ACS Earth and Space Chemistry最新文献

Hydrocarbons in organic sediments subducted into the interior of the Earth play a crucial role in the deep carbon cycle. In this study, the thermal reaction of pentacosane (n-C₂₅), a long-chain n-alkane, was experimentally investigated under high-pressure and high-temperature conditions relevant to a subducting slab. Gas chromatography–mass spectrometry (GC/MS) analyses of the reaction products revealed the formation of lighter n-alkanes, indicating that thermal cracking of n-C₂₅ occurred between 360 and 400 °C at 0.5 GPa in the presence of SiO₂. A comparison of the residual n-C₂₅ under dry and wet conditions suggested that the presence of water enhanced thermal cracking, even at 0.5 GPa. Heavier alkanes and amorphous carbon preferentially formed under dry conditions from addition and dehydrogenation reactions, respectively. By contrast, the IR spectra indicated the formation of oxygenated organic compounds containing –OH and –CO groups under wet conditions, implying that polymerization with oxidation preferentially progresses under wet conditions. These results suggest that the presence of water promotes the formation of diverse organic compounds in subducting slabs, including oxygen-bearing compounds, rather than amorphous carbon or graphite.

Lithium-ion battery technology is a key component of energy storage and the demand for lithium (Li) will continue to increase in the next decades. Dissolved Li in subsurface brines represents a growing segment of the overall Li resource, and accurate estimates of Li concentrations in geological formations is crucial for its efficient management. This study employs advanced machine learning models to predict Li concentration in the Gulf Coast Basin using a comprehensive geochemical data set developed by the USGS. Six machine learning models-Gradient Boosting, Random Forest, K-Nearest Neighbor, Support Vector Regression, Neural Networks, and Extreme Gradient Boosting-were implemented and their accuracy compared and contrasted. In order to improve prediction accuracy, we also introduced a Multi-Target Sequential Chaining approach that imputes missing data from the data set sequentially. We tested three different data scenarios: (1) using the original data set (with outliers), (2) using the data set with outliers removed, and (3) introducing altered outliers to analyze model sensitivity. Results indicate that outliers impact model performance, with altered outliers helping assess robustness. The results of this work suggest spatial extensions of already known Li-rich areas (e.g., Smackover Formation) and confirm the low Li potential of most of the Gulf Coast.

Formic acid (FA) and acetic acid (AA) are abundant atmospheric carboxylic acids that play important roles in wet deposition acidity and secondary organic aerosol (SOA) formation. Despite their significance, observations of FA and AA gas-particle partitioning differ substantially from thermodynamic predictions, contributing to uncertainties in SOA burden estimates. In this study, we systematically investigate the effects of sodium chloride (NaCl) and ammonium sulfate ((NH₄)₂SO₄) on the partitioning of FA and AA. Our results reveal a consistent salting-out effect for both compounds in NaCl solutions, with Setschenow constants of 0.031 ± 0.002 m^-1 for FA and 0.066 ± 0.007 m^-1for AA. In contrast, (NH₄)₂SO₄ was found to have minimal impact on FA and AA partitioning at concentrations up to 2.5 mol kg^–1. pH-dependent experiments show a modest effect of acidity on FA and AA partitioning in the range of pH 1.5–3.5, though pH is predicted to impart a strong effect at pH levels above 3.5. These findings demonstrate that both ionic strength and pH influence gas-aqueous partitioning of small organic acids; however, the magnitude of observed salting effects is insufficient to fully explain the discrepancy between measured and predicted gas-particle partitioning of FA and AA in the atmosphere.

This study investigates the effects of wind speed on physicochemical properties such as water uptake, phase state, and viscosity at varying relative humidity (RH) of individual nascent sea spray aerosols (SSAs). We examined SSA sized within 0.1−0.6 μm generated from a wind-wave channel at two wind speeds: 10 m/s representing a wind lull scenario over the ocean and 19 m/s corresponding to wind speeds encountered in stormy conditions. Atomic force microscopy (AFM) was utilized to study two predominant SSA morphologies: core−shell and rounded. AFM phase state measurements at 60% RH revealed that shells of core−shells at 19 m/s were largely liquid, while those at 10 m/s were mostly semisolid or liquid with similar proportions, where semisolid shells exhibited higher viscosities at lower wind speed. Rounded SSAs were predominantly liquid or semisolid at 60% RH, with similar semisolid viscosities for both wind speeds. Increased water uptake was observed for core−shells at 19 m/s, while rounded SSA had similar hygroscopicity between the two wind conditions. Collectively, we observed a variation in the physicochemical properties of SSA generated at two wind speeds, which can be attributed to the impact of elevated wind speed on disrupting the sea surface microlayer film structure and composition.

Clay minerals play a vital role in methylmercury (MeHg) retention via surface complexation, significantly affecting its bioavailability and mobility. However, the structural complexity of clay mineral interfaces, especially at the edge surface and interlayer, limits experimental methods in precisely elucidating MeHg adsorption mechanisms at the molecular level. The first-principles calculations based on density functional theory (DFT) were conducted to investigate the microstructural dependence and molecular adsorption mechanisms of MeHg onto kaolinite (Kln) and montmorillonite (Mnt). The preferred adsorption configurations, charge transfer, and bonding mechanisms were determined using adsorption energy, electron density difference, Bader charge, projected density of states, crystal orbital bond index, and Wannier functions analyses. The adsorption capacity of MeHg follows the order of Mnt interlayer > Mnt (010) surface > Mnt (001) surface > Kln (010) surface > Kln (001) surface. Mnt has a higher active site density than Kln, contributing to its higher MeHg adsorption potential. The most stable structure on the Mnt interlayer is a monodentate SiO–Hg complex, and a bidentate SiO(AlOH)–Hg complex was found to be the most stable configuration on the Kln (010) surface. The Hg atom in MeHg gains charge from the surface O atom of Mnt and Kln, forming Hg–O polar covalent bonds. The bonding arises from the overlap and hybridization of Hg-5d and O-2p orbitals, with Mnt bonding driven by Hg-5dz² orbital, and Kln bonding involving Hg-5dyz, Hg-5dz², and Hg-5dx²-y² orbitals. These findings provide deeper molecular-level insights into MeHg-mineral interactions, offering significant implications for MeHg risk assessment and environmental remediation strategies.

Volatile organic compounds (VOCs) play important roles throughout the atmosphere, many of which are altitude dependent. This highlights the need for easily deployable devices to sample VOCs across different atmospheric layers. To address this, we present the design and initial application of a Time Resolved Automated Volatile organIc compounds Sampling system (TRAVIS). VOCs are collected on sorbent tubes, which are subsequently analyzed by a thermal desorption gas chromatography mass spectrometry pipeline. TRAVIS leverages a piezoelectric pump with an integrated pressure sensor for precise (0.1% flow rate relative standard deviation) and accurate (−3 ± 2% error in VOC quantitation) measurements. Via deployment on a tethered balloon system over an agricultural area, TRAVIS is used to show consistent vertically resolved VOC concentrations in a well-mixed (i.e., turbulent) atmosphere (e.g., 5% relative standard deviation for isoprene) and vertically dependent concentrations for a stratified atmosphere (e.g., prior to boundary layer development). We also show VOC information from an intermittent plume via both targeted and untargeted analysis, highlighting future applications for spurious events in agriculture, air quality monitoring, and environmental impact. Overall, the development of TRAVIS represents a lightweight, accurate, sensitive, and precise VOC sampling module for the scientific community.

Singlet oxygen (¹O₂) plays a critical role in the oxidative aging of atmospheric organic aerosols, yet the pH-dependent production mechanisms and molecular drivers remain poorly constrained. This study investigates ¹O₂ generation from atmospherically relevant dicarboxylic acids (pyruvic acid, 2-ketobutyric acid) and phenolic compounds (guaiacol, catechol, o-cresol) photosensitized by 3,4-dimethoxybenzaldehyde (³DMB*) across a pH range (2.5–6.5) mimicking atmospheric waters. Using furfuryl alcohol as a selective probe, we quantify steady-state ¹O₂ concentrations ([¹O₂]_ss) and demonstrate that acidic conditions (pH 2.5) enhance ¹O₂ yields by up to 40% for dicarboxylic acids and an order of magnitude for methoxy-substituted phenols (guaiacol: 4.32 × 10^–11 M vs catechol/o-cresol). Structural analysis reveals that protonation stabilizes triplet-state intermediates, while electron-donating groups (e.g., −OCH₃) promote energy transfer to O₂. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) further elucidates pH-dependent product formation: acidic conditions favor oligomers and polycarboxylic acids (X_c > 2.7), whereas neutral pH shifts pathways toward fragmentation. These findings highlight aerosol acidity as a key control on ¹O₂-driven oxidation, with implications for secondary organic aerosol (SOA) formation and organic pollutant degradation in atmospheric waters.

The nature of the photoionization of fullerenes is of significant interest to molecular astrophysics and astrochemistry. The C₆₀⁺ cation has been identified as a carrier of five of the diffuse interstellar bands (DIBs), and recent correlations between C₇₀⁺ electronic bands and a few weak DIBs have been presented. In this work, we present a high-resolution electronic spectrum of C₇₀⁺ recorded with He-tagging messenger spectroscopy, as well as the first threshold photoelectron spectrum (TPES) of C₇₀. We comment on the He cage stability around C₇₀⁺ and how it differs from that around other fullerenes, and we suggest some tentative vibrational assignments to the electronic spectrum based on a Jahn–Teller type formalism, which is expected from the C₇₀⁺ system. We use a novel semiempirical method employing the high-resolution He-tagging spectrum and create band fits that we compare with the TPES to derive the adiabatic ionization energy of C₇₀ (7.429 eV ± 0.015 meV). This methodology comes with some significant limitations but allows us to tentatively derive the energies of other excited states of the C₇₀⁺ cation from the TPES.

The [n]phenylene family of molecules, derivatives of graphenylene or low density graphene, are shown in this work to provide intriguing correlation to interstellar infrared (IR) spectra, showcasing an additional avenue beyond polycyclic aromatic hydrocarbons (PAHs) for the role that carbonaceous molecules may play in astronomical iIR spectra. Quantum chemical, anharmonic, vibrational spectra are generated in this work using pbqff, an open source program that streamlines the process of calculating quartic force fields (QFFs). Spectral data for all molecules employ a reparameterization of the semiempirical method PM6, and smaller molecules also have spectral data computed via the more traditional B3LYP/N07D level of theory. Analysis of these theoretical spectra has revealed noteworthy spectral features for this family of molecules in the region between 1500 and 1300 cm^–1, an area typically assigned to PAH cations. Additionally, the computed phenylene family C–H stretches lie slightly higher in frequency than those of most PAHs, but this family still exhibits strong out-of-plane bending motions in the far-IR. While 20% of the universe’s carbon is hypothesized to be locked in PAHs, this additional family of polycyclic antiaromatic hydrocarbons could be used for comparison to future interstellar spectra, possibly augmenting the forms of interstellar carbon available for astrochemical exploration.