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Limiting the rise in global mean temperatures relies on reducing carbon dioxide (CO 2 ) emissions and on the removal of CO 2 by land carbon sinks. China is currently the single largest emitter of CO 2 , responsible for approximately 27 per cent (2.67 petagrams of carbon per year) of global fossil fuel emissions in 2017 1 . Understanding of Chinese land biosphere fluxes has been hampered by sparse data coverage 2 – 4 , which has resulted in a wide range of a posteriori estimates of flux. Here we present recently available data on the atmospheric mole fraction of CO 2 , measured from six sites across China during 2009 to 2016. Using these data, we estimate a mean Chinese land biosphere sink of −1.11 ± 0.38 petagrams of carbon per year during 2010 to 2016, equivalent to about 45 per cent of our estimate of annual Chinese anthropogenic emissions over that period. Our estimate reflects a previously underestimated land carbon sink over southwest China (Yunnan, Guizhou and Guangxi provinces) throughout the year, and over northeast China (especially Heilongjiang and Jilin provinces) during summer months. These provinces have established a pattern of rapid afforestation of progressively larger regions 5 , 6 , with provincial forest areas increasing by between 0.04 million and 0.44 million hectares per year over the past 10 to 15 years. These large-scale changes reflect the expansion of fast-growing plantation forests that contribute to timber exports and the domestic production of paper 7 . Space-borne observations of vegetation greenness show a large increase with time over this study period, supporting the timing and increase in the land carbon sink over these afforestation regions. Newly available atmospheric carbon dioxide measurements from six sites across China during 2009 to 2016 indicate a larger land carbon sink than previously thought, reflecting increased afforestation.

Understanding the dynamics of terrestrial carbon sources and sinks is crucial for addressing climate change, yet significant uncertainties remain at regional scales. We developed the Monitoring and Evaluation of Greenhouse gAs Flux (MEGA) inversion system with satellite data assimilation and applied it to China using OCO-2 V11.1r XCO2 retrievals. Our results show that China’s terrestrial ecosystems acted as a carbon sink of 0.28 ± 0.15 PgC yr−1 during 2018–2023, consistent with other inversion estimates. Validation against surface CO2 flask measurements demonstrated significant improvement, with RMSE and MAE reduced by 30%–46% and 24–44%, respectively. Six sets of prior sensitivity experiments conclusively demonstrated the robustness of MEGA. In addition, this study is the first to systematically compare model-derived and observation-based background fields in satellite data assimilation. Ten sets of background sensitivity experiments revealed that model-based background fields exhibit superior capability in resolving seasonal flux dynamics, though their performance remains contingent on three key factors: (1) initial fields, (2) flux fields, and (3) flux masks (used to control regional flux switches). These findings highlight the potential for further refinement of the atmospheric inversion system.

Triple collocation (TC) shows potential in estimating the errors of various geographical data in the absence of the truth. In this study, the TC techniques are first applied to evaluate the performances of multiple column-averaged dry air CO2 mole fraction (XCO2) estimates derived from the Greenhouse Gases Observing Satellite (GOSAT), the Orbiting Carbon Observatory 2 (OCO-2) and the CarbonTracker model (CT2019B) at a global scale. A direct evaluation with the Total Carbon Column Observing Network (TCCON) measurements is also employed for comparison. Generally, the TC-based evaluation results are consistent with the direct evaluation results on the overall performances of three XCO2 products, in which the CT2019B performs best, followed by OCO-2 and GOSAT. Correlation coefficient estimates of the TC show higher consistency and stronger robustness than root mean square error estimates. TC-based error estimates show that most of the terrestrial areas have larger error than the marine areas overall, especially for the GOSAT and CT2019B datasets. The OCO-2 performs well in areas where CT2019B or GOSAT have large errors, such as most of China except the northwest, and Russia. This study provides a reference for characterizing the performances of multiple CO2 products from another perspective.

Vertical profiles of methane (CH4) are essential for validating satellite observations and quantifying regional sources and sinks. This study presents the first two high‐resolution CH4 profiles (0–25 km) over southeastern China, an economically developed region, using AirCore measurements. The profiles exhibited distinct variations: CH4 increased from 25 to 15 km, remained stable (15–6 km), decreased sharply (6–3 km), then rose toward the surface (∼600 ppb range). While trends align with observations in northwest China, concentrations were higher. Wind patterns and balloon trajectories influenced the profiles, with long‐range air mass transport from coastal megacities elevating upper‐atmosphere CH4. Comparisons with TCCON, TROPOMI, and GOSAT‐2 revealed 26–39 ppb discrepancies in column‐averaged CH4, exposing resolution limitations and retrieval uncertainties. Pronounced day‐to‐day variability highlight influence from meteorological conditions and regional transport. These findings emphasize the need for higher spatiotemporal resolution monitoring to improve CH4 assessments and climate modeling.

The Asian summer monsoon (ASM) region is a key region transporting air to the upper troposphere (UT), significantly influencing the distribution and concentration of trace gases, including methane (CH4), an important greenhouse gas. We investigate the seasonal enhancement of CH4 in the UT over the ASM region, utilizing retrievals from the Atmospheric Infrared Sounder (AIRS), model simulations and in-situ measurements. Both the AIRS data and model simulation reveal a substantial enhancement in CH4 concentrations within the active monsoon region of up to 3%, referring to the zonal means, and of up to 6% relative to the pre-monsoon season. Notably, the spatial distribution of the CH4 plume demonstrates a southwestward shift in the AIRS retrievals, in contrast to the model simulations, which predict a broader enhancement, including a significant increase to the east. A cross-comparison with in-situ measurements, including AirCore measurements over the Tibetan Plateau and airline sampling across the ASM anticyclone (ASMA), favors the enhancement represented by model simulation. Remarkable CH4 enhancement over the west Pacific is also evidenced by in-situ data and simulation as a dynamical extension of the ASMA. Our findings underscore the necessity for cautious interpretation of satellite-derived CH4 distributions, and highlight the critical role of in-situ data in anchoring the assimilation of CH4.

We present data and analysis of a set of balloon‐borne sounding profiles, which includes co‐located O3, CO, CH4, and particles, over the northern Tibetan Plateau during an Asian summer monsoon (ASM) season. These novel measurements shed light on the ASM transport behavior near the northern edge of the anticyclone. Joint analyses of these species with the temperature and wind profiles and supported by back trajectory modeling identify three distinct transport processes that dominate the vertical chemical structure in the middle troposphere, upper troposphere (UT), and the tropopause region. The correlated changes in profile structures in the middle troposphere highlight the influence of the strong westerly jet. Elevated constituent concentrations in the UT identify the main level of convective transport at the upstream source regions. Observed higher altitude maxima for CH4 characterize the airmasses' continued ascent following convection. These data complement constituent observations from other parts of the ASM anticyclone. Plain Language Summary Asian summer monsoon deep convection transports surface pollutants to the stratosphere. Although satellite data have provided clear evidence of this transport, in situ measurements are critical for characterizing how monsoon is vertically re‐distributing the regional emissions. We report new balloon‐borne measurements over the Tibetan Plateau that provide a unique data set on the northern edge of the anticyclone, complementing other observations. Key Points A novel set of in‐situ profile measurements of O3, CO, CH4 and particles from Tibetan Plateau during Asian summer monsoon are presented Joint analyses of the profiles provide insights into transport processes controlling the northern edge of the Asian monsoon anticyclone Observed CO profile maxima at 13–14 km (∼360–370 K) identify the level of convective transport at the upstream source regions

Atmospheric CO2 and CH4 have been continuously measured since 2009 at Longfengshan WMO/GAW station（LFS） in China. Variations of the mole fractions, influence of long-distance transport, effects of local sources/sinks and the characteristics of synoptic scale variations have been studied based on the records from 2009 to 2013. Both the CO2 and CH4 mole fractions display increasing trends in the last five years, with growth rates of 3.1±0.02 ppm yr^-1 for CO2 and 8±0.04 ppb yr^-1（standard error, 1-σ）for CH4. In summer, the regional CO2 mole fractions are apparently lower than the Marine Boundary Layer reference, with the lowest value of.13.6±0.7 ppm in July, while the CH4 values are higher than the MBL reference, with the maximum of 139±6 ppb.From 9 to 17（Local time, LT） in summer, the atmospheric CO2 mole fractions at 10 m a.g.l. are always lower than at 80 m, with a mean difference of.1.1±0.2 ppm, indicating that the flask sampling approach deployed may underestimate the background mole fractions in summer. In winter, anthropogenic emissions dominate the regional CO2 and CH4 mole fractions. Cluster analysis of backward trajectories shows that atmospheric CO2 and CH4 at LFS are influenced by anthropogenic emissions from the southwest（Changchun and Jilin city） all year. The synoptic scale variations indicate that the northeastern China plain acts as an important source of atmospheric CO2 and CH4 in winter.

A new meteorological station (DMS) was established at the Morning Glory summit in Zhejiang Province to provide regional background information on atmospheric composition in the Yangtze River Delta (YRD) region, China. This study investigated the first carbon monoxide (CO) records at DMS from September 2020 to January 2022. The annual average concentration of CO was 233.4 ± 3.8 ppb, which exceeded the measurements recorded at the other Asian background sites. The winter CO concentration remained elevated but peaked in March in the early spring due to the combined effect of regional emissions within the YRD and transportation impacts of North China and Southeast Asia sources. The diurnal cycle had a nocturnal peak and a morning valley but with a distinct afternoon climb, as the metropolis in the YRD contributed to a local concentration enhancement. The back trajectory analysis and the Weighted Potential Sources Contribution Function (WPSCF) maps highlighted emissions from Anhui, Jiangxi, Zhejiang, and Jiangsu provinces as significant sources. Due to well-mixed air conditions and fewer anthropogenic influences, DMS records closely aligned with the CO averages derived from the Copernicus Atmospheric Monitoring Service (CAMS) covering the YRD, confirming its representativeness for regional CO levels. This study underscored DMS as a valuable station for monitoring and understanding CO spatiotemporal characteristics in the YRD region.

The research of greenhouse gases on the Tibetan Plateau is of great importance since its unique topography as the third pole of our planet and profound response on the climate change. In this study, we compared the concurrent observations of atmospheric carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) during 2010–2016 from two stations located on the Tibetan Plateau, which are Mt. Waliguan station (WLG), the only World Meteorological Organization/Global Atmosphere Watch global station in the inland of Eurasia, and Shangri‐La station, a Chinese national station (XGLL). Although both stations are located at remote area, the atmospheric CO2, CH4, and CO concentrations are frequently influenced by regional sources, especially for XGLL throughout the year and WLG in summer. Due to the unique topography and regional conditions, the atmospheric CH4 and CO at both stations display different trends with other sites in China, with higher values in summer. The atmospheric CO2, CH4, and CO at the XGLL mainly represent the conditions in regional scale. As the only World Meteorological Organization/Global Atmosphere Watch global station in the inland of Eurasia, the observation results at WLG can be used to represent the conditions on the Tibetan Plateau, but some of them are frequently influenced by the emissions from the cities located on the east or north east, and some even can be affect by emissions from the Ganges basin in autumn and winter, which should be treated with caution. By subtracting the influences of the cities, we updated the growth rate of 2.45 ± 0.02 ppm yr−1 for CO2, 8.2 ± 0.1 ppb yr−1 for CH4, and −0.4 ± 0.1 ppb yr−1 for CO, compared to the prior estimation of 2.31 ± 0.02 ppm yr−1 for CO2, 8.1 ± 0.1 ppb yr−1 for CH4, and −0.6 ± 0.1 ppb yr−1 for CO on the Tibetan Plateau. Key Points Both stations on the Tibetan Plateau are influenced by regional anthropogenic emissions The CO2, CH4, and CO at the Shangri‐La station can only represent the condition in regional scale The observation results at Mt. Waliguan station are occasionally influenced by emissions from cities, especially in summer

Mole fractions of atmospheric carbon dioxide (CO 2 ) and carbon monoxide (CO) have been continuously measured since September 2010 at the Shangri-La station (28.02 ° N, 99.73 ° E, 3580 masl) in China using a cavity ring-down spectrometer. The station is located in the remote southwest of China, and it is the only station in that region with background conditions for greenhouse gas observations. The vegetation canopy around the station is dominated by coniferous forests and mountain meadows and there is no large city (population >1 million) within a 360 km radius. Characteristics of the mole fractions, growth rates, influence of long-distance transport as well as the Weighted Potential CO Sources Contribution Function (WPSCF) were studied considering data from September 2010 to May 2014. The diurnal CO 2 variation in summer indicates a strong influence of regional terrestrial ecosystem with the maximum CO 2 value at 7:00 (local time) and the minimum in late afternoon. The highest peak-to-bottom amplitude in the diurnal cycles is in summer, with a value of 18.2±2.0 ppm. The annual growth rate of regional CO 2 is estimated to be 2.5±1.0 ppm yr −1 (1-σ), which is close to that of the Mt. Waliguan World Meteorological Organization/Global Atmosphere Watch (WMO/GAW) global station (2.2±0.8 ppm yr −1 ), that is also located at the Tibetan plateau but 900 km north. The CO mole fractions observed at Shangri-La are representative for both in large spatial scale (probably continental/subcontinental) and regional scale. The annual CO growth rate is estimated to be -2.6±0.2 ppb yr −1 (1-σ). But the CO rate of decrease in continental/subcontinental scale is apparently larger than the regional scale. From the back trajectory study, it could be seen that the atmospheric CO mole fractions at Shangri-La are subjected to transport from the Northern Africa and Southwestern Asia sectors except for summer and part of autumn. The WPSCF analysis indicates that the western and southwestern areas of the Shangri-La station (India, Myanmar and Bangladesh) may be the most important CO sources.