Miao Liang

The Meiyu season over the Yangtze–Huaihe River Basin exhibits pronounced interannual variability and directly reflects the persistence of the East Asian summer rainband. This study examined the relationship between the preceding April sea ice anomaly of the Barents–Kara seas and Meiyu length during 1979–2023 based on CN05.1 precipitation, ERA5, HadISST sea ice concentration datasets, and Indo-Pacific SST index. A statistically significant inverse relationship was identified between the interannual Meiyu Length and the preceding April Barents–Kara seas sea ice anomaly, with the strongest signal located over the core Barents–Kara seas sector and a filtered Barents–Kara seas sea ice index–Meiyu length index correlation coefficient of −0.662. Composite and regression analyses demonstrated that reduced interannual April Barents–Kara seas sea ice concentration is associated with a downstream Rossby-wave-like upper-tropospheric circulation pattern, leading to a clearer upper-level potential vorticity band and an intensified westerly jet that generates increased convergence over the Yangtze–Huaihe River Basin. Additionally, the north-low–south-high circulation contrast over the East Asian–western North Pacific sector during years with a longer Meiyu period, associated with an interannual reduction in the Barents–Kara seas sea ice index, contributes to enhanced moisture convergence and convection that drive stronger ascent over the Yangtze–Huaihe River Basin, favoring a more persistent Meiyu rainband and a longer Meiyu period.

The Asian Summer Monsoon (ASM) anticyclone provides an efficient pathway for the upward transport of anthropogenic pollutants into the upper troposphere and lower stratosphere (UTLS). However, in-situ measurements of key trace gases in the UTLS remain scarce over the Qinghai-Tibet Plateau (TP), a core region of the ASM anticyclone. In August 2019, the first AirCore observations over the northern TP were conducted, providing high-resolution vertical profiles of CH 4 , CO and N 2 O from the surface up to 22 km. Instrument and campaign details are described. Notably, enhanced concentrations of CH 4 and CO, were observed at 13-14 km when the observation site was located within the ASM anticyclone, indicating that the primary influence of deep convection occurs at this altitude. Back-trajectory analyses indicate that these enhanced layers originated from northern India, the Bay of Bengal, and southern China. On average, CH 4 and CO concentrations inside the anticyclone were 30.2 ppb and 52.5 ppb higher, respectively, than those outside. N 2 O concentrations remain relatively constant throughout the troposphere but show a sharp decline approximately 2 km above the tropopause, indicating the onset of significant stratospheric influence and a weakening of ASM anticyclone confinement at this altitude. These results demonstrate the capability of the AirCore system to resolve the fine-scale vertical strucure of trace gases, offering critical insights into the upward transport of surface pollutants to the UTLS via the TP during the ASM.

Satellite-based detection of methane (CH4) point sources is crucial in identifying and mitigating anthropogenic emissions of CH4, a potent greenhouse gas. Previous studies have indicated the presence of CH4 point source emissions from coal mines in Shanxi, China, an important source region with large CH4 emissions, but a comprehensive survey has remained elusive. This study aims to conduct a survey of CH4 point sources over Shanxi's coal mines based on observations of the Advanced HyperSpectral Imager (AHSI) on board the Gaofen-5B satellite (GF-5B/AHSI) between 2021 and 2023. The spectral shift in center wavelength and change in full-width-half-maximum (FWHM) are estimated for all spectra channels, which are used as inputs for retrieving the enhancement of column-averaged dry-air mole fraction of CH4 (ΔXCH4) using a matched-filter based algorithm. Our results show that the spectral calibration on GF-5B/AHSI reduced estimation biases of emission flux rate by up to 5.0%. We applied the flood-fill algorithm to automatically extract emission plumes from ΔXCH4 maps. We adopted the integrated mass enhancement (IME) model to estimate the emission flux rate values from each CH4 point source. Consequently, we detected CH4 point sources in 32 coal mines with 93 plume events in Shanxi province. The estimated emission flux rate ranges from 857.67 ± 207.34 kg·h-1 to 14333.02 ± 5249.32 kg·h-1. The total emission flux rate reaches 13.26 t·h-1 in Shanxi, assuming all point sources emit simultaneously. Our results show that wind speed is the dominant source of uncertainty contributing about 84.84% to the total uncertainty in emission flux rate estimation. Interestingly, we found a number of false positive detections due to solar panels that are widely spread in Shanxi. This study also evaluates the accuracy of wind fields in ECMWF ERA5 reanalysis by comparing with ground-based meteorological station. We found large discrepancy, especially in wind direction, suggesting incorporating local meteorological measurements into the study CH4 point source are important to achieve high accuracy. The study demonstrates that GF-5B/AHSI possesses capabilities for monitoring large CH4 point sources over complex surface characteristics in Shanxi.

An integrated portable, dual-channel all-fibered laser heterodyne radiometer (portable-dc-LHR) with a high spectral resolution (0.0044 cm ^-1 ) for simultaneous remote sensing of atmospheric dry-air column-averaged mole fraction of CO2 and CH4 (X _CO2 and X _CH4 ) has been developed. Sunlight is modulated by a dual-channel fiber optical switch and mixed with two laser beams, which were step-scanned across two strong absorption features centered at 1603.59 nm and 1657.39 nm, respectively. Digital lock-in amplifiers are designed to demodulate the laser heterodyne signal, while self-design interferometric devices are used to monitor laser wavelength. A forward model based on relative transmittance in a narrow band and an optimal estimation inversion algorithm are used for data inversion. The portable instrument was carried out in a field campaign in Dachaidan (Qinghai Province, China, 37.744°N, 95.342°E), together with co-located Aircore and EM27/SUN measurements, in August 2020. The retrieval uncertainties of portable-dc-LHR X _CO2 and X _CH4 are 0.9 ppm and 3.4 ppb, respectively. Comparison in X _CO2 and X _CH4 observations between portable-dc-LHR and EM27/SUN show a good agreement.

Central China has been acting as a major convergence zone for sources and sinks in China, such that the climate change studies of Central China have taken on critical significance. The Jinsha atmospheric background station refers to the sole background monitoring site in Central China. It is noteworthy that the greenhouse gas attributes of the Jinsha atmospheric background station represent the greenhouse gas conditions of Central China. The seasonal and daily variations in CO₂, CH₄, and CO in the scope of time between October 2019 to April 2021 at the station were examined in this study. The effect of meteorological conditions on greenhouse gas concentrations at the site was evaluated. Furthermore, the primary transmission origins affecting the station were identified using the backward trajectory through potential source contribution function analysis. As indicated by the results, the background concentrations at the Jinsha station in 2020 for CO₂, CH₄, and CO reached 424.1 ± 0.1 ppm, 2046.2 ± 0.6 ppb, and 324.1 ± 1.1 ppb, respectively. CO₂ varied on a daily basis with higher nighttime levels, which was affected by the boundary layer elevation, photosynthesis, and human activities. In autumn, CH₄ levels peaked under the effect of agricultural activities in Central China. However, CO₂ and CO concentrations reached the maximum in winter, majorly affected by the transmissions from the Beijing–Tianjin–Hebei region and Hubei. Under China’s comprehensive carbon neutrality, more attention should be paid to the emissions from winter heating and industrial activities in the Beijing–Tianjin–Hebei region, and effects exerted by transport in the monitoring process should be differentiated in depth.

Energy production and consumption are dominant sources of CO₂ emissions. Investigating the amount and characteristics of CO₂ emission sources can aid in reducing CO₂ emissions from energy-related sectors, which could lead to the development of advanced technologies and ideas for abatement. Cities play a significant role in CO₂ emissions, representing a distinctive unit with a specialized energy consumption structure, meteorology, economy, agriculture, forest acreage, etc. Those properties interact and influence CO₂ emissions. The city-level emission inventory is an important scientific database helping to investigate emission abatement technologies and establish control strategies. In this study, city-level CO₂ emissions and ecological absorption of China’s coldest province are quantified. In the targeted region, winter lasts for about 6 months. Sectors of industry, thermal power generation, and domestic heating are dominant contributors to the total emissions. The provincial CO₂ emissions from energy consumption increased gradually, reaching 327.61 million tons in 2019. Cities with strong industrial activities produced higher CO₂ emissions. Moreover, the targeted region is a strong agriculture province, with the largest contribution to grain production in China. The absorption of farmland and forest was quantified, at 343.91 and 69.3 million tons in 2019, respectively. The total absorption was higher than the energy-related emissions. This indicated that the targeted region would provide a considerable carbon sink, attributed to the properties of its ecological system. From 2017 onwards, small boilers (single boilers smaller than 32 steam tons) were removed, and hence the emissions were lower than the original value. This study presents the characteristics of CO₂ emissions, and reveals the co-benefit of air pollution control on CO₂ reduction.

Distinguished features of cities influence the characteristics of CH₄ emissions. A city-level emission inventory represents the characteristics of CH₄ on a smaller scale, according to the special factors in each city. A city-level emission inventory was established to reveal the characteristics and source profile of CH₄ emissions in the coldest province, which is a typical provincial cold region in northeast China. The dominant sources were identified for targeted cities. Rice cultivation, coal mining, oil and gas exploitation, and livestock are the dominant emission sectors. Emissions from other sectors, including wastewater disposal, biomass burning, landfill, etc. were also estimated. The provincial CH₄ emissions increased gradually from 2003 to 2012, up to 2993.26 Gg with an annual increase rate of 2.85%; the emissions were 2740.63 in 2020. The emissions of CH₄ in Harbin, Daqing, Jiamusi, and Hegang cities were higher than in the other nine cities, which were 337.23 Gg, 330.01 Gg, 328.55 Gg, and 307.42 Gg in 2020, respectively. Agriculture, including the rice cultivation, livestock, and biomass burning sectors contributed to 51.24–62.12% of total emissions, and the contributions increased gradually. Coal mining, oil and gas exploration, and fossil fuel combustion are energy-related sources, which contributed up to 37.91% of the total emissions, and the proportion kept decreasing to 23.87% in 2020. Furthermore, meteorological factors are especially relevant to the region, by which the differences of ambient temperature are over 60 °C (±30 °C). In the summer, CH₄ emissions from the rice cultivation, biomass burning, livestock, and landfill sectors are obviously distinct from the heating period (winter), while few differences in CH₄ emissions are found from wastewater disposal and the fossil fuel production sectors.

The importance of carbon neutrality and green development rose sharply in the post‐pandemic era in China. This study investigated the long‐term variability of atmospheric carbon dioxide (CO₂) in China using CO₂ records from Mount Waliguan (WLG), the only global station of World Meteorological Organization/Global Atmosphere Watch in Eurasia, covering a 26‐year period (1994–2019). Overall, the atmospheric CO₂ mole fraction increased continuously and steadily with a growth rate of 2.15 ± 0.01 ppm yr⁻¹ over 1994–2019 at WLG. The average CO₂ mole fraction was only 359.9 ± 0.04 ppm in 1994, but reached a historic level of 414.9 ± 0.04 ppm by 2019. The mean growth rates in city sectors (data from the city regions) were slightly higher than that in the Tibetan Plateau. The seasonal amplitude of atmospheric CO₂ at WLG was lower than those at adjacent regional stations, such as Lin'an, and Shangdianzi, but larger those at global stations Mauna Loa and Minamitorishima. Potential strong source regions moved from urban areas to the southwest region away from WLG, suggesting the potential emergence of Northern India as a strong CO₂ source region. The area of potential CO₂ sources at WLG prominently expanded with time, reflecting the effect of more intensifying anthropogenic emissions in recent decades. Although numerous measures for carbon emission reduction have already been implemented, it is clear that much work, e.g., carbon emission estimation, sources/sinks tracing, cleaner energy technologies, remains to be done in order to achieve carbon emission peak and carbon neutrality set by the Chinese government.