Organic Formation Research Articles

Simulation of Secondary Organic Aerosol Formation Using Near-Explicitly Predicted Products from Naphthalene Photooxidation in the Presence of NOx

Simulation of Secondary Organic Aerosol Formation Using Near-Explicitly Predicted Products from Naphthalene Photooxidation in the Presence of NO_<i>x</i>

Simulated nitrogen deposition and precipitation events alter microbial carbon cycling during early stages of litter decomposition

Abstract Plant litter decomposition is a major nutrient input to terrestrial ecosystems that is primarily driven by microorganisms. Litter quality is considered a key drive of decomposition; however, human-induced global disturbance like nitrogen deposition and increasing extreme precipitation events will shift nutrient availability during litter decomposition. Little is known about how shifting nutrient availability will impact dissolved organic matter concentrations and microbially driven carbon cycling that are critical to soil organic matter formation. This study investigated the effect of simulated nitrogen deposition and repeated precipitation events on microbially-driven carbon flow during short-term litter decomposition using a ‘common garden’ experiment with microcosms containing sand and blue grama grass litter inoculated with different microbial communities. Overall, nitrogen deposition decoupled respiration and dissolved organic carbon (DOC) by increasing respiration and not affecting DOC concentrations. Moreover, nitrogen deposition had no effect on microbial carbon use efficiency (CUE). Repeated simulated precipitation events significantly increased DOC concentrations, decreased microbial CUE, increased the microbial metabolic quotient (qCO2), and altered microbial composition and diversity. These findings highlight the complex interactions and responses of surface litter decomposers to shifting nutrient availability and contradicts previous findings that nitrogen deposition will increase soil carbon sequestration from a larger supply of DOC and reduced respiration.

Preclinical safety and efficacy evaluation of the intrathecal transplantation of GMP-grade human umbilical cord mesenchymal stem cells for ischemic stroke

Intrathecal administration of human umbilical cord mesenchymal stem cells may be a promising approach for the treatment of stroke, but its safety, effectiveness, and mechanism remain to be elucidated. In this study, good manufacturing practice–grade human umbilical cord mesenchymal stem cells (5 × 105 and 1 × 106 cells) and saline were administered by cerebellomedullary cistern injection 72 hours after stroke induced by middle cerebral artery occlusion in rats. The results showed (1) no significant difference in mortality or general conditions among the three groups. There was no abnormal differentiation or tumor formation in various organs of rats in any group. (2) Compared with saline-treated animals, those treated with human umbilical cord mesenchymal stem cells showed significant functional recovery and reduced infarct volume, with no significant differences between different human umbilical cord mesenchymal stem cell doses. (3) Human umbilical cord mesenchymal stem cells were found in the ischemic brain after 14 and 28 days of follow-up, and the number of positive cells significantly decreased over time. (4) Neuronal nuclei expression in the human umbilical cord mesenchymal stem cell group was greater than that in the saline group, while glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 expression levels decreased. (5) Human umbilical cord mesenchymal stem cell treatment increased the number of CD31+ microvessels and doublecortin-positive cells after ischemic stroke. Human umbilical cord mesenchymal stem cells also upregulated the expression of CD31+/Ki67+. (6) At 14 days after intrathecal administration, brain-derived neurotrophic factor expression in the peri-infarct area and the concentrations of brain-derived neurotrophic factor in the cerebrospinal fluid in both human umbilical cord mesenchymal stem cell groups were significantly greater than those in the saline group and persisted until the 28th day. Taken together, these results indicate that the intrathecal administration of human umbilical cord mesenchymal stem cells via cerebellomedullary cistern injection is safe and effective for the treatment of ischemic stroke in rats. The mechanisms may include alleviating the local inflammatory response in the peri-infarct region, promoting neurogenesis and angiogenesis, and enhancing the production of neurotrophic factors.

Amplified Secondary Organic Aerosol Formation Induced by Anthropogenic–Biogenic Interactions in Forests Around Megacities

AbstractThe amplification effect of anthropogenic‐biogenic interactions on secondary organic aerosol (SOA) formation remains debated, particularly regarding the impact of anthropogenic emissions on biogenic SOA (BSOA) formation in forests near megacities. This study concurrently measured typical biogenic and anthropogenic SOA tracers during day and night at the summit (1,690 m a.s.l.) and foot (200 m a.s.l.) of the Nanling mountains, a large subtropical forest adjacent to the Pearl River Delta (PRD) in southern China. Results revealed unexpectedly high concentrations of BSOA tracers (149.9 ± 70.5 ng m−3 at the summit and 109.7 ± 51.2 ng m−3 at the foot), surpassing those at most other background sites worldwide. Daytime BSOA tracer levels at the foot were consistent with nighttime levels, whereas the summit showed significantly higher concentrations at night. Nighttime correlations between O₃ and BSOA tracers at the summit suggest that high O₃ levels stimulate BSOA formation. Conversely, a negative correlation between O₃ and isoprene derived SOA (SOAI) tracers at the foot indicates that other oxidants may also influence SOAI formation. BSOA tracer concentrations rose significantly with the arrival of anthropogenic pollutants (e.g., SO₂ and NO₂), indicating that anthropogenic pollution amplifies BSOA formation by enhancing aerosol acidity (pH &lt; 3). This amplification effect could be mitigated by the reduction of aerosol acidity due to increased NH₃ and relative humidity (RH). Our findings provide valuable insights into the interactions between anthropogenic and biogenic emissions on SOA formation and vertical distribution in forests surrounding megacities.

Soil microbial carbon use efficiency and the constraints

Abstract Background Microbial contributions to soil organic carbon formation have received increasing attention, and microbial carbon use efficiency is positively correlated with soil organic carbon storage. Mainbody This work reviews the impact on microbial carbon use efficiency from six constraints, including plant community composition and diversity, soil pH, substrate quality, nutrient availability and stoichiometric ratios, soil texture and aggregates, water and thermal constraints, and external nutrient inputs. In general, the response of microbial carbon use efficiency showed large uncertainty to above constraints, including positive-, negative-, or non-correlation. However, some factors are biased, more likely to promote or inhibit carbon use efficiency. For example, external nutrient input (N, P, K, Ca) tended to promote carbon use efficiency, while climate warming showed more negative influence. Conclusion Further, overwhelming works focused on single constraint, we suggest the importance to consider the synergistic influence of multiple environmental variables on microbial carbon use efficiency, special for the regulation mechanism of biological-environmental interactions.

Learning Collective Cell Migratory Dynamics from a Static Snapshot with Graph Neural Networks

Multicellular self-assembly into functional structures is a dynamic process that is critical in the development of biological structures and diseases, including embryo development, organ formation, tumor invasion, and other processes. Being able to infer collective cell migratory dynamics from their static configuration is valuable for both understanding and predicting these complex behaviors. However, the identification of structural features that can indicate multicellular motion has been difficult, and existing metrics largely rely on physical instincts. Here we show that, through the use of a graph neural network, the motion of multicellular collectives can be inferred from a static snapshot of cell positions, in both experimental and synthetic datasets. Published by the American Physical Society 2024

Forming Shared Interest Pods: Barriers to Self-Assembly of Interest-Based Small Groups, and Dynamics of Retaining and Giving up Control to Find Collective Fit

We explore the challenges individuals face when seeking like-minded partners to pursue shared interests in small groups, specifically outside the workplace, classroom, or other externally organized contexts. Conducting nine 90-minute semi-structured interviews involving a hypothetical small group formation process, we found four compounding challenges that make it difficult to form and maintain stable groups. In contrast to other kinds of small groups discussed in the literature, the unique "combination" of these challenges bring into focus a class of interest-based small groups we term " shared interest pods ": self-assembled small groups united by shared interests, whose members derive benefits from sustained, synchronous interactions that hinge on the level of fit among them. The need to discover and maintain collective fit, the considerable commitment required for regular interactions, their small size, and the lack of external enforcement, makes shared interest pods fragile and unstable, and an information-rich site for studying dynamics of self-organized consensus-seeking in underexplored areas of Lee and Paine's Model of Coordinated Action, and for considering the tension between supporting personal agency through organic group formation and optimizing stability through algorithmic assignments. A central finding is how dynamics of maintaining and giving up control co-exist in shared interest pods in their search for collective fit. People seek to maintain control over certain aspects of finding fit (e.g. in determining group membership), but are simultaneously willing to give up control to organizers or algorithms under certain conditions (e.g. when balancing desired quality with social and ethical considerations). We discuss design implications for supporting the formation of shared interest pods, and more broadly, for exploring self-organized consensus-seeking in other societal collective decision-making contexts.

Concerning Toxic Byproducts and Full-Scale UV/Chlorine Advanced Oxidation Water Treatment.

This work investigated byproduct formation and in vitro genotoxicity and cytotoxicity at four facilities using UV/chlorine advanced oxidation for potable reuse or drinking water treatment. In arguably the most common application of UV/chlorine, treating reverse osmosis permeate for potable reuse, organic byproduct formation was always either not detected or well-below typical drinking water levels. At a groundwater-source drinking water treatment plant, the trihalomethanes and haloacetic acids each increased by up to 12 μg/L through the UV reactor and 40 μg/L during secondary disinfection, but the final concentrations remained low relative to regulatory limits. Overall, and aside from the known pathways of chlorate formation, the UV/chlorine byproduct and in vitro toxicity formation observed in this study was lower than what is generally found in many chlor(am)inated drinking waters, although there was some observed shift to more brominated species, which might be deserving of future research, given their higher in vitro toxicity compared to typical chlorinated species.

Soil moisture determines the consistency of organic matter decomposition in field and lab test patterns

Litter decomposition serves as the primary process for soil organic matter formation and renewal. However, few studies have been conducted to validate field large-scale litter decomposition patterns. In this study, cotton strips and Solanum nigrum were used to explore the decomposition differences between standardized litter and conventional litter, along with the release of heavy metal Cadmium (Cd). The indoor characteristics of organic matter decomposition were further verified. After 6 months of Cd pretreatment, litter was placed on the surface of soil collected from 15 sites across the China for 3 months of lab tests. The results indicated that the decomposition rates of both litter types were regulated by soil moisture and generally showed a trend of deceleration from east to west, consistent with the field decomposition pattern. In addition, the mass loss of cotton strip was significantly lower than S. nigrum due to the higher Cd concentration. With the decomposition process, both litter types showed a decreasing trend in Cd concentration, especially the cotton strip. Interestingly, our study found soil factors had the highest relative influence on decomposition. A higher soil microbial moisture use efficiency in the mid-latitude region during litter decomposition may be attributed to the adaptability of microorganisms. Our research demonstrated the consistency of lab test patterns with the field experiments, emphasizing the distinctions between standardized and conventional litter. This study not only revealed the influence mechanism of soil moisture and Cd on litter decomposition rate but also emphasized the important role of microorganisms in the litter decomposition process, which provided a new perspective for a deeper understanding of the ecosystem carbon cycle and heavy metal pollution.

Secondary Organic Aerosol Formation from the Photooxidation of Aromatic Ketone Intermediate Volatile Organic Compounds.

Oxygenated aromatics are substantial secondary organic aerosol (SOA) precursors, such as benzyl alcohol and phenolic compounds. Aromatic ketone intermediate volatile organic compounds (IVOCs), as a subclass of oxygenated aromatics, were found in anthropogenic source emissions and may contribute to SOA formation. However, the SOA yields and formation pathways of aromatic ketone IVOCs remain unknown. In this study, the photooxidations of aromatic ketone IVOCs in the absence and presence of NOx were studied in an oxidation flow reactor, and the particle- and gas-phase oxidation products were measured. The maximum SOA yields of benzophenone and 1,2-diphenylethanone are 0.24 and 0.33-0.35, respectively, relatively high among oxygenated aromatics. The SOA yields in the presence of NOx are 2-3 times higher than those in the absence of NOx in the late stage of oxidation. As the photooxidation proceeds, H/C of SOA slightly increases with O/C, and a greater amount of more-oxidized ring-retaining products exists in the particle phase in the presence of NOx. Based on gas-phase products and possible reaction pathways, functionalization of benzoic acid via the phenolic pathway is favored in the presence of NOx. Thus, our study highlights the significant SOA formation from aromatic ketone IVOCs, especially in the presence of NOx during long-time photooxidation.

Sequential Reactions of Acetylene with the Benzonitrile Radical Cation: New Insights into Structures and Rate Coefficients of the Covalent Ion Products.

Benzonitrile radical cations generated in ionizing environments such as solar nebulae and interstellar clouds can react with neutral molecules such as acetylene to form a variety of nitrogen-containing complex organics. Herein, we present results from mass-selected ion mobility experiments and coupled-cluster and DFT calculations for the sequential reactions of acetylene with the benzonitrile radical cation (C7NH5+•). The results reveal the formation of two covalently bonded adduct ions C9NH7+• and C11NH9+• with individual rate coefficients of 2.1(±0.4) × 10-11 cm3 s-1 and 1.1(±0.9) × 10-11 cm3 s-1, respectively measured at 334.5 K. The direct addition of acetylene onto the N atom of the benzonitrile cation results in the formation of a N-acetylene-benzonitrile+• radical cation with a calculated collision cross-section of 67.5 Å2 in perfect agreement with the measured cross-section of 67.5 Å2 of the C9NH7+• adduct. The measured collision cross-section of the second covalent adduct C11NH9+• (72.2 Å2) is also in excellent agreement with the calculated cross-section (71.2 Å2) of the lowest energy isomer of the C11NH9+• ion corresponding to the 2-phenylpyridine structure. The formation of the bicyclic 2-phenylpyridine radical cation is explained by the rapid conversion of the classical radical cation C11NH9+• into a distonic ion structure that can efficiently cyclize in an exothermic transformation to form the 2-phenylpyridine radical cation. This intriguing mechanism could explain the formation of N-containing complex organics in different regions of outer space. The current results are expected to have direct implications for the search for nitrogen-containing complex organics in space.

Anthropogenic Extremely Low Volatility Organics (ELVOCs) Govern the Growth of Molecular Clusters Over the Southern Great Plains During the Springtime

AbstractNew particle formation (NPF) often drives cloud condensation nuclei concentrations and the processes governing nucleation of molecular clusters vary substantially in different regions. The growth of these clusters from ∼2 to &gt;10 nm diameters is often driven by the availability of extremely low volatility organic vapors (ELVOCs). Although the pathways to ELVOC formation from the oxidation of biogenic terpenes are better understood, the mechanistic pathways for ELVOC formation from oxidation of anthropogenic organics are less well understood. We integrate measurements and detailed regional model simulations to understand the processes governing NPF and secondary organic aerosol formation at the Southern Great Plain (SGP) observatory in Oklahoma and compare these with a site within the Bankhead National Forest (BNF) in Alabama, southeast USA. During our two simulated NPF event days, nucleation rates are predicted to be at least an order of magnitude higher at SGP compared to BNF largely due to lower sulfuric acid (H2SO4) concentrations at BNF. Among the different nucleation mechanisms in WRF‐Chem, we find that the dimethylamine (DMA) + H2SO4 nucleation mechanism dominates at SGP. We find that anthropogenic ELVOCs are critical for explaining the growth of particles observed at SGP. Treating organic particles as semisolid, with strong diffusion limitations for organic vapor uptake in the particle phase, brings model predictions into closer agreement with observations. We also simulate two non‐NPF event days observed at the SGP site and show that low‐level clouds reduce photochemical activity with corresponding reductions in H2SO4 and anthropogenic ELVOC concentrations, thereby explaining the lack of NPF.

Genome-wide identification of a MADS-box transcription factor family and their expression during floral development in Coptis teeta wall

BackgroundMADS-box transcription factors have been shown to be involved in multiple developmental processes, including the regulation of floral organ formation and pollen maturation. However, the role of the MADS-box gene family in floral development of the alpine plant species Coptis teeta Wall, which is widely used in Traditional Chinese Medicine (TCM), is unknown.ResultsSixty-six MADS-box genes were identified in the C. teeta genome. These genes were shown to be unevenly distributed throughout the genome of C. teeta. The majority of which (49) were classified as type I MADS-box genes and were further subdivided into four groups (Mα, Mβ, Mγ and Mδ). The remainder were identified as belonging to the type II MADS-box gene category. It was observed that four pairs of segmental and tandem duplication had occurred in the C. teeta MADS-box gene family, and that the ratios of Ka/Ks were less than 1, suggesting that these genes may have experienced purifying selection during evolution. Gene expression profiling analysis revealed that 38 MADS-box genes displayed differential expression patterns between the M and F floral phenotypes. Sixteen of these MADS-box genes were further verified by RT-qPCR. The 3D structure of each subfamily gene was predicted, further indicating that MADS-box genes of the same type possess structural similarities to the known template.ConclusionsThese data provide new insights into the molecular mechanism of dichogamy and herkogamy formation in C. teeta and establish a solid foundation for future studies of the MADS-box genes family in this medicinal plant species.

Comprehensive analysis on Wnt signaling pathway to develop a novel signal modifier

Wnt signals play a key role in organ formation and function. Abnormalities in organ function or genetic diseases and carcinogenesis could point to issues with these signals, they are therefore an effective target for drug delivery. Dr Yuki Ikebuchi, Department of Pharmacy, The University of Tokyo Hospital, Japan, is heading up a team of researchers working to shed greater light on the Wnt signalling pathway. This will facilitate the development and delivery of more targeted drug therapies, helping patients. One element of Ikebuchi’s research is a detailed analysis on the Wnt signalling pathway to develop a novel signal modifier. As previous studies have found that Wnt molecules exert their physiological activities through glycosylation and lipid modification, a possible method to input signals downstream of the Wnt-Fzd complex is to crosslink and interact with Fzd molecules or co-receptors using antibody-like molecules. The researchers sought to obtain high-definition signal activation profiles of 10 types of Fzd molecules; something that hasnâ–™t been done before. At first, the team established the cell line, derived from mouse osteoblast-like MC3T3-E1 cells, in which endogenously expressed all Fzd and co-receptor genese were knocked out using CRISPR-Cas9 system. And then, they used adenoviruses containing the gene sequences of Wnt, Fzd and the co-receptor to transiently express them in knocked-out cells. The researchers will assess the resulting activation of downstream pathways by Luciferase assays using various reporter sequences. They will adopt a dual-glo assay that can correct the gene transfer efficiency and further enhance accuracy using NanoLuc.

On the use of isotopic differences of carbon fractions of biomass in plants to study transport flows and source-sink relations under different light conditions

It is shown that the differences in the isotopic composition of carbon in the water-soluble and water-insoluble fractions of plant leaf biomass, as well as phloem, are evolutionarily determined. They associated with metabolic reactions during assimilation and photorespiration and do not depend on the illumination mode and on the spectral ranges of headlights used in illumination. The above isotopic shifts are the cause of isotopic differences in assimilatory and photorespiratory carbon stocks that feed various metabolic processes. Due to the strict temporal and spatial organization of metabolism, carbon fluxes from the funds retain isotopic differences without complete mixing. The differences in the isotopic composition of carbon of the water-soluble fraction of biomass and carbon of phloem juice from carbon of the water-insoluble fraction are small (1–3%), but they are quite stable and easily fixed. The carbon of the water-soluble fraction is very close in isotopic composition to the carbon of the phloem and is noticeably enriched with the isotope 13C relative to the water-insoluble fraction, which makes it possible to use it as a marker in the study of assimilate transport in plants, especially during budding and fruiting. It is shown that the reason for the enrichment of autotrophic organs and tissues with isotope 12C relative to carbon of heterotrophic parts of the plant is the predominant participation in their formation of an isotopically light assimilation fund, whereas an isotopically heavy photorespiratory fund takes part in the formation of heterotrophic organs. It is shown that the manifestation of the formation of two isotopically different funds is the discovered relationship of the carbon isotope composition of leaves with their age.

Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy” Part VI

In this paper we provide the reader with a ready to use Group Contribution (GC) method for the heat of formation (gaseous state) of organics in the form of an Excel spreadsheet with all data, enabling further predictions, and an accompanying manual on how to use the GC model for predicting the heat of formation for organics. In addition, in order to widen the applicability of the method whilst retaining chemical accuracy compared to our previous publications on this topic, we include further chemical groups including acetals, benzyl ethers, bicyclic hydrocarbons, alkanediols and glycerol, polycyclic aromatic hydrocarbons, aromatic fluoro compounds, and finally several species which we include to illustrate how the GC model can be successfully applied to species we did not consider during the parameterization of the GC model parameters.

Enhanced organic aerosol formation induced by inorganic aerosol formed in laboratory photochemical experiments

Atmospheric inorganic gases such as NOx, SO2, and NH3 have diverse effects on the formation of secondary organic aerosol (SOA). A comprehensive investigation is necessary to fully understand the atmospheric processing of SOA. In this study, we examined the photooxidation of xylene isomers in the presence of inorganic gases using a combined facility comprising a smog chamber (SC) and an oxidation flow reactor (OFR). SC experiments at higher xylene concentrations and humid conditions revealed SOA yields of 37%, 39%, and 39% with NH3, compared to 15%, 11%, and 13% without NH3, for o-, m-, and p-xylene, respectively. This increase was primarily attributed to the enhanced formation of secondary inorganic aerosol (SIA) in the presence of NH3, consequently increasing aerosol surface area and aerosol water content (AWC). Vapor wall losses (VWL), estimated using a kinetic method, were substantial even with the elevated aerosol surface area provided by SIA. Additional photochemical reactions in the OFR showed a gradual increase in SOA mass and yield over an atmospheric equivalent aging time of 0.5–4.0 days. In the OFR, the SOA yield increased significantly when negligible xylene remained after SC reactions. Fresh SOA formation in the OFR might have decreased the oxygen-to-carbon ratio and oxidation state of carbon, which gradually increased with increasing OFR aging. High OH radical exposure in the OFR likely caused the photodegradation of SC-formed ON, as evidenced by an abrupt decrease in the NO+/NO2+ ratio measured. This study indicates that SOA formation potential of the aromatic hydrocarbon is highly underestimated without considering the combined effects of inorganic gases along with aging.

Rigidifying aggregation-induced emission luminogens by metal–organic framework formation for sensitive lateral flow immunoassay

T-2 toxin, the strongest toxic of type A trichothecenes, widely exists in barley, wheat, corn, oats, and even human food, which is urgent to establish a rapid and sensitive detection method for T-2 toxin. Herein, we developed a fluorescent lateral flow immunoassay (LFIA) for sensitive detection of T-2 toxin. Specially, the monoclonal antibody (mAb) was prepared by immunizing mice and cell fusion, and exhibited a low half maximal inhibitory concentration (IC50) of 0.482 ng mL−1. In addition, an aggregation-induced emission (AIE)-based metal-organic framework (HfMOFs) with excellent fluorescence performance (QY: 72.5 %) was developed as reporter. Benefiting from these advantages, the limit of detection (LoD) of HfMOFs-LFIA was 0.0487 ng mL−1, which was 7.7-fold lower than traditional nanoparticles-based LFIA (0.375 ng mL−1). In addition, HfMOFs-LFIA was used for the detection of T-2 toxin in actual samples and showed satisfactory recoveries (71.3 %–123.7 %) with coefficient of variation (2.96 %–14.07 %). Overall, the dual-improvement in mAb and label might power the development in LFIA, achieving innovative prospects for LFIA in food safety fields.

Mice with Lymphatic Dysfunction Develop Pathogenic Lung Tertiary Lymphoid Organs that Model an Autoimmune Emphysema Phenotype of COPD.

We have previously shown that mice with loss of C-type lectin-like type II (CLEC2), which have lymphatic dysfunction due to the role of CLEC2 in platelets for maintaining separation between the venous and lymphatic system, develop lung tertiary lymphoid organ (TLO) formation and lung injury that resembles an emphysema phenotype of chronic obstructive pulmonary disease (COPD). We now sought to investigate whether and how TLOs in these mice may play a pathogenic role in lung injury that is relevant to human disease. We found that inhibiting TLO formation using an anti-CD20 antibody in CLEC2-deficient mice partially blocked the development of emphysema. TLOs in CLEC2-deficient mice were rich in plasma cells and were a source of a broad array of autoantibodies. Chronic cigarette smoke exposure increased the size and number of lung TLOs in CLEC2-deficient mice, and was associated with increased markers of antigen presentation and maturation, leading to increased autoantibody deposition. Using lung tissue from COPD patients, we found an increase in lymphatic markers in patients with an emphysema phenotype and autoreactive TLOs compared to COPD patients without emphysema that lack prominent TLOs. Taken together, these results demonstrate that emphysema in mice with lymphatic dysfunction can be partially rescued by blocking TLO formation, and that these TLOs are source of autoantibodies that are exacerbated by cigarette smoke. Our work suggests that lymphatic dysfunction in mice may recapitulate some aspects an autoimmune emphysema phenotype that is seen in a subset of patients with COPD.

Self-Shielding Enhanced Organics Synthesis in an Early Reduced Earth's Atmosphere.

Earth is expected to have acquired a reduced proto-atmosphere enriched in H2 and CH4 through the accretion of building blocks that contain metallic Fe and/or the gravitational trapping of surrounding nebula gas. Such an early, wet, reduced atmosphere that covers a proto-ocean would then ultimately evolve toward oxidized chemical compositions through photochemical processes that involve reactions with H2O-derived oxidant radicals and the selective escape of hydrogen to space. During this time, atmospheric CH4 could be photochemically reprocessed to generate not only C-bearing oxides but also organics. However, the branching ratio between organic matter formation and oxidation remains unknown despite its significance on the abiotic chemical evolution of early Earth. Here, we show via numerical analyses that UV absorptions by gaseous hydrocarbons such as C2H2 and C3H4 significantly suppress H2O photolysis and subsequent CH4 oxidation during the photochemical evolution of a wet proto-atmosphere enriched in H2 and CH4. As a result, nearly half of the initial CH4 converted to heavier organics along with the deposition of prebiotically essential molecules such as HCN and H2CO on the surface of a primordial ocean for a geological timescale order of 10-100 Myr. Our results suggest that the accumulation of organics and prebiotically important molecules in the proto-ocean could produce a soup enriched in various organics, which might have eventually led to the emergence of living organisms.