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Abstract We developed a near-real-time estimation method for temporal changes in fossil fuel CO2 (FFCO2) emissions from China for 3 months [January, February, March (JFM)] based on atmospheric CO2 and CH4 observations on Hateruma Island (HAT, 24.06° N, 123.81° E) and Yonaguni Island (YON, 24.47° N, 123.01° E), Japan. These two remote islands are in the downwind region of continental East Asia during winter because of the East Asian monsoon. Previous studies have revealed that monthly averages of synoptic-scale variability ratios of atmospheric CO2 and CH4 (ΔCO2/ΔCH4) observed at HAT and YON in JFM are sensitive to changes in continental emissions. From the analysis based on an atmospheric transport model with all components of CO2 and CH4 fluxes, we found that the ΔCO2/ΔCH4 ratio was linearly related to the FFCO2/CH4 emission ratio in China because calculating the variability ratio canceled out the transport influences. Using the simulated linear relationship, we converted the observed ΔCO2/ΔCH4 ratios into FFCO2/CH4 emission ratios in China. The change rates of the emission ratios for 2020–2022 were calculated relative to those for the preceding 9-year period (2011–2019), during which relatively stable ΔCO2/ΔCH4 ratios were observed. These changes in the emission ratios can be read as FFCO2 emission changes under the assumption of no interannual variations in CH4 emissions and biospheric CO2 fluxes for JFM. The resulting average changes in the FFCO2 emissions in January, February, and March 2020 were 17 ± 8%, − 36 ± 7%, and − 12 ± 8%, respectively, (− 10 ± 9% for JFM overall) relative to 2011–2019. These results were generally consistent with previous estimates. The emission changes for January, February, and March were 18 ± 8%, − 2 ± 10%, and 29 ± 12%, respectively, in 2021 (15 ± 10% for JFM overall) and 20 ± 9%, − 3 ± 10%, and − 10 ± 9%, respectively, in 2022 (2 ± 9% for JFM overall). These results suggest that the FFCO2 emissions from China rebounded to the normal level or set a new high record in early 2021 after a reduction during the COVID-19 lockdown. In addition, the estimated reduction in March 2022 might be attributed to the influence of a new wave of COVID-19 infections in Shanghai.

We developed a near-real-time estimation method for temporal changes in fossil fuel CO2 (FFCO2) emissions from China for 3 months [January, February, March (JFM)] based on atmospheric CO2 and CH4 observations on Hateruma Island (HAT, 24.06° N, 123.81° E) and Yonaguni Island (YON, 24.47° N, 123.01° E), Japan. These two remote islands are in the downwind region of continental East Asia during winter because of the East Asian monsoon. Previous studies have revealed that monthly averages of synoptic-scale variability ratios of atmospheric CO2 and CH4 (ΔCO2/ΔCH4) observed at HAT and YON in JFM are sensitive to changes in continental emissions. From the analysis based on an atmospheric transport model with all components of CO2 and CH4 fluxes, we found that the ΔCO2/ΔCH4 ratio was linearly related to the FFCO2/CH4 emission ratio in China because calculating the variability ratio canceled out the transport influences. Using the simulated linear relationship, we converted the observed ΔCO2/ΔCH4 ratios into FFCO2/CH4 emission ratios in China. The change rates of the emission ratios for 2020–2022 were calculated relative to those for the preceding 9-year period (2011–2019), during which relatively stable ΔCO2/ΔCH4 ratios were observed. These changes in the emission ratios can be read as FFCO2 emission changes under the assumption of no interannual variations in CH4 emissions and biospheric CO2 fluxes for JFM. The resulting average changes in the FFCO2 emissions in January, February, and March 2020 were 17 ± 8%, − 36 ± 7%, and − 12 ± 8%, respectively, (− 10 ± 9% for JFM overall) relative to 2011–2019. These results were generally consistent with previous estimates. The emission changes for January, February, and March were 18 ± 8%, − 2 ± 10%, and 29 ± 12%, respectively, in 2021 (15 ± 10% for JFM overall) and 20 ± 9%, − 3 ± 10%, and − 10 ± 9%, respectively, in 2022 (2 ± 9% for JFM overall). These results suggest that the FFCO2 emissions from China rebounded to the normal level or set a new high record in early 2021 after a reduction during the COVID-19 lockdown. In addition, the estimated reduction in March 2022 might be attributed to the influence of a new wave of COVID-19 infections in Shanghai. [ABSTRACT FROM AUTHOR]

The temporal variation of greenhouse gas concentrations in China during the COVID-19 lockdown in China is analyzed in this work using high resolution measurements of near surface △CO 2 , △CH 4 and △CO concentrations above the background conditions at Lin'an station (LAN), a regional background station in the Yangtze River Delta region. During the pre-lockdown observational period (IOP-1), both △CO 2 and △CH 4 exhibited a significant increasing trend relative to the 2011-2019 climatological mean. The reduction of △CO 2 , △CH 4 and △CO during the lockdown observational period (IOP-2) (which also coincided with the Chinese New Year Holiday) reached up to 15.0 ppm, 14.2 ppb and 146.8 ppb, respectively, and a reduction of △CO 2 /△CO probably due to a dramatic reduction from industrial emissions. △CO 2 , △CH 4 and △CO were observed to keep declining during the post-lockdown easing phase (IOP-3), which is the synthetic result of lower than normal CO 2 emissions from rural regions around LAN coupled with strong uptake of the terrestrial ecosystem. Interestingly, the trend reversed to gradual increase for all species during the later easing phase (IOP-4), with △CO 2 /△CO constantly increasing from IOP-2 to IOP-3 and finally IOP-4, consistent with recovery in industrial emissions associated with the staged resumption of economic activity. On average, △CO 2 declined sharply throughout the days during IOP-2 but increased gradually throughout the days during IOP-4. The findings showcase the significant role of emission reduction in accounting for the dramatic changes in measured atmospheric △CO 2 and △CH 4 associated with the COVID-19 lockdown and recovery. [Display omitted] [ABSTRACT FROM AUTHOR]

Synoptic-scale variabilities of atmospheric CO2 and CH4 observed at Yonagunijima (Yonaguni Island, YON, 24.47°N, 123.01°E) during winter (from January to March) in 1998 - 2020 were examined. The monthly mean variability ratios (ΔCO2/ΔCH4) based on correlation slopes within 24 h time windows showed a clear increasing trend, which is mainly attributed to the unprecedented increase in the fossil fuel-derived CO2 (FFCO2) emissions from China. A similar increasing trend of the ΔCO2/ΔCH4 ratio had been reported for the observation at Hateruma Island (HAT, 24.06°N, 123.81°E), located at approximately 100 km east of YON. Nevertheless, the absolute values for YON were 34 % larger than those for HAT. Additionally, the monthly average in February 2020 for YON showed no marked change, whereas that for HAT showed an abrupt considerable decrease associated with the FFCO2 emission decrease in China presumably caused by the COVID-19 lockdown. Investigating the diurnal variations, we found that the local influences were larger at YON, especially during daytime, than at HAT. Using nighttime data (20-6 LST) and a longer time window (84 h), we succeeded in reducing the local influences and the resulting monthly mean ΔCO2/ΔCH4 ratio showed considerable similarity to that observed at HAT including the abrupt decrease in February 2020. These results convinced us that the ΔCO2/ΔCH4 ratio could be successfully used to investigate the relative emission strength in the upwind region. [ABSTRACT FROM AUTHOR]

Abstract The ACT‐America project is a NASA Earth Venture Suborbital‐2 mission designed to study the transport and fluxes of greenhouse gases. The open and freely available ACT‐America data sets provide airborne in situ measurements of atmospheric carbon dioxide, methane, trace gases, aerosols, clouds, and meteorological properties, airborne remote sensing measurements of aerosol backscatter, atmospheric boundary layer height and columnar content of atmospheric carbon dioxide, tower‐based measurements, and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over the Central and Eastern United States. We conducted 121 research flights during five campaigns in four seasons during 2016–2019 over three regions of the US (Mid‐Atlantic, Midwest and South) using two NASA research aircraft (B‐200 and C‐130). We performed three flight patterns (fair weather, frontal crossings, and OCO‐2 underflights) and collected more than 1,140 h of airborne measurements via level‐leg flights in the atmospheric boundary layer, lower, and upper free troposphere and vertical profiles spanning these altitudes. We also merged various airborne in situ measurements onto a common standard sampling interval, which brings coherence to the data, creates geolocated data products, and makes it much easier for the users to perform holistic analysis of the ACT‐America data products. Here, we report on detailed information of data sets collected, the workflow for data sets including storage and processing of the quality controlled and quality assured harmonized observations, and their archival and formatting for users. Finally, we provide some important information on the dissemination of data products including metadata and highlights of applications of ACT‐America data sets.

The ACT‐America project is a NASA Earth Venture Suborbital‐2 mission designed to study the transport and fluxes of greenhouse gases. The open and freely available ACT‐America data sets provide airborne in situ measurements of atmospheric carbon dioxide, methane, trace gases, aerosols, clouds, and meteorological properties, airborne remote sensing measurements of aerosol backscatter, atmospheric boundary layer height and columnar content of atmospheric carbon dioxide, tower‐based measurements, and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over the Central and Eastern United States. We conducted 121 research flights during five campaigns in four seasons during 2016–2019 over three regions of the US (Mid‐Atlantic, Midwest and South) using two NASA research aircraft (B‐200 and C‐130). We performed three flight patterns (fair weather, frontal crossings, and OCO‐2 underflights) and collected more than 1,140 h of airborne measurements via level‐leg flights in the atmospheric boundary layer, lower, and upper free troposphere and vertical profiles spanning these altitudes. We also merged various airborne in situ measurements onto a common standard sampling interval, which brings coherence to the data, creates geolocated data products, and makes it much easier for the users to perform holistic analysis of the ACT‐America data products. Here, we report on detailed information of data sets collected, the workflow for data sets including storage and processing of the quality controlled and quality assured harmonized observations, and their archival and formatting for users. Finally, we provide some important information on the dissemination of data products including metadata and highlights of applications of ACT‐America data sets. Plain Language Summary: We describe the data collected and produced by the Atmospheric Carbon and Transport – America mission, including airborne and tower‐based measurements of greenhouse gases (e.g., carbon dioxide and methane) and modeled atmospheric mole fractions and regional carbon fluxes of greenhouse gases over North America. In this paper, we briefly describe the data collections and archival including the instruments and methodology used to generate, manage, and distribute the data, and the significance of these new measurements for the study of the North American carbon cycle. Key Points: Atmospheric Carbon and Transport – America (ACT‐America) provides a unique, weather‐oriented collection of atmospheric CO2, CH4, trace gases, and meteorological properties measurementsACT‐America data are free and open to the public from the Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC)ACT‐America data are uniquely suited to improve the accuracy and precision of regional inverse greenhouse gas (GHG) flux estimates [ABSTRACT FROM AUTHOR]

High-affinity methanotrophs in upland soils are responsible for the well-known biological sink of atmospheric methane. However, the vertical distribution pattern of their abundance and activity remains largely unknown. Here, we collected soil samples in 2 cm intervals from the surface to a depth of 40 cm in a typical semiarid steppe in the Loess Plateau of China. We found a bell-shaped distribution of the atmospheric methane-oxidizing potential (atmMOP) along the soil depth, and its peak appeared in the 10–20 cm soil layers. The abundance of methanotrophs (dominated by the upland soil cluster gamma, USCγ) showed a similar vertical distribution pattern and was well correlated with the atmMOP (P < 0.01). Pearson correlation analysis and the structural equation model showed that pH and inorganic nitrogen concentration were the main environmental factors that affecting atmMOP and USCγ abundance. • All the soil layers from the surface to 40 cm deep have atmMOP. • The atmMOP showed a peak between 10-20 cm soil layers. • USCγ dominated the in-situ methanotroph community. • pH and inorganic nitrogen were the main environmental factors affecting atmMOP. [ABSTRACT FROM AUTHOR]

We estimated the CH4 budget in Finland for 2004–2014 using the CTE-CH4 data assimilation system with an extended atmospheric CH4 observation network of seven sites from Finland to surrounding regions (Hyytiälä, Kjølnes, Kumpula, Pallas, Puijo, Sodankylä, and Utö). The estimated average annual total emission for Finland is 0.6 ± 0.5 Tg CH4 yr−1. Sensitivity experiments show that the posterior biospheric emission estimates for Finland are between 0.3 and 0.9 Tg CH4 yr−1, which lies between the LPX-Bern-DYPTOP (0.2 Tg CH4 yr−1) and LPJG-WHyMe (2.2 Tg CH4 yr−1) process-based model estimates. For anthropogenic emissions, we found that the EDGAR v4.2 FT2010 inventory (0.4 Tg CH4 yr−1) is likely to overestimate emissions in southernmost Finland, but the extent of overestimation and possible relocation of emissions are difficult to derive from the current observation network. The posterior emission estimates were especially reliant on prior information in central Finland. However, based on analysis of posterior atmospheric CH4, we found that the anthropogenic emission distribution based on a national inventory is more reliable than the one based on EDGAR v4.2 FT2010. The contribution of total emissions in Finland to global total emissions is only about 0.13%, and the derived total emissions in Finland showed no trend during 2004–2014. The model using optimized emissions was able to reproduce observed atmospheric CH4 at the sites in Finland and surrounding regions fairly well (correlation , bias ppb), supporting adequacy of the observations to be used in atmospheric inversion studies. In addition to global budget estimates, we found that CTE-CH4 is also applicable for regional budget estimates, where small scale (11 in this case) optimization is possible with a dense observation network.

We estimated the CH4 budget in Finland for 2004-2014 using the CTE-CH4 data assimilation system with an extended atmospheric CH4 observation network of seven sites from Finland to surrounding regions (Hyytiälä, Kjølnes, Kumpula, Pallas, Puijo, Sodankylä, and Utö). The estimated average annual total emission for Finland is 0.6±0.5 Tg CH4 yr-1. Sensitivity experiments show that the posterior biospheric emission estimates for Finland are between 0.3 and 0.9 Tg CH4 yr-1, which lies between the LPX-Bern-DYPTOP (0.2 Tg CH4 yr-1) and LPJG-WHyMe (2.2 Tg CH4 yr-1) process-based model estimates. For anthropogenic emissions, we found that the EDGAR v4.2 FT2010 inventory (0.4 Tg CH4 yr-1) is likely to overestimate emissions in southernmost Finland, but the extent of overestimation and possible relocation of emissions are difficult to derive from the current observation network. The posterior emission estimates were especially reliant on prior information in central Finland. However, based on analysis of posterior atmospheric CH4, we found that the anthropogenic emission distribution based on a national inventory is more reliable than the one based on EDGAR v4.2 FT2010. The contribution of total emissions in Finland to global total emissions is only about 0.13%, and the derived total emissions in Finland showed no trend during 2004-2014. The model using optimized emissions was able to reproduce observed atmospheric CH4 at the sites in Finland and surrounding regions fairly well (correlation > 0:75, bias < 67 ppb), supporting adequacy of the observations to be used in atmospheric inversion studies. In addition to global budget estimates, we found that CTE-CH4 is also applicable for regional budget estimates, where small scale (1°x1° in this case) optimization is possible with a dense observation network. [ABSTRACT FROM AUTHOR]

To understand the changes in CH 4 emissions in East Asia, mainly in China, we analyzed the synoptic scale variability (SSV) of CO 2 and CH 4 mole fractions at Anmyeondo (AMY; 36.53°N, 126.32°E, 46 m above sea level) in South Korea using near-surface in-situ observations and an atmospheric chemical transport model (ACTM) to investigate the role of prescribed surface fluxes on SSV. The SSV of the tracers at AMY was mainly caused by emission variations from eastern and northeastern China during the winters in 2010–2020, as indicated by the simulated concentration footprints at AMY observed using the WRF-STILT model. The estimated SSV of ΔCH 4 /ΔCO 2 mole fraction ratios from the observations was 4.2–6.2 ppb ppm−1, with a mean of 5.7 ± 0.93 ppb ppm−1 during the winters in 2010–2020. We also calculated the CH 4 /CO 2 emission ratio from China's total annual fossil-fuel emissions, excluding seasonal sources estimated from the Emission Database for Global Atmospheric Research. We found that the ratio was overestimated by ∼98.1% compared to observations, which was likely driven either due to the overestimation of CH 4 or underestimation of CO 2. We discerned that the model-simulated SSV of the ΔCH 4 /ΔCO 2 ratios generally reproduced the observations when the CH 4 FixCoal simulation case was used. This implies that CH 4 from coal was a major contributor to the observed variations in the winter period ΔCH 4 /ΔCO 2 ratios. However, the model did not reproduce the observed ratio in 2012—this discrepancy requires further study. The trend of ΔCH 4 /ΔCO 2 was a slight decrease over time, which was attributed to the earlier onset of CH 4 emissions relative to fossil-fuel CO 2 , predominantly due to the reduction of CH 4 emissions from coal. In 2013, a relatively low tracer ratio was noted, which was caused by the large contribution of CO 2 from biomass burning. Overall, the observed AMY ΔCH 4 /ΔCO 2 ratios provide an efficient approach for validating the existing estimates of East Asian sectoral emissions of CH 4. • Synoptic scale variability (SSV) of CH 4 and CO 2 at Anmyeondo, South Korea was mainly caused by emission variations from eastern and northeastern China. • Simulated wintertime SSV of CH 4 a from coal was well matched with observations at Anmyeondo during 2010–2020. • EDGAR v6 China anthropogenic CH 4 /CO 2 emission ratio was overestimated against observation based SSV ΔCH 4 /ΔCO 2 mole fractions ratios. • Decline trend of wintertime SSV ΔCH 4 /ΔCO 2 mole fractions ratios Anmyeondo was attributed to a slower growth rate of China anthropogenic CH 4 emission compared to CO 2. • Observed low ΔCH 4 /ΔCO 2 ratio in 2013 was most likely caused by large contribution CO 2 from biomass burning. [ABSTRACT FROM AUTHOR]

The restoration of peatlands is an important strategy to counteract subsidence and loss of biodiversity. However, responses of important microbial soil processes are poorly understood. We assessed functioning, diversity and spatial organization of methanotrophic communities in drained and rewetted peat meadows with different water table management and agricultural practice. Results show that the methanotrophic diversity was similar between drained and rewetted sites with a remarkable dominance of the genus Methylocystis. Enzyme kinetics depicted no major differences, indicating flexibility in the methane (CH4) concentrations that can be used by the methanotrophic community. Short-term flooding led to temporary elevated CH4 emission but to neither major changes in abundances of methane-oxidizing bacteria (MOB) nor major changes in CH4 consumption kinetics in drained agriculturally used peat meadows. Radiolabeling and autoradiographic imaging of intact soil cores revealed a markedly different spatial arrangement of the CH4 consuming zone in cores exposed to near-atmospheric and elevated CH4. The observed spatial patterns of CH4 consumption in drained peat meadows with and without short-term flooding highlighted the spatial complexity and responsiveness of the CH4 consuming zone upon environmental change. The methanotrophic microbial community is not generally altered and harbors MOB that can cover a large range of CH4 concentrations offered due to water-table fluctuations, effectively mitigating CH4 emissions. [ABSTRACT FROM AUTHOR]

The Black Sea is connected to a large drainage area including the European Russian Plain, part of the Alps and southeastern Europe. To study the hydrological changes in this basin over the last 40,000years, we measured specific terrigenous biomarkers for wetland vegetation in well-dated sediments from the northwestern Black Sea, spanning the last glacial period (lacustrine phase) and the Holocene (marine phase). Low abundances of these biomarkers are observed during the North Atlantic ice melting and cooling events known as Heinrich Events 4 to 2, the Last Glacial Maximum and the Younger Dryas Event. Increased biomarker inputs characterize the mild climate phases known as Dansgaard–Oeschger Interstadials, the Bølling/Allerød and Preboreal Warmings indicating increased erosion due to permafrost degradation, higher primary productivity and/or wetland extension in the drainage basin. The final retreat of the Fennoscandian Ice Sheet from the Russian Plain occurs during the early part of Heinrich Event 1 and is characterized by increased biomarker concentrations in a typical series of four deglacial clay layers. For the last glacial period, the correspondence in timing between the biomarker records and the atmospheric CH4 record from ice cores, suggests an important CH4 contribution due to boreal permafrost thawing and wetland emission. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the continuous (1994–2001) and discrete air sample (1991–2001) measurements of atmospheric CH4 from the Waliguan Baseline Observatory located in western China (36°17′N, 100°54′E, 3816masl) are presented and characterized. The CH4 time series show large episodic events on the order of 100ppb throughout the year. During spring, a diurnal cycle with average amplitude of 7ppb and a morning maximum and late afternoon minimum is observed. In winter, a diurnal cycle with average amplitude of 14ppb is observed with an afternoon maximum and morning minimum. Unlike most terrestrial observational sites, no obvious diurnal patterns are present during the summer or autumn. A background data selection procedure was developed based on local horizontal and vertical winds. A selected hourly data set representative of “baseline” conditions was derived with approximately 50% of the valid hourly data. The range of CH4 mixing ratios, annual means, annual increases and mean annual cycle at Waliguan during the 1992–2001 were derived from discrete and continuous data representative of “baseline” conditions and compared to air samples collected at other Northern Hemisphere sites. The range of CH4 monthly means of 1746–1822ppb, average annual means of 1786.7±10.8ppb and mean annual increase of 4.5±4.2ppbyr-1 at Waliguan were inline with measurements from sites located between 30° and 60°N. There were variations observed in the CH4 annual increase patterns at Waliguan that were slightly different from the global pattern. The mean CH4 annual cycle at Waliguan shows an unusual pattern of two gentle peaks in summer and February along with two small valleys in early winter and spring and a mean peak-to-peak amplitude of ∼11ppb, much smaller than amplitudes observed at most other mid- and high-northern latitude sites. The Waliguan CH4 data are strongly influenced by continental Asian CH4 emissions and provide key information for global atmospheric CH4 models. [Copyright &y& Elsevier]

Atmospheric CH 4 mole fractions were observed aboard the R/V Mirai sailing in waters off Alaska in the Arctic Ocean in September 2012–2017 to investigate the CH 4 emissions from the surrounding region, especially from the East Siberian Arctic Shelf (ESAS). The synoptic-scale increases of CH 4 were compared with simulated increases based on a Lagrangian Particle Dispersion Model and monthly CH 4 flux maps determined by a global atmospheric inversion system. There were good agreements between the observed and simulated CH 4 increases, suggesting the validity of CH 4 fluxes from the surrounding areas of the cruise experiments. The CH 4 emissions from the ESAS in September were further optimized in order to minimize the root mean square of the differences between the observed and simulated CH 4 increases. The average (±1σ) of the resulting emission rates was 0.58 ± 0.47 TgCH 4 yr−1, which was much smaller than previously reported estimates. The individual optimized CH 4 emissions varied from −0.1 ± 0.3 to 1.3 ± 0.4 TgCH 4 yr−1, showing a positive correlation with the sea surface temperature and a negative correlation with the ice concentration of the ESAS area in September. These results suggest a possible enhancement of the CH 4 emissions from the ESAS in a warmer future. [ABSTRACT FROM AUTHOR]