ACS Earth and Space Chemistry最新文献

Red-bed mudstone is a typical soft rock with significant swelling characteristics, which often leads to expansion deformation when used in (ultra)high-speed railway subgrades. Given the widespread presence of soluble salts in natural environments, it is essential to investigate the influence of external ions on the rock expansion behavior. In this study, a multiscale approach integrating macroscopic expansion tests, microstructural evolution analysis, and molecular dynamics simulations was employed to elucidate the mechanism by which salt solutions inhibit mudstone expansion. The results demonstrate that salt solutions significantly suppress mudstone expansion within low concentration ranges, with a reduced expansion potential correlated to increased concentration or decreased cation valence. The critical concentrations for the equilibrium state of mudstone expansion in NaCl and CaCl₂ solutions are 1.20 and 1.00 mol/L, respectively. Positive correlation between the concentration of Na₂SO₄ solution and the expansion rate can be well predicted using a logistic model. Mudstone expansion induced by Na₂SO₄ includes three stages: a rapid expansion stage, a slow expansion stage, and an expansion growth stage. Three stages correspond to gypsum expansion, saltpeter expansion, and the crack-penetration crystal-expansion cycle. The ability of monovalent cations to neutralize the negative charge on the surface of clay minerals is weak, and the thicker double layer formed implies a wider diffusion layer and a larger water film thickness, while divalent cations significantly compress the thickness of the double layer. Molecular dynamics simulation reveals the nanoscale mechanisms of influence of monovalent and divalent ions on water–rock reactions, where cations reduce the diffusion rate of water molecules and weaken the interaction energy at the water–rock interface. Diffusion coefficient under the influence of Ca²⁺ is 0.62 × 10^–6 cm²/s and 0.17 × 10^–6 cm²/s, lower than that under the influence of Na⁺, indicating that divalent cations have a more significant inhibitory effect on the diffusion behavior of water molecules than monovalent cations. This multiscale study provides theoretical insights into the deformation mechanisms of red-bed mudstone in salt-rich environments, offering valuable guidance for the design and maintenance of (ultra)high-speed railway subgrades.

To demonstrate the potential for bismuth(III) (Bi)-based materials to sequester subsurface contaminants in situ, aqueous batch experiments were performed to determine how sediments impact the sequestration of technetium (Tc), uranium (U), chromium (Cr), and iodine(I) with bismuth subnitrate (BSN) and bismuth oxyhydroxide (BOH). Results of these experiments demonstrated that Bi-based materials have the potential to rapidly remove colocated contaminants over a range of geochemical conditions representative of the Hanford Site and in the presence of Hanford subsurface sediments. In aqueous batch experiments without sediment, the hydrolysis of both BSN and BOH resulted in a lowering of the pH (to as low as 2.4 with BSN or 5.9 with BOH). In the presence of sediment, the pH was buffered at ∼7–8 for both systems (BOH and BSN). In the absence of sediment, BOH readily sequestered U(VI) from its 2.3 mg/L solution under challenging conditions of a high solution-to-solid material ratio of 1000 mL/g or even when the U(VI) concentration was increased to 150 mg/L at a solution-to-solid material ratio of 200 mL/g. Cr(VI) was likewise readily removed from the aqueous phase at a concentration of 0.05 mg/L. A greater quantity of BOH (i.e., at a solution-to-solid ratio of 100–200 mL/g) was required for complete removal of Tc(VII) and I(V); changes in solution chemistry suggest that this is due to competing reactions with other ions, including chloride (Cl^–) and sulfate (SO₄^2–). In the presence of sediment, removal of Tc(VII) and I(V) decreased by respectively 91% and 21% for BOH and 33% and 93% for BSN. The presence of sediment increased removal of U(VI) by BSN to nearly 100%, while only 17% of U was removed in the absence of sediment. This study demonstrates that Bi-based materials show promise as a remediation tool to remove multiple contaminants from contaminated sediments, with the removal efficiency dependent on the amount of Bi-based material present in the sediment.

The Chang’e-6 (CE-6) mission returned the first-ever farside lunar samples. The bulk chemical compositions of these samples could resolve key questions about lunar evolution and the nearside-farside dichotomy. However, obtaining accurate results from small sample aliquots (1–2 mg) remains a significant challenge for existing analytical techniques. Here we established an improved method for determining 50 (10 major and 40 trace) elements using only 1–2 mg samples by combining bomb digestion and inductively coupled plasma mass spectrometry for extra-terrestrial samples. This method significantly improves upon previous approaches by (1) eliminating sample loss during the weighing step and (2) accelerating complete sample dissolution by 6-fold (8 h vs 48 h). This method achieved the first comprehensive elemental analysis of the CE-6 lunar sample, including 10 previously undetected elements (Cu, Li, Zn, Be, Pb, W, Mo, Cs, Cd, and Sn). Our analysis revealed a low-Ti/low-Al/low-K signature of the CE-6 basalt sample, akin to the CE-5 basalts. The basalt exhibits depleted Ni, in contrast with the Ni-rich CE-6 soil, suggesting exotic meteoritic contamination in the bulk soil. The rare earth element pattern of the CE-6 basalt resembles that of nearside mare basalts, with concentrations falling within their range. Beyond lunar samples, this measurement procedure adapted to small sample sizes offers significant potential for studying future extra-terrestrial samples, including those from asteroids and Mars.

Urban ozone (O₃) levels have shown positive or stable trends despite reductions in nonmethane hydrocarbons (NMHCs) and O₃ precursors. As tailpipe NMHC emissions have significantly decreased in Japan, nontailpipe NMHC emissions are expected to play an increasingly important role in recent times. This has challenged the understanding of recently speciated NMHCs, suggesting potential sources of nontailpipe NMHC emissions. This study utilized 3-h average canister sampling to capture representative speciated morning C₄–C₁₁ NMHCs in a midsized city on weekdays and weekends (Sundays). We observed that light alkanes (C₄ and C₅), heavy alkanes (C₉, C₁₀, and C₁₁), and aromatics were not reduced even on Sundays compared with weekdays in summer. We identified that light alkanes and aromatics potentially originate from vehicular gasoline tank canister breakthroughs and/or refueling, permeation, and evaporative emissions. Moreover, heavy alkanes can potentially evaporate from petroleum-based organic solvents used in laundry facilities. The similar total NMHC levels observed on weekdays and Sundays in midsize cities during summer imply that tailpipe NMHC emissions are no longer major contributors. Therefore, evaporative or temperature-dependent emissions are expected to be vital in the future, particularly in warming climates.

Bismuth (Bi) materials are advantageous for the subsurface remediation of contaminants due to its low toxicity and cost. Depending on the groundwater pH and ions present, bismuth materials undergo structural transformations, enabling interactions with aqueous contaminants at legacy nuclear sites. Here, the performance of bismuth oxyhydroxide (BOH) and bismuth subnitrate (BSN) was investigated with respect to the uptake of iodine-129 (iodate (IO₃^–) or iodide (I^–)), chromium (chromate (CrO₄^2–)), uranium-238 (uranyl carbonate complexes, (UO₂(CO₃)_x ^2–2x) like UO₂(CO₃)₃^4–), and technetium-99 (pertechnetate, (TcO₄^–)) in arid and semiarid regions (e.g., western United States), specifically conditions representative of the geochemistry in the Central Plateau (200 Area) of the U.S. Department of Energy Hanford Site. The influence of solution chemistry on the time-dependent structural transformation of Bi-based materials between crystalline clusters and layered arrangements was assessed in experiments for up to 150 days using synthetic Hanford water. Aqueous environments, especially carbonate (CO₃^2–), increase rates of Bi-based material structural transformation. Depending on solution pH and [CO₃^2–], BOH, initially a disordered δ-Bi₂O₃-like phase (dis-BiO_w(OH)_x(NO₃)_y(CO₃)_z), transforms to a layered bismutite (lay-Bi₂O₂(CO₃)) with high affinities for IO₃^–, CrO₄^2–, and (UO₂(CO₃)_x^2–2x) complexes. The hydrolysis of BSN causes the pH to decrease from 7.98 to 3.38 such that an “unknown” phase with the general formula unk-Bi(NO₃)_x(OH)_yO_z, charge-balanced by nitrate (NO₃^–) is formed and has a high affinity for TcO₄^–. Overall, increasing concentrations of common groundwater anions result in smaller sized mineralogical transformation products with higher surface areas for contaminant sorption. The results corroborate that Bi-based materials are promising candidates for groundwater remediation at the Hanford Site.

The COVID-19 pandemic-driven lockdowns offer a unique opportunity to examine how reductions in anthropogenic emissions impacted atmospheric aerosol composition in urban environments. This study investigates the day-night variability of size-resolved water-soluble ions in ambient particulate matter (PM) collected in Metro Manila before (November 2019–February 2020) and after (November 2020–February 2021) lockdown implementation. Using tandem Micro-Orifice Uniform Deposit Impactors (MOUDIs), aerosol samples were collected during daytime (06:00–18:00) and nighttime (18:00–06:00) periods and analyzed for key ionic species (sulfate, ammonium, nitrate, oxalate, sodium, chloride, calcium, and magnesium) via ion chromatography. Submicrometer water-soluble mass declined post-lockdown, particularly during daytime, reflecting suppressed secondary formation under reduced anthropogenic activity, with substantial reductions in sulfate and ammonium. In contrast, concentrations in the supermicrometer range increased due to naturally higher sea salt levels. Chemical ratios reveal notable features post-lockdown and during daytime due to especially reduced sulfate levels: reduced chloride depletion (on percent basis), higher ammonium-to-sulfate ratios pointing to more excess ammonia available for reactions beyond neutralizing sulfate, and support for aqueous-phase processing preferentially forming more oxalate relative to sulfate. These findings underscore how both photochemistry and changes in anthropogenic activity influence aerosol composition, with implications for air quality and atmospheric processing in coastal urban cities.

The mineral composition, content, and organic matter enrichment in shale are significantly influenced by the sedimentary environment. However, there is limited understanding of how the sedimentary environment impacts the resistivity and polarizability of shale. This study conducts experimental tests on shale from the Longmaxi Formation (LMXF), employing techniques such as complex resistivity, X-ray diffraction, organic geochemistry, porosity, elemental geochemistry, and argon-ion polishing scanning electron microscopy. The results show that the lower part of the LMXF was deposited in an anoxic environment with high paleoproductivity and low detrital influx, where siliceous shale is developed. This part is characterized by high TOC content, enrichment of biogenic quartz and pyrite, well-developed OM pores, low resistivity, and high polarizability. In contrast, the middle-upper part of the LMXF was deposited in an oxic-dysoxic environment with low paleoproductivity and high detrital influx, which is featured by low TOC content, high clay mineral content, high resistivity, and low polarizability. Redox conditions and paleoproductivity primarily influence the TOC content and the formation of biogenic quartz. The content of pyrite is influenced by redox environments, while clay minerals and terrigenous quartz content are affected by paleoclimate and terrigenous input. The interconnected network of organic matter pores, along with other types of pores, and the content of pyrite are the primary reasons for the high TOC and low resistivity observed in LMXF shale. The pyrite content also influences the polarization effect of shale. Redox conditions and paleoproductivity positively influence conductivity and polarization, whereas terrigenous input and paleoclimate have inhibitory effects on both.

The isotopic composition of ocean water is crucial in studying water masses and mixing in deep oceans, isotope mass balance in ocean water regulated by high-temperature and low-temperature hydrothermal alterations, and the exchange of water among crust-ocean-mantle reservoirs. We collected 40 water samples from Challenger Deep and the water column above at the Mariana Trench (down to 10,923 m) and 12 from the Yap Trench (down to 6,300 m) in the western Pacific Ocean in three hadal cruises from 2016 to 2018. The δ²H values at the Mariana and Yap Trenches average 0.1 ± 0.2 ‰ (1σ error). The δ²H records from this study, together with existing databases, manifest that deep waters have δ²H values varying between −2 and +2 ‰ (except for the Weddell Sea, the Greenland, Iceland, and Norwegian Seas, and the Mediterranean Sea), with increasing values from the Southern Ocean to the Pacific and Indian Oceans, and to the Atlantic Ocean. The average δ¹⁸O value of water samples from both trenches is –0.04 ± 0.03 ‰ (1σ error). The correlation between δ¹⁸O and salinity distinguishes abyssal water masses at the study region, UCDW (Upper Circumpolar Deep Water) and LCDW (Lower Circumpolar Deep Water). These water samples from the Mariana and Yap Trenches gave an average ¹⁷O_excess value of −6 ± 1 ppm (1σ error). Our 52 data records of ¹⁷O_excess expand the 38 existing records for the deep ocean. Both δ²H and ¹⁷O_excess of modern ocean have rolled as anchor points to reconstruct compositions of Earth’s early ocean.

Wildfires impact air quality, climate, and health near and far from the emission source. Here, real-time size and chemical composition of 2,419,048 individual particles were measured with an aerosol time-of-flight mass spectrometer (ATOFMS) in Ann Arbor, MI, between September 8 and 18, 2018. Of these mainly submicron particles, 97%, by number, were identified as aged biomass burning (smoke) particles, characterized by potassium, organic carbon, and elemental carbon. These aged biomass burning particles also contained secondary ammonium, nitrate, sulfate, nitric acid, sulfuric acid, and organic aerosol, including dicarboxylic acids, amines, and organosulfates. The Navy Aerosol Analysis and Prediction System (NAAPS) global aerosol model tracked smoke from wildfires in western North America in an air mass traveling northeast that then mixed with anthropogenic and biogenic aerosol from southern Canada and northern U.S. before reaching southeastern Michigan. Together, the observational and model results indicate that smoke particles accumulated secondary aerosol, including from biogenic and anthropogenic sources, during long-range transport. While the measurements and model show similar concentrations of submicron aerosol mass present, the ATOFMS measurements show that the smoke and secondary aerosol were mixed within the same, rather than separate, individual particles. In fact, most models that evaluate aerosol impacts on air quality and climate treat smoke and secondary aerosol as separate externally mixed species, which has implications for cloud formation, optical properties, reactivity, and possibly health impacts. This study highlights the participation of wildfire smoke in secondary aerosol formation, with biomass burning aerosols serving as substrates for heterogeneous reactions, condensation seeds for gas-particle partitioning, and cloud nuclei for subsequent aqueous-phase reactions during long-range transport of primary wildfire emissions.

Microplastics (MPs) and nanoplastics (NPs) are widespread pollutants present across all environmental matrices, including the atmosphere. They originate anthropogenically from primary sources, like microbeads, glitters, industrial abrasives, etc., and from secondary sources through degradation of larger plastic products, textile fibers, tire wear, waste incineration, etc. Degradation processes, such as mechanical, photochemical, chemical, and microbial degradation, break down plastics into smaller particles and gaseous byproducts. Atmospheric degradation processes of MPs/NPs enhance their area/volume ratio and introduce oxygenated functional groups at the surface, which increases their hydrophilicity and interactions with other pollutants in the surroundings. Thus, MPs/NPs also act as great vectors for toxic substances, including heavy metals, polycyclic aromatic hydrocarbons, and persistent organic pollutants, amplifying their environmental and health risks. MPs/NPs have been detected in various human tissues and fluids. Being bio-inert, they cannot be metabolized and leave the body only through excretory routes. They not only interact with the human organs directly but also indirectly via releasing additives and adsorbed/absorbed pollutants and, thus, can exhibit higher toxicity compared to other atmospheric aerosols. Furthermore, atmospheric MPs/NPs influence radiative forcing and cloud formation, and their photodegradation also releases greenhouse gases, like CO₂, CH₄, and volatile organic compounds (precursors of ozone), linking plastic pollution to climate change. Despite their growing recognition, the study of atmospheric MPs and NPs remains in its infancy, with numerous uncertainties surrounding their behavior, fate, and effects. This review aims to highlight underexplored degradation pathways of atmospheric MPs/NPs that may be enhancing their environmental, health, and climatic implications. It also proposes the future directions for atmospheric MP/NP research.