ACS Earth and Space Chemistry最新文献

Mineral analysis is one of the most vital missions in Mars exploration. Laser-induced breakdown spectroscopy (LIBS) is suitable for in situ analysis of minerals on Mars because of its ability to substantially remove dust and analyze most major elements. However, the longevity of active LIBS technology is susceptible to the Martian atmosphere and environmental temperature. Assuming that the LIBS laser had a malfunction, reflectance spectra of surface materials could be acquired in passive mode to analyze minerals and rocks, as is done on the ChemCam and SuperCam instruments on the Mars Science Laboratory and Mars 2020 rover missions, respectively. In addition, passive reflectance can provide constraints on the mineral structure and depositional environment of the rocks encountered by the rover. In this work, we present a passive reflectance spectra method based on the MarSCoDe ground simulator using the spectrometer module of the prototype system to test its ability to acquire visible reflectance spectra. The work presents the reflectance spectra of 24 National Reference Materials from which we computed the spectral parameters of minerals and rocks. Chemometrics based on particle swarm optimization-support vector classification (PSO-SVC) are used to accomplish the recognition of various materials. The results show that the passive spectral method could acquire targeted visible reflectance information and identify materials effectively.

Measurements of atmospheric organic particle composition at higher altitudes are scarce. The present study discusses concentrations and sources of PM and organic constituents based on winter-time observations at Mount Tai and aircraft measurements above the North China Plain (NCP). For PM_2.5 at the mountain site, concentrations up to 94 μg m^–3 were measured. Correlations with surrounding cities indicated that, despite an observed boundary layer height below the sampling altitude (1534 m asl), polluted air masses from the plain ascended to the mountaintop, possibly due to orographic effects. Organic constituents showed mean concentrations ranging from ∼1 ng m^–3 for terpene-derived acids and some branched or unsaturated dicarboxylic acids but could reach up to ∼100 ng m^–3 for oxalic acid. A cluster heatmap revealed correlational relationships between the compounds that originate from sources, including traffic, combustion of coal, waste, and biomass as well as secondary formation. Average concentrations of most short-chain organic acids taken in the general upwind direction of Mount Tai at mean flight altitudes of ∼4000 m averaged 10–25% of the mountain ones outside haze periods, suggesting that chemical formation during high-altitude transport could have occurred. One flight sample showed high concentrations of up to 180 ng m^–3 for oxalic acid, which is comparable to mountain haze periods, corroborating earlier observations of elevated pollution layers in the area even at such altitudes. CAPRAM multiphase modeling reproduced selected mountain concentrations of malonic and succinic acids reasonably well, while an initial underestimation of oxalic acid could be reduced by including salt formation and thereby enhanced phase partitioning. Overall, this study addresses observational gaps at high altitudes over the NCP and suggests processes and sources that might also be relevant in other regions.

The recent discovery of organic matter exposed in patches on the surface of the asteroid Ceres has sparked considerable interest in its prospect as an emerging astrobiological target. The dwarf planet’s surface is also characterized by a pervasive display of salt minerals, which are suggestive of briny fluids at depth and ongoing geological activity that resulted in their emplacement. While these salt-rich subsurface liquid reservoirs can present enticing conditions for prebiotic chemistry to emerge, the connection between dissolved organic materials and the associated salt minerals upon exposure to Ceres’ surface environment has not yet been established. Here, we explore this fundamental relationship by investigating the chemistry of putative organic-bearing brines relevant to Ceres (composed of sodium, ammonium, carbonate, and chloride ions) upon freezing using infrared (IR) reflectance and Raman spectroscopies, specifically focusing on two representative amino acids (glycine and aspartic acid) and an N-containing aliphatic compound (hexylamine). The results indicate that the presence of these organic species in the brines leads to the formation of CO₂ (isolated in the water ice matrix) when flash-freezing to liquid nitrogen temperatures. In particular, the two amino acids produce significantly more CO₂ compared to the hexylamine-brine mixture. Slow-freezing conditions, on the other hand, do not exhibit such a behavior. The bicarbonate anions in solution (rather than the amino acids themselves) are confirmed to be the source of CO₂ by isotopic substitution experiments. Raman measurements subsequently hint at a possible reaction pathway involving the formation of a carbamate intermediate. These results not only exemplify the potentially important role of organic-salt interactions in Ceres’ evolution, but also provide insights into the fate of organics and future detection strategies of organic deposits on ocean worlds.

The formation of secondary organic aerosol (SOA), even from a simple hydrocarbon, is a complex, heterogeneous, multigenerational process involving hundreds of radical intermediate isomers and reaction pathways. Here, we compared the SOA generated from the reaction of the OH radical with five precursor species that differed in the identity of their primary functional group: n-decane, cyclodecane, 2-decanol, 2-decylnitrate, and 2-decanone. We compared results from smog chamber experiments and an explicit oxidation/gas-particle partitioning model of first-generation oxidation chemistry (Framework for 0-Dimensional Atmospheric Modeling–Washington Aerosol Module, F0AM-WAM) under two NO_x regimes: lower NO_x where RO₂ + HO₂ dominates and higher NO_x where RO₂ + NO dominates. Our results show that while functional group identity impacted the vapor pressures of the precursor species, this alone was unable to explain trends in experimental yields. Functional groups also directed the site of initiation with the OH radical and the propagation and termination reactions that follow, with the most significant differences noted for 2-decanol. SOA production was greater in the lower NO_x experiments for n-decane, 2-decanol, 2-decylnitrate, and 2-decanone due to production of the low volatility hydroperoxides and oxidized hydroxycarbonyls. Cyclodecane, however, produced more aerosol in higher NO_x experiments, potentially due to the enhanced formation of low volatility acetals or dimers in the presence of greater concentrations of nitric acid. Finally, we predicted that as much as 67% of the first-generation products may undergo subsequent oxidation to later-generation species. While model results from first-generation chemistry alone are unable to predict experimentally observed yields and chemistry, this work provides a foundation for the incorporation of additional (e.g., later-generation or heterogeneous oxidation chemistry, condensed-phase reactions, etc.) processes.

Vanadium (V) is a redox-sensitive trace metal often used as a paleoredox proxy in ancient marine sediments. However, our understanding of the early diagenesis of V is limited to laboratory-based simulations and bulk geochemical measurements of natural sediments. Microscale measurements are essential to exploring V geochemistry in organic-rich coastal sediments, where redox zonation changes over small spatial scales. Here, we describe an innovative in situ two-dimensional (2D) imaging approach to study redox-driven changes of V-bearing iron oxyhydroxides (lepidocrocite and ferrihydrite) in intertidal mudflat sediments of an Australian lagoon lake (Coombabah Lake, Queensland). Vanadium-bearing iron oxyhydroxides were suspended in a polyurethane-based hydrogel matrix, loaded on laser-cut acrylic probes, and exposed to mudflat sediments for up to 6 weeks. Changes in V speciation and Fe mineralogy were examined using synchrotron-based X-ray fluorescence (XRF) microspectroscopy for high-resolution chemical imaging of elemental (V, S, Fe) distributions combined with micro-X-ray absorption near-edge structure (μXANES) spectroscopy at the V and Fe K-edges for speciation analysis. Linear combination fitting of μXANES data revealed that solid-phase V^V was reduced to V^IV in the ferruginous zone of sediments and to a mixture of mainly V^IV and some V^III (up to 10–20%) in the sulfidic zone, where the reduction correlated with the degree of sulfidation and conversion of the iron oxyhydroxides to FeS (up to 96%). The combination of gel-based mineral probes with synchrotron-based μXRF tools can unravel small-scale geochemical relationships and provide new insights into the early diagenesis of trace elements in marine sediments.

Understanding the complex interactions between atmospheric aerosols and water vapor in subsaturated regions of the atmosphere is crucial for modeling and predicting aerosol–cloud–radiation–climate interactions. However, the microphysical mechanisms of these interactions for ambient aerosols remain poorly understood. For this study, size-resolved samples were collected from a high-altitude, relatively clean site situated in the Western Ghats of India during the monsoon season, in order to study background and preindustrial processes as a baseline for climate functioning within the context of the most polluted region of the world. Measurements of humidity–dependent mass-based growth factors, hygroscopicity, deliquescence behavior, and aerosol liquid water content (ALWC) were made by a novel approach using a quartz crystal microbalance based on a piezo-electric sensor. The climate-relevant fine-mode aerosols (≤2.5 μm) exhibited strong size-dependent variations in their interactions with water vapor and contributed a high fraction of ALWC. Deliquescence occurred for relatively large aerosols (diameter >180 nm) but was absent for smaller aerosols. The deliquescence relative humidity for ambient aerosols was significantly lower than that of pure inorganic salts, suggesting a strong influence of organic species. Our study establishes an improved approach for accurately measuring aerosol water uptake characteristics of ambient aerosols in the subsaturated regime, aiding in the assessment of radiative forcing effects and improving climate models.

Ni and Co are critical elements for the world economy and modern technologies. Mafic and ultramafic deposits represent low-grade yet abundant alternatives to traditional Ni and Co ores. In this work, density functional theory (DFT) with the Hubbard U correction (DFT+U) was used to simulate the incorporation of Ni and Co in forsterite (Mg₂SiO₄), the Mg endmember of olivine, a common mineral in mafic and ultramafic rocks. Hubbard U terms for Ni and Co were parametrized using a series of oxide, hydroxide, carbonate, silicate, and sulfide minerals relevant to extraction and recovery of Ni and Co from mafic and ultramafic deposits. Electronic, energetic, magnetic, and structural properties were considered in the parametrization. For each of Ni and Co, an effective Hubbard correction (U_eff) value that optimized agreement with either experimental data or a hybrid exchange-correlation functional for all of the minerals considered is reported. DFT+U ab initio molecular dynamics (AIMD) simulations of Ni and Co incorporated into the M1 and M2 octahedral sites of forsterite were then performed. Ni and Co substitution in the M1 site was more energetically favorable than substitution in the M2 site, in agreement with published partition coefficients. AIMD trajectories were used to compute extended X-ray absorption fine structure (EXAFS) spectra of Ni in the M1 and M2 sites for direct fitting to a published experimental spectrum of Ni in a natural San Carlos olivine sample. The results of the fit indicated that ordering of Ni in the M1 site was not as strong at the low Ni concentrations relevant to mafic and ultramafic silicate minerals as that at the higher concentrations of the Ni-Mg olivine solid solutions studied to date.

With its large size, dense atmosphere, methane-based hydrological-like cycle, and diverse surface features, the Saturnian moon Titan is one of the most unique of the outer Solar System satellites. Study of the photochemically produced molecules in Titan’s atmosphere is critical in order to understand the mechanics of the atmosphere and, by extension, the interactions between atmosphere, surface, and subsurface water ocean. One example is propyne vapor, a photochemically produced species in Titan’s upper atmosphere expected to condense in Titan’s stratosphere at lower altitudes. Propyne may also be a trace species in Titan’s stratospheric co-condensed ice clouds detected by the Cassini Composite InfraRed Spectrometer. Bulk structural characterization of propyne ice is currently incomplete and is lacking in published laboratory Raman spectra and X-ray diffraction data. Here, we present a laboratory characterization of propyne ice, including the first published X-ray diffraction and Raman spectroscopy results for propyne ice.

The stable nitrogen isotope composition (δ¹⁵N) of atmospheric ammonia (NH₃) and ammonium (NH₄⁺) has emerged as a potent tool for improving our understanding of the atmospheric burden of reduced nitrogen. However, current chemical oxidation methodologies commonly utilized for characterizing δ¹⁵N values of NH₄⁺ samples have been found to lead to low precision for low concentration (i.e., < 5 μmol L^–1) samples and often suffer from matrix interferences. Here, we present an analytical methodology to extract and concentrate NH₄⁺ from samples through use of a sample pretreatment step using a solid phase extraction technique involving cation exchange resins. Laboratory control tests indicated that 0.4 g of cation exchange resin (Biorad AG-50W) and 10 mL of 4 M sodium chloride extraction solution enabled the complete capture and removal of NH₄⁺. Using this sample pretreatment methodology, we obtained accurate and precise δ¹⁵N values for NH₄⁺ reference materials and an in-house quality control sample at concentrations as low as 1.0 μM. Additionally, the sample pretreatment methodology was evaluated using atmospheric aerosol samples previously measured for δ¹⁵N-NH₄⁺ (from Changdao Island, China), which indicated an excellent δ¹⁵N-NH₄⁺ match between sample pretreatment and no treatment (y = (0.98 ± 0.05)x + (0.11 ± 0.6), R² = 0.99). Further, this methodology successfully extracted NH₄⁺ from aerosol samples and separated it from present matrix effects (samples collected from Oahu, Hawaii; pooled standard deviation δ¹⁵N-NH₄⁺ = ± 0.5‰,n = 16 paired samples) that without pretreatment originally failed to quantitatively oxidize to nitrite for subsequent δ¹⁵N isotope analysis. Thus, we recommend applying this sample pretreatment step for all environmental NH₄⁺ samples to ensure accurate and precise δ¹⁵N measurement.

Acetylene, among the multitude of organic molecules discovered in space, plays a distinct role in the genesis of organic matter. Characterized by its unique balance of stability and reactivity, acetylene is the simplest unsaturated organic molecule known to have a triple bond. In addition to its inherent chemical properties, acetylene is one of the most prevalent organic molecules found across the Universe, spanning from the icy surfaces of planets and satellites and the cold interstellar medium with low temperatures to hot circumstellar envelopes where temperatures surge to several thousand kelvins. These factors collectively position acetylene as a crucial building block in the molecular diversification of organic molecules and solids present in space. This review comprehensively discusses the formation and expansion of carbon skeletons involving acetylene, ranging from the formation of simple molecules to the origination of the first aromatic ring and ultimately to the formation of nanosized carbon particles. Mechanisms pertinent to both hot environments, such as circumstellar envelopes, and cold environments, including molecular clouds and planetary atmospheres, are explored. In addition, this review contemplates the role of acetylene in the synthesis of prebiotic molecules. A distinct focus is accorded to the recent advancements and future prospects of research into catalytic processes involving acetylene molecules, which is a significant instrument in driving the evolution of carbon complexity in the Universe. The insights garnered from this review underscore the significance of acetylene in astrochemistry and potentially contribute to our understanding of the chemical evolution of the Universe.