ACS Earth and Space Chemistry最新文献

Ferric chloride (FeCl₃) in sulfuric acid cloud droplets has been proposed to explain the inhomogeneous near-ultraviolet (UV) absorption visible at the Venusian cloud tops. However, the absorption spectrum of FeCl₃ in concentrated sulfuric acid does not appear to have been measured previously; here we report measurements under appropriate conditions of temperature and H₂SO₄/H₂O solution strengths. The choice of solvent has a significant effect on the measured spectrum. The reaction of FeCl₃ in aqueous H₂SO₄ to form ferric sulfate (Fe₂(SO₄)₃) was shown to be suppressed by adding HCl to the solution (as would occur in the Venusian atmosphere). The FeCl₃ spectrum in sulfuric acid is shown to be in good agreement with observations of the unknown absorber in Venus’ atmosphere. The presence of Fe₂(SO₄)₃, which absorbs strongly below 320 nm, should be considered when reconstructing Venusian spectra to avoid misattribution of absorption in this spectral region to SO₂, potentially leading to an overestimation of the SO₂ cloud top concentrations.

The formose-type reaction is widely regarded as a key process in the formation of sugars including ribose, a component of RNA, which is essential for life. Aqueous alteration in meteorite parent bodies constitutes one of the potential extraterrestrial environments wherein formose-type reactions could have occurred. The reaction could have been driven by ionizing radiation from radionuclide decay and the decay heat. Furthermore, this heating process may have released metal ions from the meteorite minerals, further enhancing the reaction. While hydrothermal experiments have been conducted to simulate such environments, the role of radiation in this process has rarely been considered. However, we have shown that radiation plays a key role in studying the prebiotic synthesis of sugars during the early stages of aqueous alteration of meteorite parent bodies. To investigate the effects of catalysts under irradiation, meteorite parent body simulants were irradiated with γ-rays at room temperature, with ammonia, calcium hydroxide, glycolaldehyde, and olivine serving as catalysts, and the production of aldoses was examined. As a result, these catalysts enhance aldose production under γ-ray irradiation. However, the effects of calcium hydroxide and olivine were found to be limited, potentially attributable to their lower solubility at room temperature. In contrast, ammonia and glycolaldehyde showed more significant effects. This observation indicates that in the early stages of aqueous alteration of meteorite parent bodies, where radiation such as γ-rays is likely to be the predominant energy source, dissolved catalysts play a more important role compared to solid catalysts.

We present alternate chemical routes for the production of simple sugars on prebiotic Earth that do not involve the formose reaction, whose mechanism of initiation involving the self-condensation of two formaldehyde electrophiles remains unclear. We show that HCN is the only carbon-containing prebiotic molecule required for the production of short- and medium-chain aldoses and ketoses, wherein HCN serves as either a reactant or catalyst. In situ generation of H₂ from the decomposition of formic acid, produced from HCN hydrolysis, supports the two-electron reduction of cyanohydrins to imines, catalyzed by heavy or transition metals provided by asteroid or meteorite collisions with prebiotic Earth and subsequent imine hydrolysis to give aldehydic functionalities. Experimental evidence is provided to support some of the proposed pathways, including the control of glycolaldehyde self-condensation in the presence of cyanide ions to preferentially give C₅ aldononitriles (cyanohydrins) and cyclic imido-1,4-lactones, both precursors to aldopentoses. Molybdate-catalyzed aldose epimerization is discussed as a chemical progenitor to the transketolase reaction of the pentose phosphate pathway, whose mechanism of action may be more complex than presently understood.

Cryovolcanism is a phenomenon reported in dwarf planets and satellites in the solar system and is characterized by the eruptions of volatiles under low-temperature conditions. However, there are clearly limitations to understanding it fully from observations far from Earth. From this point of view, Antarctica is one of the most extreme environments on Earth and is a very important region for modeling the extraterrestrial environment. Here, we report a maximum soil CO₂ flux value of 6120 g m^–2 d^–1 and a total CO₂ output of 8355 t d^–1 from the hydrothermal environment (up to 57.6 °C) of Mt. Melbourne, an active volcano located in Antarctica. In addition, fumarolic gases have δ¹³C values of −13.9 to −4.2‰ with CO₂ concentrations of 21.2–36.2 vol %. The corrected helium isotope ratios (Rc/Ra) of the gases are up to 2.21, indicating the magma degassing of Mt. Melbourne. However, hydrogen and oxygen isotopes of the ice samples inside the ice caves and ice towers in the hydrothermal region, similar to their surroundings, suggest that they are of largely atmospheric origin. Nevertheless, the circulated water caused hydrothermal alteration, producing minerals such as kaolinite and gibbsite, which greatly affected the moss habitat and microbial distribution of small greenhouse systems. Thus, the observations in this Antarctic hydrothermal system could potentially provide clues about extraterrestrial biological activity through cryovolcanism.

Carbonyl sulfide (OCS) is currently the only securely detected sulfur-bearing species in interstellar ices, making it an ideal window into solid-state sulfur chemistry in dense star-forming regions. Previous astronomical observations of the OCS asymmetric stretching mode (ν₃) at ∼2040 cm^–1 (∼4.9 μm) demonstrate that interstellar OCS may be embedded in CH₃OH-rich ices, indicating that OCS likely forms in the coldest, densest parts of star-forming regions where catastrophic CO freezeout occurs. However, a significant portion of the OCS ice observations cannot be fit with binary OCS:CH₃OH laboratory ice mixtures alone, suggesting a greater degree of chemical complexity in the local ice environment. With this work, we aim to aid future studies of the abundance, physicochemical environment, and evolutionary history of interstellar OCS ice, now enabled for many more interstellar environments by the James Webb Space Telescope. We provide a library of new laboratory IR transmission spectra of the tetrahedron of the OCS in CH₃OH- and CO-rich ice mixtures, some of which also include H₂S and H₂O. Of these new spectra, the tertiary OCS:CO:CH₃OH ice mixtures provide the best fits to observations of high-mass protostars, providing further support for the hypothesis that the atom of the OCS forms with CH₃OH, possibly via chemical pathways involving frozen-out CO. We calculate apparent band strengths of the ν₃ mode in the OCS:CH₃OH and the OCS:CO:CH₃OH ice mixtures. The derived values are consistent (within uncertainties) with the apparent band strength of the feature in pure OCS ice, 1.2 × 10^–16 cm molec^–1. We therefore recommend using this value when quantifying interstellar OCS ice column densities.

Cycloalkanes, which represent a significant proportion of hydrocarbons released through fuel evaporation and exhaust, produce considerable amounts of secondary organic aerosol (SOA). However, cycloalkanes vary in the number of rings and alkyl branch lengths, leading to high complexity in SOA predictions. In this study, the Unified Partitioning Aerosol Phase Reaction (UNIPAR) model is extended to predict SOA formation via multiphase reactions of cyclohexane, decalin, and various branched cyclohexanes. UNIPAR employs a lumped product distribution, originating from an explicit gas mechanism, to process multiphase partitioning and in-particle chemistry for SOA formation. The product distributions of cyclohexane and decalin are created using explicit oxidation mechanisms. Product distributions of alkyl-branched cyclohexanes are created as a composite of those of cyclohexane and linear alkanes. UNIPAR is applied to predict SOA formation for cyclohexane, decalin, butylcyclohexane, and octylcyclohexane, under various NO_x levels and seed conditions, and compared to chamber data. Cyclohexane and decalin SOA formation occurs exclusively through particle-phase reactions due to ring-opening aldehydic products. When the NO_x level (HC ppbC/NO_x ppb) = 3 at given conditions, the oligomeric SOA fraction represents 99.8, 82.2, and 1.0% of mass formed from decalin, butylcyclohexane, and n-decane, respectively. Except cyclohexane, SOA yields of cyclic alkanes are insensitive to seed types. With increasing alkyl branch length, cycloalkanes have increased SOA yields, and their SOA formation behaves more similarly to linear alkanes. Due to insensitivity to seed and NO_x conditions, temperature is the key environmental parameter influencing the SOA yields of large cyclic alkanes.