ACS Earth and Space Chemistry最新文献

Phenolic aldehydes as brown carbon (BrC) chromophores may contribute to the mass of aqueous secondary organic aerosol (aqSOA) due to their potential as atmospheric photosensitizers. However, there is still a lack of knowledge about their sensitizing ability and the impact of environmental factors. In this work, we studied the photosensitized behavior of a phenolic aldehyde, syringaldehyde (SyrAld), in aqueous solutions. Under illumination, the influences of environmental factors such as precursor concentration, solution pH, codissolved inorganic constituents (NaCl and Na₂SO₄), and organic matter (vanillyl alcohol, VAL, a methoxyphenol produced during biomass burning) were investigated. Our results show that increasing pH and salt concentration causes a strong red shift in the absorption peak of SyrAld, and chloride salts and sulfate salts exert different effects on the photochemical reactivity of SyrAld. Interestingly, the opposite effects of SyrAld on VAL oxidation were observed at different wavelengths of light. Under UV-B irradiation, SyrAld inhibited VAL degradation by the light shielding effect, while under UV-A irradiation, photosensitization of SyrAld promoted VAL degradation. The major photooxidation products were identified as hydroxylated products induced by reactive oxygen species (OH radicals) and dimerized products by direct oxidation of triplet excited state SyrAld (³SyrAld*) using UPLC-Q-TOF-MS. This work suggests that environmental factors play significant roles in determining the fate of phenolic aldehydes in atmospheric waters.

The interaction of free cationic silicon oxide clusters, Si_xO_y⁺ (x = 2–5, y ≥ x), with dilute water vapor, was investigated in a flow tube reactor. Product mass distributions indicate cluster size-dependent dissociative water adsorption. To probe the structure and vibrational spectra of the resulting Si_xO_yH₂⁺ (x = 2–4) clusters, we employed infrared multiple photon dissociation spectroscopy and density functional theory calculations. The planar rhombic cluster core of the disilicon oxides (x = 2) appears to be retained upon dissociative adsorption of one H₂O unit, whereas a significant structural transformation of the tri- and tetra-silicon oxides (x = 3 and 4) is induced, resulting in an increased coordination of the Si atoms and more 3D cluster structures. In an astronomical context, we discuss the potential relevance of Si_xO_yH_z⁺ clusters as seeds for dust nucleation and catalysts for carbon-based chemistry in diffuse or translucent interstellar clouds, where all the necessary conditions for producing these species are found. In the produced clusters, the frequency of the isolated silanol Si–OH stretching vibrational mode is considerably blue-shifted compared to that in hydroxylated bulk silica and small inorganic compounds. This mode has a characteristic frequency range between 1200 cm^–1 (8.3 μm) and 1090 cm^–1 (9.2 μm) and is associated with the anomalously small Si–OH bond lengths in these ionised species. In infrared observations such high frequency Si–O stretching modes are usually associated with a pure bulk silica component of silicate cosmic dust. The presence of Si_xO_yH₂⁺ clusters in low silica astrophysical environments could thus potentially be detected via their signature Si−O band using the James Webb space telescope.

Condensation processes such as wet–dry cycling are thought to have played significant roles in the emergence of proto-peptides. Here, we describe a simple and low-cost method, differential Fourier transform infrared (FTIR) spectroscopy, for qualitative analysis of peptide condensation products in model primordial reactions. We optimize differential FTIR for depsipeptides and apply this method to investigate their polymerization in the presence of extraterrestrial dust simulants.

AlO, AlOH, and Al(OH)₃ can be formed in the gas-phase starting from nothing more than simple aluminum hydrides (AlH and AlH₂) and water molecules. All three products are probable precursors to aluminum oxide clusters that may initiate the nucleation of dust grains in the interstellar medium. Chemically accurate CCSD(T)-F12b/cc-pVTZ-F12 computations provide exothermic energetic values for these pathways. For example, the fully submerged formation of AlO is exothermic by 51.3 kcal mol^–1, and this should also lead to favorable kinetics. To aid in the detection of the recurring intermediate cis/trans-HAlOH with instrumentation located on the James Webb Space Telescope, among other observatories, rotational and vibrational spectroscopic data are reported by utilizing a highly accurate quartic force field methodology. The ν₂ stretching frequency at 1807.9 cm^–1 exhibits an anharmonic intensity of 185 km mol^–1 and the antisymmetric bend (ν₄) at 534.2 cm^–1 exhibits an anharmonic intensity of 213 km mol^–1 for the cis and trans isomers, respectively. These are roughly three times the antisymmetric stretch intensity of water. The cis isomer has a smaller dipole moment of 0.83 D, while the trans isomer contains a moderate dipole moment of 1.49 D. These properties indicate that both of these isomers can be observed through vibrational and rotational spectroscopic techniques.

The coupling effect of damming and urbanization on nutrient dynamics renders the aquatic environment sensitive and vulnerable, posing a significant global concern. However, the role of damming as a source or sink of nutrients remains uncertain. In this study, river water samples were collected in the Three Gorges Reservoir (TGR), which is recognized as the world’s largest hydropower engineering. By integrating solute chemistry and flux budget modeling, the status, source, and transformation of riverine nutrients were revealed, and the interplay between water storage and human inputs on TGR nutrient dynamics was discussed. The concentrations of TDN and DSi were 100.2 ± 46.1 μmol/L and 115.7 ± 14.1 μmol/L, respectively. NO₃^––N (77.9 ± 64.1 μmol/L) was the main species of TDN, with NH₄⁺–N and dissolved organic nitrogen accounting for only 2.5 and 19.7%, respectively. DSi was attributed to silicate weathering, while riverine NO₃^––N exhibited a significant influence from anthropogenic inputs. About 71.7% of NH₄⁺–N was retained or converted to NO₃^––N by nitration along the river. Evidence from the significant correlation (p < 0.05) between NO₃^––N/NH₄⁺–N and d-excess suggests that the evaporation process accelerated by damming promotes nitrification. Through the anthropogenic net nitrogen input model, atmospheric nitrogen deposition was the primary factor affecting nitrogen flux in TGR river water, highlighting the critical impact of urbanization. The estimated contribution fluxes of stored nitrogen from 1997 to 2020 exhibited a limited contribution ratio and decrease yearly, supporting that water level rise from damming promotes the release of stored nitrogen. This study enhances the comprehension of the anthropogenic impacts on the nutrient biogeochemical cycle in damming rivers, providing enlightenment for environmental health management in large reservoirs.

Cyanide is a critical reagent in prebiotic chemistry to promote the synthesis of precursors to biomolecules. Due to its strong nucleophilic properties, cyanide is integral to fundamental prebiotic pathways such as Strecker synthesis of amino acids, Oro’s synthesis of adenine, and the synthesis of pentose-like sugars and plays a key role in many prebiotic chemical networks. In aqueous systems with free ferrous iron, cyanide is strongly complexed by ferrous iron, forming stable ferrocyanide ([Fe(CN)₆]^4–) complexes that limit aqueous HCN pools. Here, we show that dissolved carbon monoxide, another prebiotically relevant molecule often present in environments in contact with Earth’s early atmosphere, can drive ligand-exchange reactions with ferrocyanide. Utilizing alkaline and hyperalkaline fluid compositions to simulate waters that have reacted with mafic and ultramafic rocks on early Earth, and moderate temperatures, we demonstrate that carbon monoxide is able to replace one or more cyanide ligands in ferrocyanide, consequently producing free cyanide and ferrocyanocarbonyl complexes. We also demonstrate that this [CN^–] can further react with prebiotic reagents, such as polysulfide, producing thiocyanate. Thus, this CO–CN ligand-exchange mechanism with ferrocyanide provides a plausible source of free cyanide in early Earth conditions, without a temperature extreme, to drive prebiotic reaction networks.

Ultrafine aerosols (d < 100 nm) are the most abundant particles in the atmosphere with strong implications for climate and air quality. Their formation and evolution remain a subject of significant uncertainty. Recently, the implication of a fundamental and hitherto unconsidered characteristic of ultrafine aerosols has been highlighted: the Young–Laplace pressure. Here, the photochemical reaction of vanillin, a proxy for biomass burning compounds, under various high pressures was investigated. Using high-resolution mass spectrometry and UV–visible spectroscopy, we demonstrated that vanillin photodegradation was faster by ∼40% under high pressures typical of atmospheric nanoparticles. Chemical characterization shows that dimer formation, ring-opening, and cleavage processes were greatly favored (i.e., up to ∼250%) at high pressures. While the formation of light-absorbing compounds appears to be nonaffected, their decomposition through photooxidative processes was shown to be 50% faster at high pressures. This study establishes that the high pressure inside nanometric-sized aerosols has to be considered as a key property that can significantly impact photochemical processes involved in aerosol growth and aging.

Evaporite salts from saline lakes and playas play active roles in the atmospheric cycles and the climate system, especially in the context of changing climate. This study investigates the chemical, isotopic, and hygroscopic characteristics of surface salt samples from two saline lakes, i.e., Mang’ai and Dalangtan (MA and DLT), in the Qaidam Basin. Samples from both lakes shared similar ionic compositions, with brines rich in Cl^–, Mg²⁺, and Na⁺, and lakebed salts being primarily NaCl-based. Disparities in the composition between MA and DLT crust salts were observed. Isotopic analyses revealed consistent δ³⁴S values within samples from a single site, hinting at a common origin. The sulfur source for the MA saline lake likely arises from nearby freshwater inflows and atmospheric deposits. The δ³⁷Cl values varied by sample type, with solid samples typically exhibiting higher values than brines, attributed to ³⁷Cl depletion during precipitation. Ionic composition largely determines hygroscopic properties. While brines started moisture absorption around 40% relative humidity (RH), lakebed salts commenced at 70% RH. The DLT playa salt, enriched in Na₂SO₄, demonstrated a unique behavior, responding significantly only above 80% RH. The layered DLT samples showcased variable hygroscopic behaviors, particularly the early moisture uptake of the topmost layer, despite its ionic similarity to another layer, hinting at molecular or hydration disparities. In conclusion, this investigation unravels the multifaceted relationship between salt evaporites composition and their implications for atmospheric chemistry.

Global efforts to build a net-zero economy and the irreplaceable roles of rare-earth elements (REEs) in low-carbon technologies urge the understanding of REE occurrence in natural deposits, discovery of alternative REE resources, and development of green extraction technologies. Advancement in these directions requires comprehensive knowledge on geochemical behaviors of REEs in the presence of naturally prevalent organic ligands, yet much remains unknown about organic ligand-mediated REE mobilization/fractionation and related mechanisms. Herein, we investigated REE mobilization from representative host minerals induced by three representative organic ligands: oxalate, citrate, and the siderophore desferrioxamine B (DFOB). Reaction pH conditions were selected to isolate the ligand-complexation effect versus proton dissolution. The presence of these organic ligands displayed varied impacts, with REE dissolution remarkably enhanced by citrate, mildly promoted by DFOB, and showing divergent effects in the presence of oxalate, depending on the mineral type and reaction pH. Thermodynamic modeling indicates the dominant presence of REE–ligand complexes under studied conditions and suggests ligand-promoted REE dissolution to be the dominant mechanism, consistent with experimental data. In addition, REE dissolution mediated by these ligands exhibited a distinct fractionation toward heavy REE (HREE) enrichment in the solution phase, which can be mainly attributed to the formation of thermodynamically predicted more stable HREE–ligand complexes. The combined thermodynamic modeling and experimental approach provides a framework for the systematic investigation of REE mobilization, distribution, and fractionation in the presence of organic ligands in natural systems and for the design of green extraction technologies.