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Citrus microcarpa is a popular nutritious fruit that is widely cultivated in China. In recent years, many compounds with significant pharmacological activities have been isolated successfully from the pericarp of C. microcarpa. However, to date, there are no reports on the activity of C. microcarpa pericarp against root-knot nematodes. This study used the ethanolic extract from the pericarp of Hainan C. microcarpa and the impregnation method to determine its activity on J2 Meloidogyne enterolobii specimens and on single-egg hatching. The results showed that when J2 individuals were treated with 50 mg.L-1 of the extract, the lethal concentration 50 values after 24 and 48 hours were 17.124 and 8.858 mg-mL-1, respectively. The mortality rate of nematodes after 48 hours of treatment was 100%, and the inhibition rate of single-egg hatching after 24 hours was 89.29%. The ethanolic extract of C. microcarpa peels showed high inhibitory and lethal activity against the M. enterolobii. The analysis of the chemical composition of the extract revealed 28 substances with insecticidal and antibacterial effects, including lignans, flavonoids, fatty acids, organic acids, terpenoids, and imidazole. The formulas of the chemical structures and pharmacological effects of these potential insecticidal and antibacterial substances were elucidated to provide a scientific basis and a theoretical reference for the use of C. microcarpa pericarps as a raw material for the development of new, natural plant nematicides. [ABSTRACT FROM AUTHOR]

The Gasi reservoir in the Qinghai oilfield is a typical high-temperature and high-salinity reservoir, with an average temperature and average salinity of 70.0 °C and 152,144 mg/L, respectively. For over 30 years since 1990, water flooding has been the primary method for enhancing oil recovery. Recently, the Gasi reservoir has turned into a mature oilfield. It possesses a high water cut of 76% and a high total recovery rate of 47%. However, the main developing enhanced oil recovery (EOR) technology for the development of the Gasi reservoir in the next stage is yet to be determined. Surfactant–polymer (SP) flooding, which can reduce the oil–water interfacial tension and increase the viscosity of the water phase, has been widely applied to low-temperature and low-salinity reservoirs across China in the past few decades, but it has rarely been applied to high-temperature and high-salinity reservoirs such as the Gasi reservoir. In this study, the feasibility of SP flooding for high-temperature and high-salinity reservoirs was established. Thanks to the novel surfactant and polymer products, an SP flooding formula with surfactants ZC-2/B2 and polymer BRH-325 was proposed for Gasi. The formula showed a low interfacial tension of 10−2 mN/m and a high viscosity of 18 MPa·s in simulated reservoir conditions. The oil displacement experiment demonstrated that this formula can enhance the oil recovery rate by 26.95% upon water flooding at 64.64%. This study provides a feasible EOR candidate technology for high-temperature and high-salinity reservoirs, as exemplified by the Qinghai Gasi reservoir. [ABSTRACT FROM AUTHOR]

Biomass burning serves as important sources of volatile organic compounds (VOCs), yet our understanding of the molecular characteristics of oxygenated volatile organic compounds (OVOCs) from fresh emissions remains limited. In this study, gaseous organic compounds in fresh smokes from burning typical Chinese crop straws and woods are measured using an iodide time‐of‐flight chemical ionization mass spectrometer. Approximately 750 molecular formulas are identified, with CHO compounds containing carbon, hydrogen and oxygen atoms accounting for 77%–95% of the total. C1–C3 organic acids and dicarboxylic acids dominate the total CHO signal intensities by 27%–48%, while well‐known molecular markers of biomass burning, such as monosaccharide, guaiacol and syringol derivatives, contribute 7%–17%. Notably, crop straw and wood burning emit a higher abundance of guaiacol than syringol derivatives by a factor of 5. Additionally, a variety of nitrogen‐containing compounds (mainly in the CHON group) is identified, including isocyanate, amide, amino acids, and pyridine. The mass spectral profiles of organic compounds are largely similar between crop straw and wood burning fuels, although wood burning produces higher contributions of compounds with carbon atoms numbers >10. The saturation concentrations of organic compounds are estimated using molecular formula‐based volatility parameterization, revealing that semi‐volatile and intermediate VOCs (S/intermediate volatility organic compounds (IVOCs)) predominate smoke releases by 35%–60% and 20%–43%, respectively, with only a small fraction of low‐volatility compounds. Given the widespread nature of biomass burning in winter China, our results may have significant implications for interpreting secondary organic aerosol formation through gas‐particle partitioning or aqueous‐phase reactions. Plain Language Summary: Biomass burning is a significant source of volatile organic compounds (VOCs), with oxygenated volatile organic compounds (OVOCs) being particularly important due to their high reactivity and their contribution to the radical budget and secondary products formation. However, previous research has primarily focused on a limited number of OVOCs species from pine, spruce, and other biofuels, leading to insufficient studies on the full mass spectra of OVOCs from biomass smokes. Our study has addressed this gap by identifying approximately 750 OVOCs from burning typical Chinese crop straws and woods. We found that C1–C3 organic acids and dicarboxylic acids are the predominant contributors to total signal intensities. This expands on previous studies that have focused on a limited well‐known molecular markers of biomass burning, such as monosaccharide, guaiacol and syringol derivatives, and reveals the presence of nitrogen‐containing compounds, including isocyanate, amide, amino acids, and pyridine. The saturation concentrations of organic compounds are estimated, highlighting the importance of semi‐volatile and intermediate VOCs (S/IVOCs) in fresh smoke releases. Our study contributes to a better understanding of complex chemistry of biomass burning and its impact on air quality. It will serve as a crucial basis for accurately assessing biomass burning related‐secondary organic aerosol formation. Key Points: C1–C3 organic acids and dicarboxylic acids dominate the total signal intensities of fresh crop straw and wood burning emissionsThe mass spectral profiles are largely similar across different fuels, with wood burning produces higher contributions of large compoundsSemi‐volatile and intermediate volatile organic compounds predominate fresh smoke emissions, with only a small fraction of low‐volatility compounds [ABSTRACT FROM AUTHOR]

The characterization of dissolved organic matter (DOM) is important for better understanding of the migration and transformation mechanisms of DOM in water bodies and its interaction with other contaminants. In this work, fluorescence characteristics and molecular compositions of the DOM samples collected from the mainstream, tributary, and sewage outfall of the Inner Mongolia section of the Yellow River (IMYR) were determined by using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In addition, concentrations of potentially toxic elements (PTEs) in the relevant surface water and their potential relationships with DOM were investigated. The results showed that the abundance of tyrosine-like components increased significantly in downstream waters impacted by outfall effluents and was negatively correlated with the humification index (HIX). Compared to the mainstream, outfall and tributaries have a high number of molecular formulas and a higher proportion of CHOS molecular formulas. In particular, the O5S class has a relative intensity of 41.6% and the O5-7S class has more than 70%. Thirty-eight PTEs were measured in the surface water samples, and 12 found above their detective levels at all sampling sites. Protein-like components are positively correlated with Cu, which is likely indicating the source of Cu in the aquatic environment of the IMYR. Our results demonstrated that urban wastewater discharges significantly alter characteristics and compositions of DOM in the mainstream of IMYR with strongly anthropogenic features. These results and conclusions are important for understanding the role and sources of DOM in the Yellow River aquatic environment. [ABSTRACT FROM AUTHOR]

• DOMs in various farmland soils were characterized by EEM-PARAFAC and FTICR-MS. • National spatial distributions of soil DOM were investigated across mainland China. • Numerous molecular formulae were detected, covering a wide range, by 15T FTICR-MS. • The difference in DOM spatial heterogeneity was reflected in CHOS and CHONS. • Lignin and tannin contributed top proportions probably due to soil-derived humus. Dissolved organic matter (DOM) plays an essential role in many geochemical processes, however its complexity, chemical diversity, and molecular composition are poorly understood. Soil samples were collected from 500 vegetable fields in administrative regions of mainland China, of which 122 were selected for further investigation. DOM properties were characterized by three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) (field intensity is 15 Tesla). Our results indicated that the main constituents were UVA humic-like substances, humic-like substances, fulvic acid-like substances, and tyrosine-like substances. A total of 10,989 molecular formulae with a mass range of 100.04 to 799.59 Da were detected, covering the mass spectrometric information of the soil samples from 27 different regions. CHO and CHON molecules were dominant in DOM, whereas lignin, tannins, and aromatic substances served as the main components. The results of cluster analysis revealed that the soil properties in Jiangxi Province were considerably different from those in other regions. The key backgrounds of the DOM molecular characteristics in the vegetable-field soil samples across mainland China were provided at the molecular level, with large abundance and great variability. [Display omitted] [ABSTRACT FROM AUTHOR]

Atmospheric organic aerosol (OA) affects air quality and human health. However, compared with urban areas, the chemical composition and temporal distribution of OA in rural regions are still not well understood. In this study, one-year atmospheric particles with an aerodynamic equivalent diameter of ≤2.5 μm (PM2.5) were collected at a rural site in Quzhou County, the North China Plain (NCP), from August 2020 to July 2021. OA in PM2.5 samples were analyzed with an ultrahigh-performance liquid chromatograph (UHPLC) coupled to an ultrahigh-resolution Orbitrap mass spectrometer in negative mode (ESI−). The results show that the chemical composition and properties of OA varied in different seasons. According to the hierarchical cluster analysis, the molecular formulas of winter OA were close to those in spring, whereas the chemical composition of OA in summer and autumn was similar. The O/C ratio of summer OA was the highest at 1.21, followed by that in autumn (0.92) and spring (0.87), while the winter OA had the lowest O/C ratio of 0.64. It indicates that, compared to the other three seasons, OA underwent more intense oxidation processes in the summer. Moreover, winter OA contained more aromatic compounds with a relative peak abundance fraction of 40%, which may be related to anthropogenic sources (e.g., coal burning) in the winter in the NCP. In addition, biomass burning is considered an important source of OA in the rural region of Quzhou County, the NCP, in all seasons. [ABSTRACT FROM AUTHOR]

This article discusses the chemical compounds found in the leaves and stems of Aconitum carmichaelii, a traditional Chinese medicine known as "Fu-Zi." The study identifies 21 alkaloids, some of which were isolated for the first time from this plant. These compounds have potential pharmacological effects, such as analgesic and anti-inflammatory properties. The research provides valuable insights into the chemical composition of A. carmichaelii and its potential medicinal uses. The document presents technical information about the molecular formulas, physical properties, and spectroscopic data of various compounds, including oxoglaucine, laurotetanine, (+)-reticuline, (-)-N-methylcoclaurine, (+)-sebiferine, sinomenine, pallidine, nagarine A, neoline, and others. The authors acknowledge the financial support they received and express gratitude to the staff of the analytical group at the State Key Laboratory of Phytochemistry and Plant Resources in West China and the Kunming Institute of Botany Chinese Academy of Sciences for providing spectral data. [Extracted from the article]

Dissolved organic matter in seasonal snow (DOMsnow) has a noticeable effect on the carbon cycle, carbon reserve, and ecosystems globally, but its regional characteristics remain unclear owing to a lack of surface measurements. The molecular compositions, potential sources, and degrees of oxidation of DOMsnow were investigated over northeastern China. The results of quantitative analysis for DOMsnow reflect the importance of anthropogenic influence. Fourier transform‐ion cyclotron resonance‐mass spectrometry analyses indicate that most (∼71%) identified molecular formulas are consistent with terrestrial compounds and derive from underlying soil and atmospheric deposition. Microbe‐derived compounds are also important contributors (∼34%) to the DOMsnow pool. The heterogeneous distribution of DOMsnow molecules is a complex process caused by many kinds of factors. Sulfate ions, organic aerosols, longitude, and altitude explain 76.2% of the regional difference in organic components. High levels of oxidation DOMsnow molecules are found, and such high reactive molecules indicate the presence of secondary organic matter and aging processes within the snowpack. The objective of this study is to investigate the characteristics of DOMsnow in high‐latitude regions of China so that we can further understand the impacts of changes in regional processes. Plain Language Summary: Dissolved organic matter in seasonal snow (DOMsnow) has significantly influenced ecosystems in cryospheric regions globally. The purpose of this study was to investigate the molecular compositions, potential sources, and influence factors of DOMsnow in northeastern (NE) China. We found that DOMsnow content in NE China was significantly influenced by anthropogenic factors. Molecules from the terrestrial environment contributed significantly to DOMsnow through atmospheric deposition and snow‐soil exchange. In addition, we identified a significant number of molecules with high oxidation, which are critical indicators of secondary organic products in snow. Sulfate ions, organic aerosols, longitude, and altitude may also play an important role in determining the regional heterogeneity of DOMsnow molecules. The proportion of DOMsnow compounds was not significantly different, but environmental differences could explain the difference in molecular weight. [ABSTRACT FROM AUTHOR]

Due to the increasing demand for rare earth elements (REE) resources in the market and the shortage of their direct sources, the research on REE in coal fly ash (CFA) has attracted the increasing attention of scholars because of its high content of rare earth. To extract and separate REE from the leaching solution of CFA, the method of solvent extraction after acid leaching is usually adopted. In this paper, the leaching solution of coal fly ash from Panbei, south China, with an average REE content of 478 μg/g, was taken as the research object. The extracted di-2-Ethylhexyl phosphonic acid (P204) was used to explore the solvent extraction effect and mechanism. When performed with the conditions: pH value of 2.1, oil-water ratio (O/A) of 1, extraction time of 25 min, solvent concentration of 6% and temperature of 30 ℃, the extraction rates of La, Ce, Pr, Nd, and Y were 89.16%, 94.11%, 95.56%, 96.33%, and 99.80%, respectively. It was indicated that the P204 extraction system separated REE well from the aqueous phase. The structure of the extraction complex was deduced by taking yttrium as an object of analysis, and the extraction mechanism equation was determined by using the slope method. In this extraction system, the molecular formula of the complex is YCl2(HA2) and the enthalpy change (△H) is +86.68 kJ/mol, which provides theoretical guidance for the extraction of REE in industrial production. [ABSTRACT FROM AUTHOR]

• A Mesoproterozoic kerogen molecular model is established for the first time. • This kerogen is mainly short-branched chains or alicyclics rather than long chains. • This kerogen model resembles Paleozoic kerogen, yet differs from Mesozoic kerogen. In the southeastern Xuanlong sag of Northern China, the organic-rich black shale of the Mesoproterozoic Xiamaling Formation holds significant potential as a source rock. Through advanced analytical techniques including elemental analysis, 13C NMR, XPS, FTIR, and XRD, the elemental composition and chemical structure were thoroughly characterized, and the molecular structure of the Xiamaling shale kerogen was established. The 13C NMR analysis revealed the carbon composition of kerogen, indicating 75.19 % aliphatic carbon, 22.06 % aromatic carbon, and 2.75 % carbonyl carbon, with quantitative support from FTIR and XRD spectra. The dominant methylene carbons exhibited a low average methylene chain length (Cn) of 3.87, suggesting that they are primarily short-branched or alicyclic compounds rather than long straight chains. This conclusion was verified by the absence of a sharp peak at a wavenumber of 719.95 cm−1 in the FTIR spectrum. Oxygen-containing functional groups observed in 13C NMR spectra were also identified in FTIR spectra at a wavenumber range of 3500–1000 cm−1. XPS analysis indicated that nitrogen-containing groups were amino, quaternary, pyridine, and primary pyrrole groups, and sulfur existed as sulfoxide, aromatic sulfur, aliphatic sulfur, and sulfone. Finally, a relatively rational 2D molecular structure with the chemical formula of C 278 H 346 N 6 O 26 S 2 was established by comparing the predicted and experimental 13C NMR spectra. Using MD simulation, five optimized 2D molecules were combined to construct a robust 3D kerogen model with a physical density of 1.067 g/cm3. Comparatively, the aliphatic structure of the Mesoproterozoic Xiamaling kerogen model consists of some monocyclic alkanes and polycyclic saturated structures, resembling Paleozoic kerogen models but differing from Mesozoic counterparts. The constructed kerogen model addresses the gap in the Precambrian kerogen modeling and sets the stage for in-depth exploration of pyrolysis mechanisms in the future. [ABSTRACT FROM AUTHOR]

The increasing prevalence of crop-threatening root-knot nematodes (RKNs) has stimulated extensive research to discover effective nematicides. A highly focused strategy for accomplishing this is the development of biocontrol agents by a variety of soilborne microorganisms, as different bacterial metabolites have demonstrated promising nematicidal activities. In this study, we characterized the nematicidal and suppressive activity of a bacterial isolate against the agriculturally important RKN Meloidogyne incognita and the model nematode Caenorhabditis elegans, and the main M. incognita-toxic metabolite of the strain. After a preliminary screening of 22 bacterial isolates with a corrected mortality (CM) of whole-cell culture greater than 50% against C. elegans from different RKN-incident soils in China, a total of 14 isolates with CM of the supernatant of culture suspension (SCS) higher than 50% against both M. incognita and C. elegans were rescreened. An isolate with the highest CM of 86.1% and 95.0% for M. incognita and C. elegans, respectively, was further identified as the species Brevundimonas bullata via morphological examination, physiological and biochemical assays and alignment analysis of 16S rRNA gene sequences. The SCS of this strain, namely, B. bullata MB756, exhibited synchronous M. incognita killing activity along with significant detrimental effects on the growth, brood size, and locomotion of C. elegans. The effects of heat treatment, pH, inoculations, and protease K proteolysis on the CM of MB756 SCS were evaluated. A major M. incognita-toxic substance in the MB756 SCS was assayed and identified using thin-layer chromatography, column chromatography and high-performance liquid chromatography with a mass spectrometer, and it was preliminarily identified as 2-ethylhexan-1-ol, with a molecular formula of C8H18O and a molecular weight of 130.3 Da. [ABSTRACT FROM AUTHOR]

For an in-depth understanding of China's low-rank coal's organic structure and pyrolysis process, Meihuajing (MHJ) coal was typically studied. Firstly, the organic structures of MHJ coal were obtained, and its molecular model was constructed based on various physical characterizations. Then, the constructed molecular model was well verified, and the pyrolysis processes of this model under heat-up and isothermal conditions were explored using ReaxFF. The results indicated that the primary organic structure of MHJ coal was aromatic skeleton (76.03%). Naphthalene was more abundant in the aromatic skeleton than benzene and anthracene. Moreover, the chemical formula of the constructed molecular model was C 388 H 259 O 89 N 5 , which was well-validated regarding physical characterizations, thermogravimetric analysis, and ReaxFF simulations. As for pyrolysis simulation, increasing the heating rate primarily suppressed the secondary cracking reactions of tar while further raising the heating rate mainly slowed down the cracking reactions of coke. Besides, the pyrolysis process of MHJ coal was divided into three steps: the rapid cracking stage, the secondary reaction stage of tar, and the basic completion stage of pyrolysis. [Display omitted] • Low-rank MHJ coal in China's Ningxia was selected as the research object. • The organic properties of MHJ coal were obtained using XRD, XPS, 13C NMR, and FTIR. • A reliable MHJ coal molecular model was built and well-validated. • The pyrolysis mechanism of MHJ coal was clarified using TGA and ReaxFF MD. [ABSTRACT FROM AUTHOR]

Intense new particle formation (NPF) events were observed in the coastal atmosphere during algae growth and farming season at Xiangshan gulf of the east China coast. High nucleation-mode iodine concentrations measured by ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS) confirmed that the NPF events were induced by iodine species. Our study provides important information on iodine speciation, size distributions, and its role in NPF in the context of heavy air pollution in China's coastal areas. For the first time, we identified 5 inorganic iodine species, 45 organic iodine compounds (35 molecular formulas), and a group of iodide–organic adducts in aerosols. The concentrations and size distributions of iodine species down to 10 nm were measured during the iodine-induced NPF, continental NPF, and non-NPF days at the coastal site and compared to those at an inland site. The iodine in the above four aerosol sample types were characterized by iodate, aromatic iodine compounds, iodoacetic acid or iodopropenoic acid, and iodide–organic adducts, respectively. Iodide and organic iodine compounds were found in the nucleation-mode particles; however, it is still not clear whether they contributed to nucleation or just new particle growth. Wild algae, as well as farmed algae, could be an important NPF source in China's coastal areas. [ABSTRACT FROM AUTHOR]

• Seasonal variations of DOM chemistry were investigated in the Xiangshan Bay. • DOM was characterized as higher degrees of humification and aromaticity during winter. • Decreased nutrients likely activate microbial carbon pump in coastal bays. • Anthropogenic inputs substantially contribute to coastal bays across China. As the widely distributed transition zones connecting the terrestrial and marine ecosystems, coastal bays have long water retention times to reconstruct the DOM pool affecting global carbon cycling. However, we still have a limited understanding of mechanisms shaping the carbon cycling of coastal bays at regional scales. To address this issue, we combined stable carbon isotopes, ultraviolet–visible absorption, fluorescence spectroscopy, and ultrahigh-resolution mass spectrometry to investigate the spatiotemporal chemistry of dissolved organic matter (DOM) in Xiangshan Bay, a semi-enclosed, eutrophic bay in southeastern China. The DOM in Xiangshan Bay was characterized by a higher degree of humification and aromaticity during winter, whereas the inverse signature during summer. Results showed that the significant seasonal variation of DOM chemistry was mainly modulated by intense primary productivity stimulated by nutrients during summer, and other factors including sediment pore water DOM release and photochemical reactions. Additionally, based on the microbial carbon pump (MCP) hypothesis, marine microorganisms may synthesize biologically recalcitrant DOM with millennia turnover time. The efficient MCP associated with reduced nutrients probably acted as a critical factor in Xiangshan Bay, leading to the formation of additional refractory molecular formulae (carboxyl-rich alicyclic molecules) and a more recalcitrant signature of DOM during winter. Incorporated with seven other coastal bays across China, it is revealed that anthropogenic inputs substantially contributed to Chinese coastal bays. Further studies need to better constrain the biogeochemical implications of these anthropogenic inputs. More importantly, decreasing the anthropogenic input of nutrients to coastal bays may enhance their functions in long-term carbon sequestration. [ABSTRACT FROM AUTHOR]

• The main oxygen-containing functional groups in the coal structure are carbonyl, ether bonds and phenolic hydroxyl groups, and the oxygen content of the coal is low. In the aliphatic structure, the ratio of methyl group to methylene group is about 0.523. • The proportion of aromatic structure carbon atoms in the coal structure is 86%, protonated aromatic carbon and aromatic bridge carbon account for about 29%; alkyl substituted aromatic carbon accounts for about 21%; phenol or ether carbon atoms account for about 4%; and carbonyl carbon accounts for about 3%. From the ratio of aromatic bridge carbon to surrounding carbon (X B P =0.53). • The molecular formula for the constructed coal model is C 108 H 71 O 4 N, and the lattice parameters are (9.034, 11.844, 18.470) Ǻ. • The density and porosity of coal molecular model are 1.271 g/cm3 and 4.098%, respectively, which can accurately reflect the physical characteristics of coal sample. To construct a molecular model of coal and study the adsorption characteristics from the perspective of microscopic molecules, the microstructure of coal samples from Pingdingshan mining area in China was studied by means of Fourier transform infrared spectroscopy (FT-IR) and carbon-13 nuclear magnetic resonance spectroscopy (13C-NMR). The coal mainly possesses an aromatic molecular structure with f a (aromaticity), f a H and X B P (the ratio of aromatic bridge carbon to surrounding carbon) being 0.86, 0.29 and 0.54, respectively. According to the results, the aromatic structure, with a high degree of condensation, is mainly dominated by pyrene and chrysene, while the aliphatic structure is mainly composed of methyl and methylene whose ratio is about 0.52. Furthermore, it contains a small amount of oxygen-containing functional groups such as carbonyl group, phenolic hydroxyl group and ether bond. In light of the above-mentioned molecular structure characteristics, the periodic structure model of Pingdingshan coal with the molecular formula C 108 H 71 O 4 N was constructed based on molecular mechanics and molecular dynamics by using the Materials Studio software. The model has a density of 1.3 g/cm3, a porosity of 4.1% and a specific surface area of 614.5 m2/g, faithfully reflecting the structural information of coal sample. Moreover, methane isothermal adsorption curves were simulated by the model at the temperatures of 318, 333 and 348 K. The experimentally measured and simulated isothermal methane adsorption curves both exhibit an error of smaller than 5% under high pressure. The results verify rationality and accuracy of the model structure. The study provides a model basis for further research on coal on the microscopic level. [ABSTRACT FROM AUTHOR]

Residential coal combustion is a prominent source of brown carbon (BrC) aerosols, but knowledge of their molecular structures and optical absorption were limited, which have notable used in ambient BrC source identification and radiative forcing calculation. In this study, the Fourier transform–ion cyclotron resonance mass spectrometry combined with partial least squares regression analysis as well as Fourier transform infrared spectroscopy analysis were used to insight the molecular compounds and structures of BrC from anthracite and bituminous coal combustions between traditional and improved stoves. The absorption Ångström exponents (AAE) and mass absorption efficiency (MAE) values for the BrC emitted from the combinations of bituminous were both 1.2–2.5 times lower than those of anthracite, interpreting that the BrC from the anthracite emissions had greater light-absorbing capacity. In contrast, the emission factor of light absorption (EF Abs) at 365 nm for the bituminous coal combusted in the traditional stove was the highest among all the tested scenarios, which revealed that the incomplete combustion of bituminous coal could emit more BrC. It was noted that primary BrC emitted from the coal combustion with traditional stoves contains higher aromaticity groups of C–C and C＝O and higher S containing organics, whereas more aliphatic groups were found in BrC using the improved stoves. N-containing (CHON and CHONS) compounds were dominated in the total molecular formula of BrC, whereas the sum of CHON and CHO groups had high double-bond equivalent (DBE) values contributed 53.5%–87.1% to the total BrC absorption. Moreover, for CHOS, the lowest of estimated molecular absorption, DBE, and DBE/C should attribute to the non-chromophoric or weak absorptive S-containing compounds. This study supplied an effective evaluation method to compare BrC emissions and their absorption for coal combustion on regional scale. [Display omitted] • The BrC emitted from anthracite coal presented high light-absorbing capacity. • Calculated CHON and CHO compounds showed dominated light absorptions in BrC. • S-containing compounds present the less absorption of BrC. [ABSTRACT FROM AUTHOR]

• DOM sources and composition of Chinese river estuaries were first analyzed. • Most of the DOM in estuaries came from the terrigenous sources (61.6%–79.2%). • Highly unsaturated compounds are the most abundant molecular formulas in river DOM. • The contribution of sewage to Chinese riverine DOM was estimated as 16.1–17.7 Gg C/yr. • First linking the molecular composition of DOM with its source across Chinese rivers. Rivers are an important connection between terrestrial ecosystems and the ocean, and are hotspots of organic carbon transformation. Riverine dissolved organic matter (DOM) concentration and composition are sensitive to both regional and global change processes. The comparative studies on riverine DOM among different rivers, especially when it comes to seasonal changes, were critical to better constrain the river carbon cycle. In this study, we analyzed organic carbon concentration, DOM sources and composition from the estuary locations of 48 Chinese rivers using the stable isotopic analysis and Fourier transform ion cyclotron resonance mass spectrometry. Both dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations, displayed significantly higher mean values in autumn than in summer (p < 0.05). Most of the DOM in these rivers entering marginal seas in four seasons came from the terrigenous sources (60.6%-68.4%), followed by the autochthonous matters (18.6%-25.6%), and the contribution of the anthropogenic sewage ranged from 7.6% to 13.7%. The proportion contributions of terrigenous and anthropogenic sources to DOM were similar in all seasons, but the contribution of autochthonous inputs showed the highest value in autumn than other seasons (p > 0.05). Although the highly unsaturated compounds are the most abundant molecular formulas detected in all riverine DOM, the molecular composition of riverine DOM shows a large difference among seven river basins. The human activity disturbance may be one of the major reasons for DOM composition differences. The contribution of sewage discharge on Chinese riverine DOM flux could be roughly estimated as 16.11–17.74 Gg C /yr. This work seeks to provide a foundation for ongoing research of regional and global riverine carbon cycling, and put forward the method for evaluating the potential impact of human disturbances on riverine organic carbon components in Chinese rivers. [ABSTRACT FROM AUTHOR]