ACS Earth and Space Chemistry最新文献

Metals are important components of atmospheric aerosols for both health and atmospheric reactivity. Coordination chemistry, leading to the formation of metal–ligand complexes, can alter metal solubility and their redox activity in solution; however, such processes have been so far predominantly studied via thermodynamic modeling approaches alone. Such approaches have indicated iron-oxalate complexes as major species of interest in urban environments. In this study, aerosol samples collected in the urban environment of Padua (Italy) are used to compare the speciation picture of iron obtained by thermodynamic modeling with that measured experimentally using X-ray absorption spectroscopy (XAS). The results showed broadly consistent speciation pictures between the two approaches, however, with some quantitative differences probably due to a discrepancy between bulk and single particle chemical composition of the aerosol samples. The XAS results showed the presence of iron-oxalate complexes in the samples, with both Fe(III) and Fe(II), and also suggested that most of the Fe may be mixed with organic matter on an atomic level. The thermodynamic modeling results indicated malonate as an additional important ligand besides oxalate and a potential candidate for explaining the mixed iron-organic nature of the aerosol samples.

Glycolamide [HOCH₂C(O)NH₂, GAm], the only isomer of glycine [H₂NCH₂C(O)OH] detected in the interstellar medium (ISM) to date, consists of an inherent peptide bond [C(O)NH] that is fundamental to protein synthesis and the origin of life. Despite its importance in ISM, detailed investigations on the reactivity of GAm under cosmic circumstances remain rather limited. In the present study, we performed the reaction involving H atoms and GAm in solid para-hydrogen (p-H₂) at 3.2 K and observed the exclusive formation of 2-amino-1-hydroxy-2-oxoethyl radical [HO^•CHC(O)NH₂] via H abstraction on the CH₂ moiety of GAm. We successfully characterized the infrared spectra of both Cis–cis (Cc)- and Trans–trans (Tt)-conformers of HO^•CHC(O)NH₂ from the reactions of H + Cc-GAm and H + Tt-GAm in a single experiment; the ratio of Cc:Tt conformers of GAm in the deposited matrix was estimated to be ∼3:2, and, after H abstraction, that of HO^•CHC(O)NH₂ remains approximately the same. In darkness, the increase in the infrared intensities of both conformers of HO^•CHC(O)NH₂ indicated that these radicals were formed from the reaction H + Cc-/Tt-GAm through tunneling, a possible route in dark interstellar clouds. This radical intermediate, HO^•CHC(O)NH₂, may serve as a potential precursor in the formation of higher-order amides bearing a chiral center, including lactamide and glyceramide (glycerol amide), after reactions with ^•CH₃ and ^•CH₂OH, respectively. In addition to the conventional condensation reaction in the process of polymerization for the formation of dipeptides such as malonamide in the dark regions of the ISM, the radical–radical reaction of HO^•CHC(O)NH₂ with NH₂^•CO might serve as an alternative pathway.

Criegee intermediates (CIs) are highly active molecules, which usually arise due to the ozonolysis of alkenes. They play an important role in many chemical reactions in both the lower and upper atmospheres of the Earth. Further dissociation products of CIs may interact with other atmospheric compounds to produce hydroxyl radicals, nitric and sulfuric acids, and other chemically active substances. In this work, we focus on one of the simplest and most easily formed Criegee intermediates, acetaldehyde oxide (CH₃CHOO), which exists in two possible forms: syn-CH₃CHOO and anti-CH₃CHOO, which differ in the orientation of the −OO group. Due to the high isomerization barrier between them, they are usually considered different isomers. In this work, we study the dissociation reactions of this molecule based on the assumption that the reaction can start from either syn-CH₃CHOO or anti-CH₃CHOO isomers. For that, we have determined the relative maximum and minimum energies as well as the main isomerization/dissociation reaction pathways based on the ab initio B3LYP/CCSD(T) calculations followed by the estimation of rate constants and product yields by the RRKM method. It was found that the main dissociation products in both cases are OH, CH₂CHO, and CH₃CO radicals, whereas the methyldioxirane decomposition products include methane, CO₂, and acetic acid. At high internal energy, a small number of O(¹D) atoms may be produced. The dissociation product yields of syn- and anti-isomers are generally quite different.

The cryovolcanic regions of Titan offer transient opportunities for prebiotic molecules to exist in water–ammonia solutions on the surface of the Saturnian moon. The upcoming NASA’s Dragonfly mission will search for high nitrogen concentrations and amino acids on Titan’s equatorial terrains. Cryovolcanic features, however, are most common on the polar regions. To mitigate the distance, bubble bursting may encapsulate the prebiotic molecules into aerosols, which Titan’s Hadley circulation would subsequently transport to the equator. We investigate whether alanine and glycine survive this meridional journey. Despite the unconstrained meridional wind velocities, our results suggest that the amino acids can survive the transport through the mesosphere. Dragonfly may find cryo-volcanogenic amino acids on Titan’s equator. Further, the interaction between the two amino acids increased 10-fold the photodegradation rate of glycine. We justify it based on changes in the environment polarity.

Typhoon Khanun’s passage over Okinawa Island in July and August 2023 offered a valuable opportunity to investigate its influence on atmospheric composition, particularly biogenic volatile organic compounds (BVOCs) and secondary organic aerosols (SOA). While typhoons are recognized for transporting ozone from remote regions, Okinawa’s unique geographic location resulted in elevated ozone levels after the typhoon’s departure. This phenomenon was driven by strong southwesterly to northwesterly winds that transported polluted air masses from eastern China. The typhoon also triggered significant increases in BVOC emissions, notably monoterpenes. These emissions, coupled with the highly oxidizing conditions in the post-typhoon air mass, led to substantial SOA formation. Both OH and NO₃ radicals played crucial roles in oxidizing BVOCs, with NO₃ becoming increasingly important at night. This study emphasizes the intricate connection among meteorological events, forest ecosystems, and atmospheric chemistry. Continuous monitoring is essential to fully understand the impact of such natural disturbances on air quality and climate.

We present infrared absorption coefficients, cross sections, and band strengths calculated from reflection–absorption infrared spectroscopy (RAIRS) data of molecular ices deposited on a highly oriented pyrolytic graphite (HOPG) surface at 28 K. We also describe an estimated conversion factor (encompassing considerations from the metal-surface selection rule and metal-surface enhancement factor for graphite) to explain how these parameters compare to those calculated using transmission infrared methods. Further, we discuss the limitations of this method and the assumptions which must be considered when evaluating absorption parameters from RAIRS data. The two species studied here (methyl acetate and methyl propanoate) were chosen to test these methods, as they are both astrochemically relevant and have previously been reported in the literature, providing a reliable benchmark.

We present infrared absorption coefficients, cross sections, and band strengths calculated from reflection-absorption infrared spectroscopy (RAIRS) data of molecular ices deposited on a highly oriented pyrolytic graphite (HOPG) surface at 28 K. We also describe an estimated conversion factor (encompassing considerations from the metal-surface selection rule and metal-surface enhancement factor for graphite) to explain how these parameters compare to those calculated using transmission infrared methods. Further, we discuss the limitations of this method and the assumptions which must be considered when evaluating absorption parameters from RAIRS data. The two species studied here (methyl acetate and methyl propanoate) were chosen to test these methods, as they are both astrochemically relevant and have previously been reported in the literature, providing a reliable benchmark.

We report on a newly developed method for compound-specific isotopic analysis (CSIA) of carbon (δ¹³C) and nitrogen (δ¹⁵N) in underivatized pyrimidine (cytosine, uracil, and thymine) and purine (adenine, guanine, hypoxanthine, and xanthine) nucleobases. The nucleobases are isolated by multistep purification using high-performance liquid chromatography (HPLC). HPLC separation and its wet chemical pretreatments were optimized to isolate these nucleobases without the need for chemical derivatization. Subsequently, the carbon and nitrogen isotopic compositions of these underivatized nucleobases were analyzed by nanoscale elemental analysis/isotope-ratio mass spectrometry (nano-EA/IRMS). The δ¹³C and δ¹⁵N measurements of isolated standard nucleobases indicated minimal isotopic fractionation during the two-step HPLC purification. This HPLC × nano-EA/IMS methodology was utilized to determine the isotopic composition of nucleobases in spinach (δ¹³C: −27.0 to −19.8‰, δ¹⁵N: +2.8 to +6.7‰) and coastal sediment (δ¹³C: −14.9 to −9.2 ‰, δ¹⁵N: +4.5 to +9.0‰) samples. The CSIA of nucleobases can provide insight into how living organisms modulate their biochemical pathways in response to environmental and metabolic variations.

Selenium could enter the environment through different anthropogenic sources, posing a potential health risk at higher concentrations. Although dopant atoms incorporated into the Fe(III) oxide lattice play a controlling role in the environmental speciation and fate of various contaminants, their role is poorly understood at the mechanistic level. The present study is an in situ investigation of the surface reactions of selenite oxyanion at the pristine/Mn-doped hematite (Mn-Ht)–water interface to delineate the role of the dopant in interfacial speciation and adsorption characteristics of the selenium oxyanion. Total and species-specific selenium ions present in the supernatant, estimated at the end of the equilibration of selenite ions with an aqueous suspension of the doped hematite, revealed the adsorption of selenite ions followed by their fast surface-induced oxidative transformation to selenate ions. This redox change of selenite ions was further characterized by using cyclic voltammetry and differential pulse voltammetry methods. Electrochemical evidence revealed an increased electron transfer (ET) rate constant (0.023–0.197 s^–1) with Mn doping. The proposed mechanism is related to the suppression of electron–hole pair recombination with Mn doping in the hematite lattice. Due to the dopants, acceptor levels trap the photoelectrons produced in the Mn-Ht lattice; simultaneously, the photoholes collect in the valence band to execute the oxidative transformation of selenite anions to their oxidized species. As selenate exhibits weaker interactions with hematite than selenite ions, it is released into the supernatant phase. Our findings highlight the critical role that a dopant may play in mobilizing contaminants that otherwise will be strongly held by the pristine solid.

Calcium sulfate minerals are found in multiple environments on Earth and Mars, with chloride (Cl) salts widely distributed on both planets. Low-temperature studies have explored geochemical processes, including the formation of transient liquid water and ion migration on Mars. Some Cl-salts (e.g., NaCl and CaCl₂) can dissolve gypsum (CaSO₄·2H₂O) in certain environments, making gypsum-Cl salt interactions significant. Additionally, gypsum's geochemical transformation at high temperatures reveals dehydration pathways crucial for understanding Mars' aqueous history and potential for life. This study examines gypsum dehydration through (i) thermal analyses and (ii) interactions with Cl-salts over a temperature range of -90 to 400 °C. We applied three spectroscopic techniques (Raman, visible/near-infrared, and mid-IR) plus X-ray diffraction (XRD) to analyze these samples under variable conditions. This study also provides a low-temperature spectral data set for gypsum and gypsum-Cl salt mixtures, beneficial for orbital analyses. Our findings reveal that experimental (i) heating rates, (ii) temperature ranges, (iii) relative masses of gypsum and Cl-salts, and (iv) dehydration environments (e.g., in situ and in vacuo) influence Ca-sulfate phase formation. Although we find different results in some cases, this study demonstrates that changing experimental conditions affects the detectability and transformation of gypsum. Further, these results indicate that the geochemical environmental conditions on Mars play a role in gypsum's geochemical transformation to dehydrated components. This study also provides structural and chemical data for Ca sulfate assemblages from vibrational spectroscopy and XRD, which extends our knowledge of gypsum and related materials under variable conditions, thus aiding orbital and surface planetary analyses that may help to advance our understanding of planetary geochemistry on Mars.