ACS Earth and Space Chemistry最新文献

Over the past three decades, the dynamic variations of nutrients in coastal-estuarine rivers have led to differential changes in nitrogen and phosphorus in the Bohai Sea, North China. Although land use changes have been demonstrated to have profound effects on nutrient accumulation in estuaries and marginal sea by numerous studies, few efforts have been based on decades of data set incorporating specific land use types spanning large geographic areas, limiting relevant knowledge. In this study, a comprehensive data set for nutrients in the coastal-estuarine water of the Bohai Rim Region (BRR), North China, was compiled to reveal the impacts of land use transitions on dynamic spatiotemporal variations of nitrogen and phosphorus. Results indicated that the expansion of construction land increased most nitrogen and phosphorus in estuarine waters in the BRR, especially in the Hai River (HR), Yellow River (YR), Liao River (LR), and Luan River (LNR). During the 1990s to 2010s, a 58% expansion in construction land led to a 95% rise in ammonium (NH₄⁺-N) in the Haihe River, resulting from the sewage and domestic pollution discharge from two megacities, Beijing and Tianjin. Meanwhile, in Xiaoqing River (XQR), a 200% expansion in agricultural land during the 1990s to 2000s corresponded to a 30% increase in estuarine dissolved inorganic nitrogen (DIN) concentrations, suggesting that the contribution of non-point source pollution to estuarine waters should be emphasized in this region. This study indicated that nutrient dynamics in the HR estuary was mostly driven by construction land changes, with nitrogen inputs from industry and domestic wastewater, while nitrate (NO₃^–-N) was primarily impacted by dam construction. The enrichment of nitrogen in XQR and phosphorus/nitrogen in YR was mainly due to agricultural growth and fertilizer application. However, the loss of grasslands had a greater impact on NO₃^–-N in the increased industrial land, and agricultural fertilizers affected the LR. What’s more, wetland restoration reduced the LR’s total phosphorus concentration post-2010. The studied estuaries had WQI levels that attained or were close to “bad” status during the last 30 years. However, the influence of policy, especially land use change, has substantially altered nutrient deposition in coastal rivers in the BRR. This study provided a more comprehensive understanding of the causes of temporal and spatial variability in nutrient dynamics and implemented watershed-coast management approaches to improve water quality and support ecological sustainability in the BRR.

The recent observation of complex organic molecules (COMs) in interstellar ices by the James Webb Space Telescope (JWST), along with previous gas-phase detections, underscores the importance of grain surface and ice mantle chemistry in the synthesis of COMs. In this study, we investigate the formation and carbon isotope fractionation of COMs by constructing a new astrochemical reaction network that distinguishes the position of ¹³C within species (e.g., H¹³COOCH₃ and HCOO¹³CH₃ are distinguished). We take into account the position of ¹³C in each species in gas and solid phase chemistry. This new model allows us to resolve isotopomer-specific ¹²C/¹³C ratios of COMs formed in the star-forming cores. We consider thermal diffusion-driven radical–radical reactions on the ice surface and nonthermal radiolysis chemistry in the bulk (surface + mantle) ice. We find that carbon isotope fractionation of the functional groups in COMs appears through both nonthermal radiolysis in cold environments and thermal diffusion in warm environments, depending on the COMs. In particular, COMs containing methyl groups show isotopomer differences in ¹²C/¹³C ratios that reflect their formation pathways and environments. These isotopomer-resolved fractionation patterns provide a diagnostic tool to probe the origins of COMs in star-forming cores. Our results suggest that future comparisons between high-sensitivity isotopic observations and isotopomer-specific models will be helpful for constraining the relative contributions of thermal and nonthermal formation processes of COMs.

Gaseous mercury (Hg(0)) supersaturation and evasion from surface seawater are commonly attributed to a combination of biotic and photochemical reduction of divalent mercury (Hg(II)). This aqueous reduction and subsequent Hg(0) loss constrain methylmercury production, thereby limiting its bioavailability to marine food webs. Despite the pivotal role of Hg(II) reduction in the global biogeochemical mercury cycle, the mechanism and relative importance of Hg(II) photoreduction in seawater remain poorly understood. To address this gap in knowledge, we conducted shipboard Hg stable isotope photoreduction experiments using natural seawater collected from the North Pacific Subtropical Gyre. Our results indicate that Hg(II) photoreduction in surface seawater is largely controlled by indirect photolysis of HgCl₂. This represents a mechanism that contrasts with freshwater systems, where direct photolysis of Hg(II) dominates. Furthermore, by comparing experimental results with the stable isotopic composition of Hg in seawater and marine particles, we conclude that dissolved Hg(II) photoreduction in seawater is largely ineffective at producing gaseous Hg(0). These findings point to microbial Hg(II) reduction as the likely driver of Hg(0) supersaturation and evasion in seawater. We recommend further investigations into this phenomenon, particularly the potential for Hg(II) photoreduction mediated by pico- and phytoplankton.

The structural response of a high-pressure phase of isobutyronitrile up to 6.12 GPa was studied by using high-pressure single-crystal X-ray diffraction, periodic density functional theory (DFT), and CrystalExplorer calculations. This phase is isostructural with a known low-temperature phase. Compression involves distortion of packing arrangements and shortening of hydrogen bonds. However, interaction energy calculations show stabilization from enhanced hydrogen bonds is offset by increasing steric repulsion. Steric contacts cause transient incompressibility between 1.88 and 2.17 GPa, overcome by higher pressure. Volume reduction, not hydrogen bonding, primarily drives compressibility. Significant steric repulsion develops by 5.21 GPa, preceding crystallinity degradation above 6.12 GPa.

Hematite is a widespread iron oxide on both Earth and Mars, and its detection on Mars has made it a key target in the search for past water activity and potential biosignatures. On Earth, hematite occurs in a range of geological settings. In this study, we investigate hematite from three contrasting terrestrial environments: Archean (>2.5 Ga) banded iron formations (BIFs), laterites from the Cretaceous–Paleogene (∼65 Ma) Deccan Traps, and Jurassic (∼145–201 Ma) sedimentary concretions from Kutch, Gujarat, India. A multitechnique approach combining petrography, X-ray diffraction (XRD), Visible and Near-Infrared (VNIR) spectroscopy, and X-ray Absorption Spectroscopy (XAS) reveals distinct mineralogical and structural features across these samples. XANES data confirm Fe³⁺ as the dominant oxidation state, although subtle edge shifts in certain samples suggest incomplete oxidation. EXAFS analysis reveals Fe–O distances near 1.95–2.00 Å and variable Fe–Fe interactions, indicating differences in crystallinity and structural order. In particular, the superior type BIF sample exhibits diminished Fe–Fe coordination and shortened Fe–O paths, suggestive of ferrihydrite-like precursors and potential microbial mediation. WT-EXAFS mapping further highlights structural differences, with BIF samples displaying stronger midrange order compared to more disordered hematites in laterite. VNIR spectra show diagnostic absorption features near 0.65 and 0.85 μm, with weaker signals in BIF (superior type) possibly reflecting biogenic or diagenetic influences. These results underscore the value of integrated mineralogical and spectroscopic methods in distinguishing hematite formation pathways and provide a terrestrial analog framework for interpreting Martian hematite deposits and assessing possible biosignatures.

This study aimed to estimate source contributions to ambient fine particulate matter (PM_2.5) and volatile organic compounds (VOCs) measured at Raipur, Central India, during the periods of October 2015–September 2016 and November 2021–June 2022. Chemical compositions (15 elements, nine water-soluble ions, organic carbon [OC], and elemental carbon [EC]) for 164 PM_2.5 filter samples and 120 absorbent samples (21 VOCs) were used as input to receptor models (USEPA UNMIX 6.0 and PMF 5.0 models) for source apportionment. The results revealed four PM_2.5 source types and average relative source contributions: (1) road traffic (29.7%), (2) industrial emission (25.4%), (3) biomass burning (24.0%), and (4) coal combustion (20.9%). Average VOC source attributions were (1) vehicle engine exhausts (37.7%), (2) biomass burning and coal combustion (20.3%), (3) industrial emission/solvent usage (34.1%), and (4) biogenic emissions (7.90%). Nineteen locally derived PM_2.5 chemical source profiles for road traffic, domestic heating, and industrial emissions were used with the EV-CMB 8.2 model for comparison with PMF results, yielding similar source contributions.

Enzymes are seen as the link between chemistry and life; they replaced the initial work performed by RNA as the first catalyst, leading to the appearance of ribozymes. It has been proposed that prebiotic peptide synthesis occurs via multiple mechanisms. One plausible mechanism is that it happened in the prebiotic soup but a catalyst must have been present; otherwise, life would not have been possible, as shown by in vitro experiments. Although we do not have all of the information about the enzymes involved in the metabolism of the first life forms, there are currently extremophile microorganisms that live in extreme conditions like those of early organisms, such as during the Precambrian era. These microorganisms possess thermostable enzymes such as DNA polymerase from the bacterium Thermus aquaticus. Therefore, understanding how the first life forms could have originated in high-temperature extreme environments is crucial. The present work aims to evaluate the role of Taq DNA polymerase in synthesizing inorganic compounds from silico-carbonates of calcium, barium, or strontium (known as biomorphs) at high temperatures. The morphology of the synthesized biomorphs was observed using scanning electron microscopy (SEM). The micrographs showed that the presence of Taq DNA polymerase promotes the formation of spheres, regardless of the alkaline earth element used. The chemical composition and crystalline phases were determined by Raman and infrared spectroscopy and synchrotron X-ray diffraction (XRD). The analyses revealed that the calcium, barium, or strontium biomorphs are composed of crystalline material deposited on the surface of silicate films, forming silico-carbonates, such as calcite or vaterite (calcium), BaCO₃ (witherite), or SrCO₃ (strontianite), respectively. Our results demonstrate that Taq DNA polymerase is incorporated into the biomorph structure, forming spherical structures containing both mineral and organic phases, indicating that biomineralization occurs. These findings allow us to propose plausible pathways that played an essential role in the origin of life on Earth, suggesting that the mineral-organic phases that made up the proto-cell could be synthesized de novo in aqueous conditions likely present in the Precambrian. Finally, our current description is speculative because what seems to be feasible by prebiotic chemistry ideology does not seem to be compatible with those hypotheses that are biology-based. The opposite also holds true, such that notions of biological origins appear to be inconsistent with what prebiotic chemistry can provide.

Secondary organic aerosols (SOAs) significantly impact air quality and climate, yet their formation mechanisms under complex multipollutant conditions remain insufficiently characterized. This study systematically investigated the synergistic effects of both NO_x and NH₃ on toluene-derived SOA formation through comprehensive photooxidation chamber experiments. Chemical composition analysis was conducted using a high-resolution Orbitrap mass spectrometer (HR-MS). The experimental results demonstrated that increasing NO_x concentrations from 30 to 90 ppb reduced toluene SOA yield from 10.1 to 9.5% primarily owing to the NO_x-induced fragmentation of oxidation products as evidenced by elevated proportions of low-molecular-weight components (m/z < 100) in the SOA. The presence of NH₃ enhanced the SOA yield, but the facilitative effect of NH₃ on the SOA yield gradually weakened as the NO_x concentration increased. HR-MS results revealed that NH₃ promoted the formation of high-molecular-weight species (m/z > 200) and nitrogen-containing organics (NOCs). The facilitating effect of NH₃ on NOC formation strongly correlated with the variation in SOA yield under different NO_x conditions, suggesting that NOC formation is a principal mechanism through which NH₃ promotes SOA formation. Moreover, four imidazole compounds (IMs) were identified in the presence of NH₃, indicating that atmospheric toluene could serve as a precursor for these IMs. The observed nonlinear interactions between NO_x and NH₃ in SOA formation provide critical mechanistic insights for developing multipollutant control strategies, emphasizing the necessity for coordinated emission regulation of reactive nitrogen species to mitigate SOA pollution.

Time-dependent unimolecular dissociation rates of the C₁₂H₈ isomers acenaphthylene (ACY) and biphenylene (BPY) cations were measured using a cryogenic electrostatic ion beam storage ring. The neutral, cyano-functionalized tracers of ACY, but not of BPY, have been identified in the interstellar molecular cloud TMC-1 by radioastronomy. For both polycyclic aromatic hydrocarbons (PAHs), dissociation is rapidly quenched by recurrent fluorescence (RF). Master equation simulations including RF rate coefficients based on ab initio molecular dynamics calculations reproduce the measured dissociation rates. Only marginal differences in the survival probabilities of ACY and BPY in TMC-1 are indicated by these results, with both cations being stable for vibrational energies up to about 7.6 eV, which is 3 eV above the dissociation threshold energy.

Recent work has shown that divalent cations can perturb the viscosity and phase state of oxygenated organic particles in unexpected ways, sometimes leading to the formation of gel states. Despite the prevalence of divalent cations and oxygenated organic molecules in atmospheric aerosol, particularly in marine environments, the influence of gel states on the reaction rates is not well established. In this work, we measure and compare the impact of viscosity and gel formation on the ozonolysis chemistry of aerosol particles containing the unsaturated, oxygenated organic species ascorbic acid (AA). AA serves as an excellent proxy compound for highly oxidized molecules in the atmosphere. We measured the hygroscopic growth, phase state, viscosity, and water diffusion rate in binary particles containing AA and water and in ternary particles with an additional co-solute of either ammonium sulfate or CaCl₂. These measurements reveal gel formation in particles mixed with CaCl₂, as particles become rigid but allow for relatively rapid diffusion rates of water, consistent with previous observations of gel behavior. We measured the rate of ozonolysis of these particles under a range of relative humidity (RH) conditions, showing a clear decrease in the rate with decreasing RH, consistent with the increase in viscosity and slowed diffusion. Notably, we measured the rate of ozonolysis of particles existing in a gel state, showing that following an initial period of decay, the rate of reaction arrests, indicating that the organic material in the solid state is protected from the reaction. This work shows that viscous particles and gel particles exhibit different reactivity toward heterogeneous oxidants, with significant implications for how we understand the chemical evolution of aerosol particles in the atmosphere.