as carbon sinks in wet years but the persistence of the sink in dry years is uncertain. The dataset can be used to constrain uncertainties in modelling of greenhouse gas budgets, improve algorithms for satellite measurements and characterize the role of vegetation and soil in modulating atmospheric CO2 concentrations. We found pronounced seasonal variations in daily mean CO2 concentrations with an increase (by 5–7 ppmv) after the first rainfall of the wet season in early December with peak concentrations maintained until late January. The CO2 increase reflected the initiation of rapid microbial respiration from soil and vegetation sources upon initial wetting. As the wet season progressed, daily CO2 concentrations were variable, but generally decreased back to dry season levels as CO2 assimilation by photosynthesis increased. Mean daily concentrations of CH4 increased in the wet season by up to 0.2 ppmv relative to dry season levels as the soil profile became waterlogged after heavy rainfall events. During the dry season there was regular cycling between maximum CO2/minimum δ13C‐CO2 at night and minimum CO2/maximum δ13C‐CO2 during the day. In the wet season diel patterns were less regular in response to variable cloud cover and rainfall. CO2 isotope data showed that in the wet season, surface CO2 was predominantly a two‐component mixture influenced by C3 plant assimilation (day) and soil/plant respiration (night), while regional background air from higher altitudes represented an additional CO2 source in the dry season. Higher wind speeds during the dry season increased vertical mixing compared to the wet season. In addition, night‐time advection of high‐altitude air during low temperature conditions also promoted mixing in the dry season.

Spatiotemporal Variations of XCH4 across China during 2003–2021 Based on Observations from Multiple Satellites

Atmospheric methane (CH4) is an important greenhouse gas that can reflect variations of CH4 emissions and sinks. This study aimed to detect spatial and temporal variations of atmospheric CH4 concentrations in China during 2003–2021 based on CH4 column-averaged dry-air mole fraction (XCH4) products from three satellites, namely, Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), Greenhouse Gases Observing Satellite (GOSAT), and Copernicus Sentinel-5 Precursor (S5P). The results revealed that XCH4 observed from three satellites showed high agreement in spatiotemporal variations and demonstrated good consistency with ground station measurements. The correlation coefficients (r) between the three satellites were 0.72 and 0.73, and the correlation coefficients for the ground stations were 0.79, 0.66, 0.03, 0.21, 0.70, and 0.80. The spatial distribution of XCH4 in China was generally high in the east and low in the west and close to that of CH4 emissions, indicating that CH4 emission sources dominated the spatial variations of atmospheric XCH4. From 2003 to 2006, XCH4 remained stable with an annual growth rate of 0.51 ppb·yr−1 and then abruptly increased with an overall growth rate of 6.96 ppb·yr−1. There were obvious seasonal changes in XCH4, with peaks in autumn and summer and nadir in winter and spring. These seasonal variations of XCH4 were related to CH4 emissions from rice planting. Rice cultivation areas generally had high XCH4 concentrations, and the growth cycle of rice plants significantly contributed to seasonal variations of XCH4 in the main rice planting areas. These results provide scientific data that could encourage decision-makers to enact policies and processes to reduce methane emissions.

Recent progress of catalytic methane combustion over transition metal oxide catalysts.

Methane (CH4) is one of the cleanest fossil fuel resources and is playing an increasingly indispensable role in our way to carbon neutrality, by providing less carbon-intensive heat and electricity worldwide. On the other hand, the atmospheric concentration of CH4 has raced past 1,900 ppb in 2021, almost triple its pre-industrial levels. As a greenhouse gas at least 86 times as potent as carbon dioxide (CO2) over 20 years, CH4 is becoming a major threat to the global goal of deviating Earth temperature from the +2°C scenario. Consequently, all CH4-powered facilities must be strictly coupled with remediation plans for unburned CH4 in the exhaust to avoid further exacerbating the environmental stress, among which catalytic CH4 combustion (CMC) is one of the most effective strategies to solve this issue. Most current CMC catalysts are noble-metal-based owing to their outstanding C–H bond activation capability, while their high cost and poor thermal stability have driven the search for alternative options, among which transition metal oxide (TMO) catalysts have attracted extensive attention due to their Earth abundance, high thermal stability, variable oxidation states, rich acidic and basic sites, etc. To date, many TMO catalysts have shown comparable catalytic performance with that of noble metals, while their fundamental reaction mechanisms are explored to a much less extent and remain to be controversial, which hinders the further optimization of the TMO catalytic systems. Therefore, in this review, we provide a systematic compilation of the recent research advances in TMO-based CMC reactions, together with their detailed reaction mechanisms. We start with introducing the scientific fundamentals of the CMC reaction itself as well as the unique and desirable features of TMOs applied in CMC, followed by a detailed introduction of four different kinetic reaction models proposed for the reactions. Next, we categorize the TMOs of interests into single and hybrid systems, summarizing their specific morphology characterization, catalytic performance, kinetic properties, with special emphasis on the reaction mechanisms and interfacial properties. Finally, we conclude the review with a summary and outlook on the TMOs for practical CMC applications. In addition, we also further prospect the enormous potentials of TMOs in producing value-added chemicals beyond combustion, such as direct partial oxidation to methanol.

Large Methane Emission Fluxes Observed From Tropical Wetlands in Zambia

AbstractMethane (CH4) is a potent greenhouse gas with a warming potential 84 times that of carbon dioxide (CO2) over a 20‐year period. Atmospheric CH4 concentrations have been rising since the nineteenth century but the cause of large increases post‐2007 is disputed. Tropical wetlands are thought to account for ∼20% of global CH4 emissions, but African tropical wetlands are understudied and their contribution is uncertain. In this work, we use the first airborne measurements of CH4 sampled over three wetland areas in Zambia to derive emission fluxes. Three independent approaches to flux quantification from airborne measurements were used: Airborne mass balance, airborne eddy‐covariance, and an atmospheric inversion. Measured emissions (ranging from 5 to 28 mg m−2 hr−1) were found to be an order of magnitude greater than those simulated by land surface models (ranging from 0.6 to 3.9 mg m−2 hr−1), suggesting much greater emissions from tropical wetlands than currently accounted for. The prevalence of such underestimated CH4 sources may necessitate additional reductions in anthropogenic greenhouse gas emissions to keep global warming below a threshold of 2°C above preindustrial levels.

The first simultaneous and continuous underway measurements of atmospheric gaseous elemental mercury, carbon dioxide and methane in the marine boundary layer: Results of cruise study in the Sea of Japan in May 2018

This paper presents the results of the first simultaneous measurements of gaseous elemental mercury (GEM) and greenhouse gases (CH4 and CO2) in the marine boundary layer over the Sea of Japan. Continuous underway measurements of atmospheric GEM, CH4 and CO2 concentrations were carried out aboard the R/V Akademik M.A. Lavrentiev from 4 to May 26, 2018. GEM concentrations (range: 0.4–1.6 ng/m3; mean ± standard deviation (SD): 1.0 ± 0.2 ng/m3; N = 938) were lower than both the atmospheric background and previously observed values in this area. Concentrations of CH4 (range: 1922.6–2010.6 ppb; mean ± SD: 1942.2 ± 10.8 ppb) and CO2 (range: 408.9–436.1 ppm; mean ± SD: 412.5 ± 2.5 ppm) were higher than both the average global atmospheric concentrations in May, and the average annual values. Concentration-weighted trajectory (CWT) analysis highlighted the Korean peninsula, northeastern China, southern Primorsky Krai (Russia) and the southwestern coast of Hokkaido (Japan) as potential source areas influencing atmospheric GEM, CH4 and CO2 concentrations during the cruise. Vertical distribution of the CWT values for all the measured gaseous species identified the lower atmosphere up to 1000 m as source layer. The same layer was also characterized by lower CWT values for CH4 and CO2, which were associated with atmospheric transport from the central part of the Sea of Japan. With increasing altitude, the CWT values for GEM and CH4 decreased, while the CO2 values began to rise from 2000 m reflecting the respiration of terrestrial ecosystems and, possibly, atmospheric transport from fires in western Russia.The study shows potential source regions influencing GEM, CH4 and CO2 concentrations in the atmosphere over the Sea of Japan in May 2018.

Comparing national greenhouse gas budgets reported in UNFCCC inventories against atmospheric inversions

Abstract. In support of the global stocktake of the Paris Agreement on climate change, this study presents a comprehensive framework to process the results of an ensemble of atmospheric inversions in order to make their net ecosystem exchange (NEE) carbon dioxide (CO2) flux suitable for evaluating national greenhouse gas inventories (NGHGIs) submitted by countries to the United Nations Framework Convention on Climate Change (UNFCCC). From inversions we also deduced anthropogenic methane (CH4) emissions regrouped into fossil and agriculture and waste emissions, as well as anthropogenic nitrous oxide (N2O) emissions. To compare inversion results with national reports, we compiled a new global harmonized database of emissions and removals from periodical UNFCCC inventories by Annex I countries, and from sporadic and less detailed emissions reports by non-Annex I countries, given by national communications and biennial update reports. No gap filling was applied. The method to reconcile inversions with inventories is applied to selected large countries covering ∼90 % of the global land carbon uptake for CO2 and top emitters of CH4 and N2O. Our method uses results from an ensemble of global inversions produced by the Global Carbon Project for the three greenhouse gases, with ancillary data. We examine the role of CO2 fluxes caused by lateral transfer processes from rivers and from trade in crop and wood products and the role of carbon uptake in unmanaged lands, both not accounted for by NGHGIs. Here we show that, despite a large spread across the inversions, the median of available inversion models points to a larger terrestrial carbon sink than inventories over temperate countries or groups of countries of the Northern Hemisphere like Russia, Canada and the European Union. For CH4, we find good consistency between the inversions assimilating only data from the global in situ network and those using satellite CH4 retrievals and a tendency for inversions to diagnose higher CH4 emission estimates than reported by NGHGIs. In particular, oil- and gas-extracting countries in central Asia and the Persian Gulf region tend to systematically report lower emissions compared to those estimated by inversions. For N2O, inversions tend to produce higher anthropogenic emissions than inventories for tropical countries, even when attempting to consider only managed land emissions. In the inventories of many non-Annex I countries, this can be tentatively attributed to a lack of reporting indirect N2O emissions from atmospheric deposition and from leaching to rivers, to the existence of natural sources intertwined with managed lands, or to an underestimation of N2O emission factors for direct agricultural soil emissions. Inversions provide insights into seasonal and interannual greenhouse gas fluxes anomalies, e.g., during extreme events such as drought or abnormal fire episodes, whereas inventory methods are established to estimate trends and multi-annual changes. As a much denser sampling of atmospheric CO2 and CH4 concentrations by different satellites coordinated into a global constellation is expected in the coming years, the methodology proposed here to compare inversion results with inventory reports (e.g., NGHGIs) could be applied regularly for monitoring the effectiveness of mitigation policy and progress by countries to meet the objective of their pledges. The dataset constructed by this study is publicly available at https://doi.org/10.5281/zenodo.5089799 (Deng et al., 2021).

Spatial Variability and Hotspots of Methane Concentrations in a Large Temperate River

Rivers are significant sources of greenhouse gases (GHGs; e.g., CH4 and CO2); however, our understanding of the large-scale longitudinal patterns of GHG emissions from rivers remains incomplete, representing a major challenge in upscaling. Local hotspots and moderate heterogeneities may be overlooked by conventional sampling schemes. In August 2020 and for the first time, we performed continuous (once per minute) CH4 measurements of surface water during a 584-km-long river cruise along the German Elbe to explore heterogeneities in CH4 concentration at different spatial scales and identify CH4 hotspots along the river. The median concentration of dissolved CH4 in the Elbe was 112 nmol L−1, ranging from 40 to 1,456 nmol L−1 The highest CH4 concentrations were recorded at known potential hotspots, such as weirs and harbors. These hotspots were also notable in terms of atmospheric CH4 concentrations, indicating that measurements in the atmosphere above the water are useful for hotspot detection. The median atmospheric CH4 concentration was 2,033 ppb, ranging from 1,821 to 2,796 ppb. We observed only moderate changes and fluctuations in values along the river. Tributaries did not obviously affect CH4 concentrations in the main river. The median CH4 emission was 251 μmol m−2 d−1, resulting in a total of 28,640 mol d−1 from the entire German Elbe. Similar numbers were obtained using a conventional sampling approach, indicating that continuous measurements are not essential for a large-scale budget. However, we observed considerable lateral heterogeneity, with significantly higher concentrations near the shore only in reaches with groins. Sedimentation and organic matter mineralization in groin fields evidently increase CH4 concentrations in the river, leading to considerable lateral heterogeneity. Thus, river morphology and structures determine the variability of dissolved CH4 in large rivers, resulting in smooth concentrations at the beginning of the Elbe versus a strong variability in its lower parts. In conclusion, groin construction is an additional anthropogenic modification following dam building that can significantly increase GHG emissions from rivers.

Analysis of 5.5 years of atmospheric CO2, CH4, CO continuous observations (2014–2020) and their correlations, at the Observatoire de Haute Provence, a station of the ICOS-France national greenhouse gases observation network

Since 2014, a 100 m tall tower measures continuously greenhouse gases at the Observatoire de haute Provence (OHP) located in the southeast of France (43° 55′ 51″ N, 5° 42′ 48″ E) as a monitoring station of the French National Greenhouse Gases Observation network (ICOS-Fr). This rural station allows to study the short, mid, and long terms variability of atmospheric CO2, CH4 and CO concentrations at the continental, regional and local scales in a region characterized by a Mediterranean climate. Measurements are performed using cavity ring-down spectroscopy at three levels above ground level (AGL); 10 m, 50 m and 100 m. Using the ICOS European Infrastructure procedure to calibrate and ensure the data quality control, the precision of our datasets matches the international WMO/GAW recommendations. Time series from July 2014 to February 2020 were analysed. We inferred a mean annual growth rate at 100 m AGL of 2.7 ppm/year for CO2 (7.8 ppb/year for CH4) over the period of study, whereas no significant annual growth rate was found for CO. These growth rates are comparable to other remote ICOS and WMO/GAW sites. A seasonal amplitude of 13 ppm, 30 ppb, 45 ppb was found for atmospheric CO2, CH4 and CO, respectively. As expected, the amplitude of the diurnal cycle of these three species varies in function of the season, from 2.6 (1.6) ppm in winter and 10.7 (6.6) ppm in summer for CO2, 3.7 (5.1) and 7.7 (7.1) ppb for CH4, and contrary to CO2 and CH4 smaller amplitude in summer with 2.15 (2.5) ppb and 9.3 (8.9) ppb in winter for CO at 10 m (100 m) AGL. Significant correlations (R2 between 0.67 and 0.91) between the three species have been detected, especially in the winter season. Using thresholds on wind speed and on the standard variation of hourly concentrations, more than 16% of the data were identified to be enriched either: 1/by regional anthropogenic plumes; 2/during stable synoptic conditions inducing the accumulation of anthropogenic emissions in the atmospheric boundary layer (13%); and 3/by local's sources inducing short pollution events (3%). On average, ΔCO/Δ CO2 ratios of 3.72 ± 0.06 ppb/ppm and 0.8 ± 0.2 ppb/ppm for Δ CH4/ΔCO were inferred during local pollution events in winter and are typical of traffic and residential heating as given by the local bottom-up emissions inventory delivered by the regional air quality agency ATMOSUD. Adding specific tracers or isotopic measurements would be very interesting to distinguish anthropogenic sources and monitor the evolution of their characteristics as emission ratios at the OHP station. Filtering out these conditions, about 84% of the data are not undergoing the influence of local and regional anthropogenic plumes, and are thus representative of “background” CO2, CO and CH4 concentrations at the local to the regional scales. These background conditions are shown to be dependent on wind speed and direction.

Spatiotemporal Geostatistical Analysis and Global Mapping of CH4 Columns from GOSAT Observations

Methane (CH4) is one of the most important greenhouse gases causing the global warming effect. The mapping data of atmospheric CH4 concentrations in space and time can help us better to understand the characteristics and driving factors of CH4 variation as to support the actions of CH4 emission reduction for preventing the continuous increase of atmospheric CH4 concentrations. In this study, we applied a spatiotemporal geostatistical analysis and prediction to develop an approach to generate the mapping CH4 dataset (Mapping-XCH4) in 1° grid and three days globally using column averaged dry air mole fraction of CH4 (XCH4) data derived from observations of the Greenhouse Gases Observing Satellite (GOSAT) from April 2009 to April 2020. Cross-validation for the spatiotemporal geostatistical predictions showed better correlation coefficient of 0.97 and a mean absolute prediction error of 7.66 ppb. The standard deviation is 11.42 ppb when comparing the Mapping-XCH4 data with the ground measurements from the total carbon column observing network (TCCON). Moreover, we assessed the performance of this Mapping-XCH4 dataset by comparing with the XCH4 simulations from the CarbonTracker model and primarily investigating the variations of XCH4 from April 2009 to April 2020. The results showed that the mean annual increase in XCH4 was 7.5 ppb/yr derived from Mapping-XCH4, which was slightly greater than 7.3 ppb/yr from the ground observational network during the past 10 years from 2010. XCH4 is larger in South Asia and eastern China than in the other regions, which agrees with the XCH4 simulations. The Mapping-XCH4 shows a significant linear relationship and a correlation coefficient of determination (R2) of 0.66, with EDGAR emission inventories over Monsoon Asia. Moreover, we found that Mapping-XCH4 could detect the reduction of XCH4 in the period of lockdown from January to April 2020 in China, likely due to the COVID-19 pandemic. In conclusion, we can apply GOSAT observations over a long period from 2009 to 2020 to generate a spatiotemporally continuous dataset globally using geostatistical analysis. This long-term Mpping-XCH4 dataset has great potential for understanding the spatiotemporal variations of CH4 concentrations induced by natural processes and anthropogenic emissions at a global and regional scale.

The Spatial and Temporal Distribution Patterns of XCH4 in China: New Observations from TROPOMI

Methane is the second most important greenhouse gas after carbon dioxide. The intensity and distribution of methane source/sink in China are unknown. We collected the column-averaged dry air mixing ratio of CH4 (abbreviated as XCH4 hereafter) from TROPOMI for the period from 2018 to 2021, to study spatial distribution and temporal change of atmospheric CH4 concentration, providing clues and foundations for understanding the source/sink in China. It was found that the distribution of XCH4 is roughly high in the East, low in the West, high in the South and low in the North. Additionally, an evidently positive linear relationship between XCH4 and population density was witnessed, suggesting anthropogenic emissions may account for a large portion of total methane emissions. XCH4 exhibits evident seasonal characteristics, with the peak in summer and trough in winter, regardless of the different regions. Moreover, we used XCH4 anomalies to identify the emission sources and found its great potential in the detection of methane emission from mining plants, landfill, rice fields and even geological fracture zones.

Spatiotemporal changes in early human land use during the Holocene throughout the Yangtze River Basin, China

The contribution of early human activity to the increase in atmospheric CH4 content during the middle to late-Holocene is still debated. The quantitative reconstruction of past changes in land use by early rice agriculture is a key to resolving the issue, because large uncertainties still exist in current prehistoric land use estimates, owing to a lack of direct records. In this study, we used the combination of archaeological data (the area and distribution of archaeological sites) and an improved prehistoric land use model (PLUM) to determine the spatiotemporal changes in land use by rice agriculture throughout the Yangtze River Valley, China, which was the origin and centre of the development of rice cultivation. The results indicate that the area devoted to rice agriculture increased during 10–2 ka BP, and that a significant increase occurred at ~5 ka BP accompanied by a spatial expansion from the northern part of the valley to the entire valley. However, the rice land use area decreased slightly during 4–3 ka BP but then increased after 3 ka BP. We estimate that the CH4 emissions from the rice cultivated area in the Yangtze River Valley increased from ~0.001 (±0.001) to ~1.3 (±0.6) Tg/year during 10–2 ka BP, and the resulting atmospheric CH4 concentrations increased from ~0.004 (±0.002) to ~4.1 (±2.0) ppb, which accounted for 3 (±2)–9 (±5) % of the ‘anomalous atmospheric CH4 increase’ during 5–2 ka BP.

Estimation of methane emission from an urban wastewater treatment plant applying inverse Gaussian model.

The methane (CH4) emissions from urban sources are increasing, and they depend on the processes and technologies applied in each one. Thus, studying them individually to quantify their emissions and understand their behavior to design CH4 mitigation strategies is meaningful. Although many studies have been carried out in different cities worldwide, the complex methodologies and technologies applied are not readily available in developing countries. The main objective of this work is to apply a simple and inexpensive methodology to collect air samples in urban areas using syringes with a three-way stopcock. Considering the baseline concentration in different urban zones, the WWTP contribution to atmospheric CH4 concentration was assessed. Moreover, it was possible to estimate the CH4 emission rate from the source by applying the inverse Gaussian model. The atmospheric CH4 concentrations inside and around the WWTP varied from 2.04 to 32.78ppm. Most of the highest concentrations were found inside the WWTP; however, high concentrations were found up to 500m from its center. The values in the urban zones were between 2.06 and 3.52ppm, consistently higher in the area with the highest population density. Finally, considering the WWTP as a single source and according to the operational and atmospheric conditions during the studied period, the mean CH4 emission rate from this source was 2.08E + 04μgs-1. The proposed sampling methodology could be applied to estimate CH4 emission rates from fixed sources in areas with overlapping sources.