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Heterogeneous oxidation by gas-phase oxidants is an important chemical transformation pathway of secondary organic aerosol (SOA) and plays an important role in controlling the abundance, properties, as well as climate and health impacts of aerosols. However, our knowledge on this heterogeneous chemistry remains inadequate. In this study, the heterogeneous oxidation of α-pinene ozonolysis SOA by hydroxyl (OH) radicals was investigated under both low and high relative humidity (RH) conditions, with an emphasis on the evolution of molecular composition of SOA and its RH dependence. It is found that the heterogeneous oxidation of SOA at an OH exposure level equivalent to 12 hr of atmospheric aging leads to particle mass loss of 60% at 25% RH and 95% at 90% RH. The heterogeneous oxidation strongly changes the molecular composition of SOA. The dimer-to-monomer signal ratios increase dramatically with rising OH exposure, in particular under high RH conditions, suggesting that aerosol water stimulates the reaction of monomers with OH radicals more than that of dimers. In addition, the typical SOA tracer compounds such as pinic acid, pinonic acid, hydroxy pinonic acid and dimer esters (e.g., C 17 H 26 O 8 and C 19 H 28 O 7) have lifetimes of several hours against heterogeneous OH oxidation under typical atmospheric conditions, which highlights the need for the consideration of their heterogeneous loss in the estimation of monoterpene SOA concentrations using tracer-based methods. Our study sheds lights on the heterogeneous oxidation chemistry of monoterpene SOA and would help to understand their evolution and impacts in the atmosphere. [Display omitted] [ABSTRACT FROM AUTHOR]

In order to study the molecular weight and molecular structure changes of asphalt under ultraviolet aging and the mechanism of their effects on macro properties, gel permeation chromatography and nuclear magnetic resonance tests were carried out on four commonly used asphalt, respectively. The molecular weight composition changes, such as molecular weight and molecular relative mass distribution, and the molecular structure composition changes, such as hydrogen spectrum, carbon spectrum, hydrogen atom content and molecular structure parameters were studied. On the basis of macroscopic rheological tests, the molecular composition of asphalt rheological properties was characterized by correlation analysis, and the molecular mechanism of ultraviolet aging macroscopic properties was analyzed. The results show that ultraviolet aging causes the agglomeration of molecules in asphalt, small molecules decreases and aggregates into large molecules, and the molecular weight distribution boundary narrows gradually. From the changes of hydrogen atoms and molecular structure parameters, it can be seen that the alkyl substituents on the aromatic ring in the asphalt increase after ultraviolet aging, resulting in the increase of the volume and stability of the aromatic ring, and the increase of molecular backbone stiffness. On the macro level, the elastic properties of asphalt increase. The phase angle, rutting factor, irrecoverable compliance and recovery rate of asphalt before and after ultraviolet aging were obtained by macroscopic rheological tests. The correlation analysis shows that the rheological properties are most affected by condensation degree parameters, substitution rate of peripheral hydrogen, average molecular weight and branched degree of alkyl chain. [ABSTRACT FROM AUTHOR]

Lake Baiyangdian is one of China's largest macrophyte - derived lakes, facing severe challenges related to water quality maintenance and eutrophication prevention. Dissolved organic matter (DOM) was a huge carbon pool and its abundance, property, and transformation played important roles in the biogeochemical cycle and energy flow in lake ecosystems. In this study, Lake Baiyangdian was divided into four distinct areas: Unartificial Area (UA), Village Area (VA), Tourism Area (TA), and Breeding Area (BA). We examined the diversity of DOM properties and sources across these functional areas. Our findings reveal that DOM in this lake is predominantly composed of protein - like substances, as determined by excitation - emission matrix and parallel factor analysis (EEM - PARAFAC). Notably, the exogenous tyrosine-like component C1 showed a stronger presence in VA and BA compared to UA and TA. Ultrahigh - resolution mass spectrometry (FT - ICR MS) unveiled a similar DOM molecular composition pattern across different functional areas due to the high relative abundances of lignan compounds, suggesting that macrophytes significantly influence the material structure of DOM. DOM properties exhibited specific associations with water quality indicators in various functional areas, as indicated by the Mantel test. The connections between DOM properties and NO 3 N and NH 3 N were more pronounced in VA and BA than in UA and TA. Our results underscore the viability of using DOM as an indicator for more precise and scientific water quality management. [Display omitted] [ABSTRACT FROM AUTHOR]

Heavy oil is an important resource in current petroleum exploitation, and the chemical composition information of heavy oil is crucial for revealing its viscosity-inducing mechanism and solving practical exploitation issues. In this study, the techniques of high-temperature gas chromatography and highresolution mass spectrometry equipped with an electrospray ionization source were applied to reveal the chemical composition of typical heavy oils from western, central, and eastern China. The results indicate that these heavy oils display significant variations in their bulk properties, with initial boiling points all above 200 °C. Utilizing pre-treatment and ESI high-resolution mass spectrometry, an analysis of the molecular composition of saturated hydrocarbons, aromatic hydrocarbons, acidic oxygen compounds, sulfur compounds, basic nitrogen compounds, and neutral nitrogen compounds within the heavy oil was conducted. Ultimately, a semi-quantitative analysis of the molecular composition of the heavy oil was achieved by integrating the elemental content. The semi-quantitative analysis results of Shengli-J8 heavy oil and a conventional Shengli crude oil show that Shengli-J8 heavy oil lacks alkanes and low molecular weight aromatic hydrocarbons, which contributes to its high viscosity. Additionally, characteristic molecular sets for different heavy oils were identified based on the semi-quantitative analysis of molecular composition. The semi-quantitative analysis of molecular composition in heavy oils may provide valuable reference data for establishing theoretical models on the viscosity-inducing mechanism in heavy oils and designing viscosity-reducing agents for heavy oil exploitation. [ABSTRACT FROM AUTHOR]

The organic and inorganic composition of pyrolytic liquids derived from biomass pyrolysis and their effects on plant growth with foliar fertilization are insufficiently understood. Particularly, whether there is a link between the composition and effect on plant growth and their property of feedstock and of pyrolysis conditions remains unknown. In this study, three typical pyrolytic liquids derived from pyrolysis of apple branches, maize shoots, and rice husks were selected, the mineral elements and organic molecular composition as well as dissolvable organic carbon content were analyzed using volumetric analysis and GC-MS mass spectroscopy. Subsequently, the liquids were used to formulate liquid fertilizers with consistent amounts of major mineral nutrients (N-P2O5-K2O + DOC, 35% + 10%) . Then, a field demonstration experiment with foliar spraying on capsicum was conducted in a vegetable farm near Nanjing. The field experiment included 5 treatments of no foliar fertilizer (CK, clean water only), commercial foliar fertilizer (WSF), and foliar fertilizer with pyrolytic liquids of rice husk (RF), maize shoots (CF), and apple branches (AF) . When the capsicum was ripe, fruit yield was measured and plant samples were collected for quality assessment. The results showed that the pyrolytic liquids varied not only in organic and inorganic contents but also in organic molecule abundances. The dissolvable organic carbon pool was dominated by organic acids and phenolic compounds with varying amounts of ketones, aldehydes, and esters. In pyrolytic liquids derived from pyrolysis of apple branches and rice husks, organic acids and phenolic compounds were the most abundant, respectively. However, all liquid fertilizers with pyrolytic liquids promoted capsicum growth and improved plant quality. Among them, the AF treatment was the best, followed by CF, RF and WSF treatments. Compared with CK, all the foliar spraying treatments increased the capsicum yield (over 35% on average) and AF treatments increased by 62%. Particularly, the number of fruits, leaf area, and SPAD of a single capsicum plant was significantly increased by 54.73%, 26.99%, and 19.67%, when sprayed with fertilizers containing AF over those containing CK. Similarly, all the foliar spraying treatments increased the size of capsicum fruit (over 25%) and the content of soluble sugar and capsaicin (20% on average) as well as soluble protein (5%) . Moreover, AF treatment exerted the most significant improvement in capsicum growth and quality parameters among the studied foliar fertilizers, the content of soluble sugar, soluble protein, Vitamin C, capsaicin and dry matter were increased by 6%-30%. Overall, the effect of the pyrolytic liquids-based foliar fertilizers on capsicum plant growth and quality was related to the abundance of organic acids of low molecular weight and antioxidant phenols than to that of mineral nutrients [ABSTRACT FROM AUTHOR]

The gas sources in the eastern Cote d'Ivoire Basin (Tano Basin) are seldom reported and remain controversial due to multiple sets of potential source rocks and poorly documented geochemical characteristics of natural gases. The marine source rock potential from the Upper Albian to Turonian as well as the molecular composition and the stable carbon isotope composition of natural gases in the eastern Cote d'Ivoire Basin were studied in detail to investigate the origins of natural gases. The total organic carbon (TOC), hydrogen index (HI), and generation potential (S1 + S2) of source rocks indicate that both sapropelic source rocks and humic source rocks developed during the late Albian, whereas sapropelic source rocks developed during the Cenomanian and the Turonian. The normal order of δ13CH4 < δ13C2H6 < δ13C3H8 (δ13C1 < δ13C2 < δ13C3), the relationship between C2/C3 molar ratio and δ13C2-δ13C3, and the plot of δ13C1 versus C1/(C2+C3) collectively show that the natural gases are thermogenic due to the primary cracking of kerogen, including the typical oil-associated gases from Well D-1, the mixed oil-associated gases and coal-derived gases from Well G-1 and Well L-1. Based on the plot of δ13C1 versus δ13C2 and the established relationship between δ13C1 and equivalent vitrinite reflectance (Ro), we proposed that the natural gases are in a mature stage (Ro generally varies from 1.0% to 1.3%). Combined with results of basin modelling and oil-to-source correlation, the transitional to marine source rocks during the late Albian were thought to have made a great contribution to the natural gases. Our study will make a better understanding on petroleum system in the eastern Cote d'Ivoire Basin. [ABSTRACT FROM AUTHOR]

Identifying the unnecessary H2 consumption existing in diesel hydrotreating process and calculating theoretical minimum H2 consumption are extremely critical for reducing H2 consumption in consideration of carbon reduction and resource utilization improvement. In this work, chemical reactions happened during diesel hydrotreating were categorized into hydrodesulfurization (HDS), hydrodenitrogenation (HDN), saturation of monocyclic aromatic hydrocarbons (MAHs), saturation of polycyclic aromatic hydrocarbons (PAHs), hydrogenation of olefins (HGO) and hydrocracking reactions (HCR). Then, in order to gain insights into where and how much H2 can be reduced, the ideal molecular compositions of the products were analyzed when theoretical minimum H2 was achieved for each type of reactions, which can give a genuine value of average relative molecular weight and average number of moles of H2 consumed per mole of reactants, leading to the establishment of method for calculating theoretical minimum H2 consumption. Additionally, the above method was used to calculate theoretical minimum H2 consumption of five diesel feedstocks with different properties to study the influence of content of S, N and PAHs in the feed on theoretical minimum H2 consumption. This method can provide guidance for experiments of H2 consumption reduction, and also help the refineries to save potential costs of H2. [ABSTRACT FROM AUTHOR]

Reservoirs exert a profound influence on the cycling of dissolved organic matter (DOM) in inland waters by altering flow regimes. Biological incubations can help to disentangle the role that microbial processing plays in the DOM cycling within reservoirs. However, the complex DOM composition poses a great challenge to the analysis of such data. Here we tested if the interpretable machine learning (ML) methodologies can contribute to capturing the relationships between molecular reactivity and composition. We developed time‐specific ML models based on 7‐day and 30‐day incubations to simulate the biogeochemical processes in the Three Gorges Reservoir over shorter and longer water retention periods, respectively. Results showed that the extended water retention time likely allows the successive microbial degradation of molecules, with stochasticity exerting a non‐negligible effect on the molecular composition at the initial stage of the incubation. This study highlights the potential of ML in enhancing our interpretation of DOM dynamics over time. Plain Language Summary: As a comprehensive man‐made infrastructure, reservoirs significantly influence the chemical composition, reactivity, and turnover time of dissolved organic matter (DOM) within inland waters. However, it remains elusive how DOM molecules respond to microbial processing over different time scales. Besides the well‐recognized predictive power of machine learning (ML) methodologies, we delved into the processes of tuning the ML models to acquire additional interpretability. We used an under‐sampling strategy to improve model performance and simultaneously observed the variations in model performance metrics for different biological reactivity pools over incubations with different durations. We find that shorter incubation periods result in a broader range of molecules disappearing, with a greater contribution of stochasticity, while the longer incubation allows the successive biodegradation of oxygen‐poor compounds, with a greater contribution of directed degradation. As a complement to traditional geochemical methods, we unveiled a novel perspective in understanding the DOM dynamics over time using ML. Key Points: Machine learning (ML) models were built to correlate the molecular composition and biological reactivity at the world's largest reservoirShorter incubations result in a broader range of molecules disappearing, with a greater contribution of stochasticityTuning the ML model contributes to yield additional interpretability beyond its well‐recognized predictive power [ABSTRACT FROM AUTHOR]

Biochar, formed through the pyrolysis or burning of organic wastes, has a complex chemical composition influenced by feedstock, pyrolysis temperature, and reaction conditions. Water-soluble, dissolved black carbon species released from biochar comprise one of the most photoreactive organic matter fractions. Photodegradation of these water-soluble species from wheat straw biochar, produced at different pyrolysis temperatures in laboratory microcosms, resulted in noticeable compositional differences. This study characterized water-soluble transformation products formed through the photodegradation of wheat straw biochar pyrolyzed at 300, 400, 500, or 600°C by electrospray ionization 21 ​T Fourier transform ion cyclotron resonance mass spectrometry (21T FT-ICR MS). We also evaluated global trends in the toxicity of these water-soluble fractions using MicroTox™ to assess the impacts of pyrolysis temperature. Additionally, we examined biochar surface morphology after photodegradation and observed minimal change after irradiation for 48 ​h, though the total yield of water-soluble biochar species varied with pyrolysis temperature. Trends in toxicity observed from MicroTox® analysis reveal that water-soluble photoproducts from biochar produced at 300°C and 900°C are nearly three times as toxic compared to dark controls. The ultrahigh resolving power of 21T FT-ICR MS allows for the separation of tens of thousands of highly oxidized, low-molecular-weight (

Within the eastern part of the Fukang depression, the main productive series are confined to the Permian and Jurassic oil and gas complexes (OGC), in which the Middle Permian and Lower-Middle Jurassic oil and gas source rocks (OGSRs) are distinguished. The article discusses in detail the oil and gas source characteristics of the Middle Permian and Lower-Middle Jurassic rocks, the molecular composition of oils and bitumoids from the OGSRs, and also interprets the characteristics of the biomarkers in them from the standpoint of the sedimentary-migration theory of oil generation. An attempt is made to explain the reasons for the difference in the properties and composition of oils from different OGCs. It is shown that the composition of hydrocarbon fluids of deposits is determined not only by the geological and geochemical conditions of sedimentation of oil and gas source deposits, but also associated with migration processes and subsequent secondary changes in the accumulation. In terms of composition, three groups of oils were identified: Permian and Jurassic heavy oils with a light carbon isotopic composition and the presence of β-carotene and gammacerane, they underwent different degrees of biodegradation, which depended on the geological conditions of the deposits; Permian medium oils in density (0.84 and 0.87 g/cm3 ), the composition of biomarkers of which is very close to that of the first group, and Jurassic light oils with a high content of solid paraffins and a heavier carbon isotopic composition, almost do not contain β-carotene and gammacerane concentrations are low.

Dissolved organic matter (DOM) assemblages in freshwater rivers are formed from mixtures of simple to complex compounds that are highly variable across time and space. These mixtures largely form due to the environmental heterogeneity of river networks and the contribution of diverse allochthonous and autochthonous DOM sources. Most studies are, however, confined to local and regional scales, which precludes an understanding of how these mixtures arise at large, e.g., continental, spatial scales. The processes contributing to these mixtures are also difficult to study because of the complex interactions between various environmental factors and DOM. Here we propose the use of machine learning (ML) approaches to identify ecological processes contributing toward mixtures of DOM at a continental-scale. We related a dataset that characterized the molecular composition of DOM from river water and sediment with Fourier-transform ion cyclotron resonance mass spectrometry to explanatory physicochemical variables such as nutrient concentrations and stable water isotopes (2H and 18O). Using unsupervised ML, distinctive clusters for sediment and water samples were identified, with unique molecular compositions influenced by environmental factors like terrestrial input and microbial activity. Sediment clusters showed a higher proportion of protein-like and unclassified compounds than water clusters, while water clusters exhibited a more diversified chemical composition. We then applied a supervised ML approach, involving a two-stage use of SHapley Additive exPlanations (SHAP) values. In the first stage, SHAP values were obtained and used to identify key physicochemical variables. These parameters were employed to train models using both the default and subsequently tuned hyperparameters of the Histogram-based Gradient Boosting (HGB) algorithm. The supervised ML approach, using HGB and SHAP values, highlighted complex relationships between environmental factors and DOM diversity, in particular the existence of dams upstream, precipitation events, and other watershed characteristics were important in predicting higher chemical diversity in DOM. Our data-driven approach can now be used more generally to reveal the interplay between physical, chemical, and biological factors in determining the diversity of DOM in other ecosystems. [ABSTRACT FROM AUTHOR]

The formation process of in‐cloud aqueous‐phase secondary organic matter (aqSOM) and its characteristics are unclear. Herein, water‐soluble inorganic ions, oxalate, and water‐soluble organic carbon (WSOC) were determined in cloud water and aerosol (PM2.5) samples simultaneously collected at a remote mountain site in southern China during spring 2018 and winter 2020. The molecular compositions of water‐soluble organic matter (WSOM) in cloud water and aerosols were analyzed by a Fourier transform ion cyclotron resonance mass spectrometer in negative electrospray ionization (ESI‐) mode. The results showed that the mean concentration of WSOC was 6.27–8.54 mg C L−1 in cloud water and 0.60–1.37 μg C m−3 in aerosols. The strong correlation observed between WSOM and aqueous secondary matter (e.g., NO3− and oxalate), the positive matrix factorization results, and the elevated WSOM/K+ ratios observed in cloud water suggested enhanced aqSOM formation in cloud water. According to random forest analysis, the factors related to in‐cloud WSOM variation mainly included secondary ions, K+, cloud water pH, and atmospheric NOx. Additionally, 37 characteristic in‐cloud aqSOM molecules, classified as ‐Ox, ‐NOx, ‐N2Ox, and ‐N1‐2OxS, mainly consisting of dicarboxylic acids, nitrophenols, and dinitrophenols, were identified using linear discriminant analysis effect size (LefSe). The characteristic N‐ and S‐containing molecules in in‐cloud aqSOM with carbon numbers >10 had low or extremely low volatility; therefore, they might contribute to secondary organic aerosol formation after droplet evaporation. The results revealed the modifying effects of in‐cloud processes on aerosol organic composition at the molecular level and could improve our understanding of aerosol–cloud interactions. Plain Language Summary: In this study, we determined the water‐soluble ion, water‐soluble organic matter (WSOM) and organic molecular composition of cloud water and aerosol samples collected at a remote mountain site in southern China. The results indicated the formation of secondary organic matter (SOM) in cloud water, the proportion of which in total WSOM was >50%. In addition, the characteristic molecules of SOM in cloud water were identified, some of which had low or extremely low volatility and might remain in the particulate phase after droplet evaporation. This work advanced our understanding of secondary organic aerosol formation in cloud water and its implications for the climate and the environment. Key Points: The proportion of in‐cloud aqueous‐phase secondary organic matter in WSOM was >50%Some molecules, for example, diacids and dinitrophenols, were identified as characteristic molecules of in‐cloud secondary organic matterMolecules with C numbers >10 formed by in‐cloud processes had low volatility [ABSTRACT FROM AUTHOR]

Although mangrove forests occupy only 0.5% of the global coastal area, they account for 10–15% of coastal organic carbon (OC) storage, and 49–98% of OC is stored in sediments. The biogeochemistry of iron minerals and OC in marine sediments is closely related. To better reveal the role of iron minerals in OC preservation in mangrove sediments, an established dithionite–citrate–bicarbonate (DCB) extraction method was used to extract iron-bound OC (Fe-OC), and then the parameters of OC, Fe-OC, iron content, carbon isotopes, infrared spectroscopy, and XRD diffractions of sediments at a 1 m depth in four typical mangrove communities in the Gaoqiao Mangrove Reserve, Guangdong, China, were systematically measured. XRD diffractograms showed that the iron minerals in mangrove sediments may mainly exist in the form of goethite, which is consistent with the predominant types of iron minerals in marine sediments. About 10% of OC is directly bound to iron, and it is further estimated that about 2.4 × 1012–3.8 × 1012 g OC is preserved in global mangrove forests each year based on the high burial rate of OC in mangrove sediments. Lower Fe-OC/OC molar ratios indicated that iron mainly binds to OC via adsorption mechanisms. More depleted δ13CFe-OC relative to δ13Cbulk indicated that iron minerals are mainly associated with terrigenous OM, and the infrared spectra also revealed that iron minerals preferentially bind to terrigenous aromatic carbon. This work supports the "giant rusty sponge" view, elucidating that iron plays an important role in the preservation of OC in mangrove sediments. [ABSTRACT FROM AUTHOR]

The composition of biomarkers of the Upper Jurassic rocks in the Vostochno-Payduginskaya exploration well of the section of the Maryanovskaya and Naunaksk formations was investigated. The conditions of organic matter (OM) sedimentation were characterized based on data on the hydrocarbon composition, namely, the distribution of normal and isoprenoid alkanes, phenanthrenes, steranes, hopanes, and alicyclic and aromatic hydrocarbons. It was found out that OM was deposited throughout the section under study under oxidizing conditions. The sediments of the Naunaksk formation were formed in a shallow basin uncontaminated with hydrogen sulfide, while the OM of the Maryanovsk formation was formed in a lacustrine environment. The presence of low concentrations of gammacerane in the Maryanovsk formation and the lower parts of the Naunaksk formation indicated weakly saline waters of the sedimentation basin in this period. The participation of higher plants in the formation of the OM composition of the Naunaksk rocks was evidenced by high concentrations of cadalene and retene and the presence of simonellite and C25 and C27n‑alkanes. [ABSTRACT FROM AUTHOR]

Abstract Dissolved organic matter (DOM) occupies a huge and uncharted molecular space. Given its properties, DOM can be presented as a promising biotechnological resource. However, research into bioactivities of DOM is still in early stages. In this study, the biotechnological potential of terrestrial and marine DOM, its molecular composition and their relationships are investigated. Samples were screened for their in vitro antibacterial, antifungal, anticancer and antioxidant activities. Antibacterial activity was detected against Staphylococcus aureus in almost all DOM samples, with freshwater DOM showing the lowest IC50 values. Most samples also inhibited Staphylococcus epidermidis, and four DOM extracts showed up to fourfold higher potency than the reference drug. Antifungal activity was limited to only porewater DOM towards human dermatophyte Trichophyton rubrum. No significant in vitro anticancer activity was observed. Low antioxidant potential was exerted. The molecular characterization by FT-ICR MS allowed a broad compositional overview. Three main distinguished groups have been identified by PCoA analyses. Antibacterial activities are related to high aromaticity content and highly-unsaturated molecular formulae (O-poor). Antifungal effect is correlated with highly-unsaturated molecular formulae (O-rich). Antioxidant activity is positively related to the presence of double bonds and polyphenols. This study evidenced for the first time antibacterial and antifungal activity in DOM with potential applications in cosmeceutical, pharmaceutical and aquaculture industry. The lack of cytotoxicity and the almost unlimited presence of this organic material may open new avenues in future marine bioprospecting efforts. Graphical abstract

Dissolved organic matter (DOM) assemblages in freshwater rivers are formed from mixtures of simple to complex compounds that are highly variable across time and space. These mixtures largely form due to the environmental heterogeneity of river networks and the contribution of diverse allochthonous and autochthonous DOM sources. Most studies are, however, confined to local and regional scales, which precludes an understanding of how these mixtures arise at large, e.g., continental, spatial scales. The processes contributing to these mixtures are also difficult to study because of the complex interactions between various environmental factors and DOM. Here we propose the use of machine learning (ML) approaches to identify ecological processes contributing toward mixtures of DOM at a continental-scale. We related a dataset that characterized the molecular composition of DOM from river water and sediment with Fourier-transform ion cyclotron resonance mass spectrometry to explanatory physicochemical variables such as nutrient concentrations and stable water isotopes (2H and 18O). Using unsupervised ML, distinctive clusters for sediment and water samples were identified, with unique molecular compositions influenced by environmental factors like terrestrial input and microbial activity. Sediment clusters showed a higher proportion of protein-like and unclassified compounds than water clusters, while water clusters exhibited a more diversified chemical composition. We then applied a supervised ML approach, involving a two-stage use of SHapley Additive exPlanations (SHAP) values. In the first stage, SHAP values were obtained and used to identify key physicochemical variables. These parameters were employed to train models using both the default and subsequently tuned hyperparameters of the Histogram-based Gradient Boosting (HGB) algorithm. The supervised ML approach, using HGB and SHAP values, highlighted complex relationships between environmental factors and DOM diversity, in particular the existence of dams upstream, precipitation events, and other watershed characteristics were important in predicting higher chemical diversity in DOM. Our data-driven approach can now be used more generally to reveal the interplay between physical, chemical, and biological factors in determining the diversity of DOM in other ecosystems.

Recently, extreme wildfires occur frequently around the world and emit substantial brown carbon (BrC) into the atmosphere, whereas the molecular compositions and photochemical evolution of BrC remain poorly understood. In this work, primary smoke aerosols were generated from wood smoldering, and secondary smoke aerosols were formed by the OH radical photooxidation in an oxidation flow reactor, where both primary and secondary smoke samples were collected on filters. After solvent extraction of filter samples, the molecular composition of dissolved organic carbon (DOC) was determined by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). The molecular composition of dissolved BrC was obtained based on the constraints of DOC formulae. The proportion of dissolved BrC fractions accounted for approximately 1/3–1/2 molecular formulae of DOC. The molecular characteristics of dissolved BrC showed higher levels of carbon oxidation state, double bond equivalents, and modified aromaticity index than those of DOC, indicating that dissolved BrC fractions were a class of organic structures with relatively higher oxidation state, unsaturated and aromatic degree in DOC fractions. The comparative analysis suggested that aliphatic and olefinic structures dominated DOC fractions (contributing to 70.1%-76.9%), while olefinic, aromatic, and condensed aromatic structures dominated dissolved BrC fractions (contributing to 97.5%-99.9%). It is worth noting that dissolved BrC fractions only contained carboxylic-rich alicyclic molecules (CRAMs)-like structures, unsaturated hydrocarbons, aromatic structures, and highly oxygenated compounds. CRAMs-like structures were the most abundant species in both DOC and dissolved BrC fractions. Nevertheless, the specific molecular characteristics for DOC and dissolved BrC fractions varied with subgroups after aging. The results highlight the similarities and differences in the molecular compositions and characteristics of DOC and dissolved BrC fractions with aging. This work will provide insights into understanding the molecular composition of DOC and dissolved BrC in smoke.

Mountain ecosystems exhibit rapid changes in vegetation cover and climate conditions along elevation gradients, offering an ideal natural experiment to examine variations in the molecular composition of soil organic carbon (SOC) responsing to environmental change. We examined molecular composition, diversity, and network complexity of SOC using the pyrolysis-gas chromatography/mass spectrometry technology and the Shannon diversity index (SHDI) in Changbai Mountain (CBS). Results indicated that molecular composition of SOC differed greatly across different vegetation zones, which were predominated by mixed coniferous and broad-leaved forests (HJL), mixed coniferous forests (ZYL), birch forest covered (YHL), and tundra vegetation (TYD). ZYL had remarkably more abundant moieties with aromatic structures, 36% on average, than those in HJL, TYD, and YHL, 18.31%, 12.75% and 16.51% on average, respectively. O-alkyl, alkyl, and terpene compounds showed an increasing trend, whereas aromatic, lignin and nitrogen-containing compounds exhibited a notable decrease with elevation to a significant level. Either alpha diversity or beta diversity of SOC varied significantly among TYD, YHL, ZYL, and HJL, with HJL exhibiting the lowest alpha diversity. SOC from ZYL was the most complex, showing the highest number of edges and graph density. Leaf litter elements greatly regulated the molecular diversity and network complexity of SOC. Positive correlations between SHDI and SOC contents, as well as ratios of SOC to total iron, suggested that high molecular diversity promoted SOC persistence in mountain ecosystems.

In recent years, the problems associated with continuous cropping (CC) that cause soil degradation have become increasingly serious. As a key soil quality property, dissolved organic matter (DOM) affects the circulation of carbon and nutrients and the composition of bacterial communities in soil. However, research on the changes in the molecular composition of DOM after CC is limited. In this study, the soil chemical properties, DOM chemical diversity, bacterial community structure, and their interactions are explored in the soil samples from different CC years (CC1Y, CC3Y, CC5Y, and CC7Y) of tobacco. With increasing CC year of tobacco, most of the soil chemical properties, such as total carbon, total nitrogen and organic matter, decreased significantly, while dissolved organic carbon first decreased and then increased. Likewise, the trends of DOM composition differed with changing duration of CC, such as the tannin compounds decreased from 18.13 to 13.95%, aliphatic/proteins increased from 2.73 to 8.85%. After 7years of CC, the soil preferentially produced compounds with either high H/C ratios (H/C> 1.5), including carbohydrates, lipids, and aliphatic/proteins, or low O/C ratios (O/C< 0.1), such as unsaturated hydrocarbons. Furthermore, core microorganisms, including Nocardioides, wb1-P19, Aquabacterium, Methylobacter, and Thiobacillus, were identified. Network analysis further indicated that in response to CC, Methylobacter and Thiobacillus were correlated with the microbial degradation and transformation of DOM. These findings will improve our understanding of the interactions between microbial community and DOM in continuous cropping soil. [ABSTRACT FROM AUTHOR]

Nitrogen-containing organic compounds (NOCs) are abundant and important aerosol components, deeply involving in global nitrogen cycle. However, the sources and formation processes of NOCs remain largely unknown, particularly in the city (Urumqi, China) farthest from the ocean worldwide. Here, NOCs in PM2.5 collected in Urumqi over a one-year period were characterized by ultrahigh-resolution mass spectrometry. The abundance of CHON compounds (mainly poor-O unsaturated aliphatic-like species) in the positive ion mode was higher in the warm period than in the cold period, which was largely attributed to the contribution of fresh biomass material combustion (e.g., forest fires) associated with amidation of unsaturated fatty acids in the warm period, rather than the oxidation processes. However, CHON compounds (mainly nitro-aromatic species) in the negative ion mode increased significantly in the cold period, which was tightly related to old-age biomass combustion (e.g., dry straws) in wintertime Urumqi. For CHN compounds, we found that alkyl nitriles and aromatic CNH compounds showed higher abundance in the warm and cold periods, respectively. It further confirmed different impacts of the combustion of fresh- and old-age biomass materials on NOC compositions. Our results clarify the mechanisms by which fresh and old-age biomass materials emitted different NOCs. [ABSTRACT FROM AUTHOR]

Investigating the characteristics and transformation of water-soluble carbonaceous matter in the cryosphere regions is important for understanding biogeochemical process in the earth system. Water-soluble carbonaceous matter is a heterogeneous mixture of organic compounds that is soluble in aquatic environments. Despite its importance, we still lack systematic understanding for dissolved organic carbon (DOC) in several aspects including exact chemical composition and physical interactions with microorganisms, glacier meltwater. This review presents the chemical composition and physical properties of glacier DOC deposited through anthropogenic emission, terrestrial, and biogenic sources. We present the molecular composition of DOC and its effect over snow albedo and associated radiative forcings. Results indicate that DOC in snow/ice is made up of aromatic protein-like species, fulvic acid-like materials, and humic acid-like materials. Light-absorbing impurities in surface snow and glacier ice cause considerable albedo reduction and the associated radiative forcing is definitely positive. Water-soluble carbonaceous matter dominated the carbon transport in the high-altitude glacial area. Owing to prevailing global warming and projected increase in carbon emission, the glacial DOC is expected to release, which will have strong underlying impacts on cryosphere ecosystem. The results of this work have profound implications for better understanding the carbon cycle in high altitude cryosphere regions. A new compilation of globally distributed work is required, including large-scale measurements of glacial DOC over high-altitude cryosphere regions, to overcome and address the scientific challenges to constrain climate impacts of light-absorbing impurities related processes in Earth system and climate models. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) affects the function of terrestrial ecosystem and plays a vital role in global carbon cycle. Yet, large uncertainty still existed regarding the changes in SOC stock and quality with forest succession. Here, the stock and quality of SOC at 1-m soil profile were investigated across a subalpine forest series, including shrub, deciduous broad-leaved forest, broadleaf-conifer mixed forest, middle-age coniferous forest and mature coniferous forest, which located at southeast of Tibetan Plateau. The results showed that SOC stock ranged from 9.8 to 29.9 kg•m-2, and exhibited a hump-shaped response pattern across the forest successional series. The highest and lowest SOC stock was observed in the mixed forest and shrub forest, respectively. The SOC stock had no significant relationships with soil temperature and litter stock, but was positively correlated with wood debris stock. Meanwhile, the average percentages of polysaccharides, lignins, aromatics and aliphatics based on FTIR spectroscopy were 79.89%, 0.94%, 18.87% and 0.29%, respectively. Furthermore, the percentage of polysaccharides exhibited an increasing pattern across the forest successional series except for the sudden decreasing in the mixed forest, while the proportions of lignins, aromatics and aliphatics exhibited a decreasing pattern across the forest successional series except for the sudden increasing in the mixed forest. Consequently, the humification indices (HIs) were highest in the mixed forest compared to the other four successional stages, which means that the SOC quality in mixed forest was worse than other successional stages. In addition, the SOC stock, recalcitrant fractions and HIs decreased with increasing soil depth, while the polysaccharides exhibited an increasing pattern. These findings demonstrate that the mixed forest had higher SOC stock and worse SOC quality than other successional stages. The high proportion of SOC stock (66% at depth of 20-100 cm) and better SOC quality (lower HIs) indicate that deep soil have tremendous potential to store SOC and needs more attention under global change. [ABSTRACT FROM AUTHOR]

Marine dissolved organic matter (DOM) is a major global carbon pool, consisting of thousands of compounds with distinct lifetimes. While marine DOM persists for millennia, its molecular and isotopic composition imply that it is dynamic on shorter timescales. To determine the extent to which DOM deviates from conservative water mass mixing, we conducted a two‐endmember mixing analysis on dissolved organic carbon (DOC) concentration and DOM molecular composition in the Atlantic and Pacific. Endmembers were the deep water masses near their formation sites. For DOM composition, we considered 6118 molecular formulae (MF) identified via Fourier‐transform ion cyclotron resonance mass spectrometry in solid‐phase extracts (SPE) of 837 samples. Bulk DOC and SPE‐DOC concentrations behaved conservatively in both basins and ≥70% of the MF (14–20 μM SPE‐DOC) mixed conservatively. However, a small fraction (10%–20%) of the MF (<3 μM SPE‐DOC) were added or removed during mixing. These MF were more reduced and oxidized, respectively, than the conservative fraction. There were also MF absent from the endmembers; these accounted for ≤1 μM of SPE‐DOC and positively correlated with DOM lability. Based on their distribution across the two basins, we conclude that the conserved MF are formed in the surface subtropical ocean and modified in overturning areas. In the deep ocean, however, these MF are solely controlled by mixing. This finding contrasts with the current paradigm of slow, continuous degradation of recalcitrant DOM in the deep ocean. Our analysis illustrates the importance of the surface ocean in controlling DOM cycling in the deep. Key Points: 70% of the molecular composition of dissolved organic matter (DOM) follows two‐endmember water mass mixing in the deep Atlantic and PacificThere are small fractions of DOM with distinct chemical compositions that are added and removed relative to mixingMolecular formulae that behave conservatively in the deep are formed in the surface ocean and modified in overturning zones [ABSTRACT FROM AUTHOR]

Surfactant‐free microemulsions (SFMEs) cleaning technology can effectively separate and recover petroleum pollutants from oil‐based drilling cuttings (OBDCs). The identification of the molecular composition of OBDCs is helpful to accurately grasp the conversion mechanism of organic matter. Therefore, the understanding of the mechanism of petroleum removal at the microscopic molecular level in the cleaning process needs to be further studied. The conversion mechanism of organic matter during the use of SFMEs to clean OBDCs was investigated by positive ion atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (+APPI FT‐ICR MS). The results show that the SFMEs cleaning technology can separate and recover CH and CHO organic matter in OBDCs, but there is still a small amount of organic matter with high molecular weight and unsaturated degree in OBDCs that has not been separated. The majority of this organic matter is CH, accounting for 91 %, and it is mainly polycyclic aromatic hydrocarbons. A total of 255 kinds of organic matter in 110# industrial white oil were detected in the recovered oil after treatment, accounting for more than 99 % of the total, which has a certain recoverable value. This study can provide a theoretical reference for the efficient degradation of OBDCs. [ABSTRACT FROM AUTHOR]

Low-temperature oxidation (LTO) is the main reaction that affects fuel formation in the in-situ combustion process, which has important significance for the subsequent combustion propulsion and the successful extraction of crude oil. In this study, heavy oil was subjected to LTO reactions at different temperatures. Three types of reaction products with varying oxidation depths were characterized in terms of the number of oxygen atoms and the polarity of the molecule to reveal the low-temperature oxidation process of the heavy oil. Ketone compounds and acid polyoxides in the oil phase and deep oxidation products with a higher number of oxygen atoms in the coke were identified with increasing oxidation depth. The experimental results showed that the oxidation reaction of the heavy oil changed from kinetic-controlled to diffusion-controlled in the open oxidation system of the heavy oil as the oxidation depth increased. The oxidation reaction of the oil phase reached a maximum and stable value in oxygen content. The molecular compositions of the ketone compound and acid polyoxide did not change significantly with further increase in reaction temperature. The molecular compositions of the deep oxidation products with a higher number of oxygen atoms in the coke phase changed significantly. The coke precursor molecules with a lower oxygen content and condensation degree participated in the coke formation, and the oxidation reaction pathway and the complexity of the oxidation product component also increased. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) occupies a huge and uncharted molecular space. Given its properties, DOM can be presented as a promising biotechnological resource. However, research into bioactivities of DOM is still in early stages. In this study, the biotechnological potential of terrestrial and marine DOM, its molecular composition and their relationships are investigated. Samples were screened for their in vitro antibacterial, antifungal, anticancer and antioxidant activities. Antibacterial activity was detected against Staphylococcusaureus in almost all DOM samples, with freshwater DOM showing the lowest IC50 values. Most samples also inhibited Staphylococcusepidermidis, and four DOM extracts showed up to fourfold higher potency than the reference drug. Antifungal activity was limited to only porewater DOM towards human dermatophyte Trichophytonrubrum. No significant in vitro anticancer activity was observed. Low antioxidant potential was exerted. The molecular characterization by FT-ICR MS allowed a broad compositional overview. Three main distinguished groups have been identified by PCoA analyses. Antibacterial activities are related to high aromaticity content and highly-unsaturated molecular formulae (O-poor). Antifungal effect is correlated with highly-unsaturated molecular formulae (O-rich). Antioxidant activity is positively related to the presence of double bonds and polyphenols. This study evidenced for the first time antibacterial and antifungal activity in DOM with potential applications in cosmeceutical, pharmaceutical and aquaculture industry. The lack of cytotoxicity and the almost unlimited presence of this organic material may open new avenues in future marine bioprospecting efforts. [ABSTRACT FROM AUTHOR]

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