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  • A Model for the Spectral Dependence of Aerosol Sunlight Absorption
    ACS Earth Space Chem. Pub Date : 2017-09-21
    August Andersson

    Sunlight-absorbing aerosols, e.g., black and brown carbon (BC and BrC), have a potentially large, but highly uncertain contribution to climate warming. The spectral dependence of the aerosol absorption in the visible and near-UV regime is almost universally well-described with a heuristic power law, where the exponent is termed the Absorption Ångström Exponent. However, the underlying physico-chemical causes for this relation are unknown. Here, a model is presented that predicts the emergence of the power law spectral dependence and unifies the absorption behavior of BC and BrC. Building on the theory of light-absorption in amorphous materials, the interaction between multiple functional groups upon absorption is predicted to be a key feature for this broad spectral dependence. This model is in agreement with recent empirical findings and provide a conceptual basis for the further research needed to better constrain the optical properties of light-absorbing aerosols and their environmental impact.

    更新日期:2017-09-21
  • Efficient Thermal Reactions of Sulfur Dioxide on Ice Surfaces at Low Temperature: A Combined Experimental and Theoretical Study
    ACS Earth Space Chem. Pub Date : 2017-09-19
    Jaehyeock Bang, Mahbubul Alam Shoaib, Cheol Ho Choi, Heon Kang
    更新日期:2017-09-20
  • Biological Impacts on Carbon Speciation and Morphology of Sea Spray Aerosol
    ACS Earth Space Chem. Pub Date : 2017-09-19
    Don Q. Pham, Rachel Elizabeth O'Brien, Matthew Fraund, Daniel Bonanno, Olga Laskina, Charlotte Beall, Kathryn A Moore, Sara Forestieri, Xiaofei Wang, Christopher Lee, Camille M Sultana, Vicki H. Grassian, Christopher David Cappa, Kimberly Ann Prather, Ryan C. Moffet

    Sea spray aerosol (SSA) can have complex carbon speciation that is affected by biological conditions in the seawater from which it originates. Biologically-derived molecules can also interact with other, longer-lived, organic and inorganic carbon species in the sea surface microlayer and in the process of bubble bursting. An isolated wave channel facility was used to generate sea spray aerosol during a one month mesocosm study. Two consecutive phytoplankton blooms occurred and sea spray aerosol were sampled throughout. Scanning Transmission X-Ray Microscopy coupled with Near Edge X-Ray Absorption Fine Structure (STXM-NEXAFS) spectroscopy was used to determine spatially resolved carbon speciation within individual particles from 0.18 to 3.2 µm. During phytoplankton blooms, coarse mode particles exhibited an increased abundance of carboxylic acid rich needle-like structures. The extent of organic enrichment in fine mode particles correlates with the occurrence of aliphatic-rich organic species as detected by an intense C1s→σ(C-H)* excitation. These aliphatic-rich species had a strong association with graphitic carbon, detected by a C1s→σ* exciton excitation. This enrichment was unique to particles collected in the aerodynamic size range 0.18-0.32 µm and corresponded with the decrease in hygroscopicity. Aliphatic organics can significantly suppress the particle hygroscopicity when they replace salt, thus influencing the effect sea spray aerosol has on light scattering and cloud formation. These results suggest that graphitic carbon is concentrated in the sea surface microlayer (SSML) during phytoplankton blooms and released through wave action. These results may have implications for radiative transfer and carbon cycling in the ocean-atmosphere system.

    更新日期:2017-09-20
  • Mercury Pollution in Amapá, Brazil: Mercury Amalgamation in Artisanal and Small-Scale Gold Mining or Land-Cover and Land-Use Changes?
    ACS Earth Space Chem. Pub Date : 2017-09-19
    Rebecca Adler Miserendino, Jean Remy Davée Guimarães, Gary Schudel, Sanghamitra Ghosh, José Marcus Godoy, Ellen K. Silbergeld, Peter S.J. Lees, Bridget A. Bergquist

    Mercury (Hg) poses a public health burden in the Amazon and worldwide. Although usually attributed to Hg used in artisanal and small-scale gold mining (ASGM), the primary source of elevated Hg in Amazonian aquatic ecosystems is contested since there have not been tools to differentiate between Hg from ASGM and Hg from other sources such as increased soil erosion associated with land-cover and land-use change. To directly assess Hg contamination from ASGM, stable Hg isotope analyses were applied to sediment cores, surface sediments, and soils from two aquatic ecosystems in Amapá, Brazil, one downstream of ASGM activities and one isolated from ASGM. Downstream of the ASGM sites, the Hg isotope data is consistent with elevated Hg coming dominantly from increased erosion of soils and not from Hg used during gold extraction. Although these two sources represent different pathways of contamination to downstream ecosystems, ASGM may contribute to both land-cover and land-use change and local contamination of soils. Accordingly, these findings demonstrate that in some regions of the Amazon effective Hg mitigation strategies need to address land-use practices in addition to ASGM.

    更新日期:2017-09-20
  • Effects of Pressure on Model Compounds of Meteorite Organic Matter
    ACS Earth Space Chem. Pub Date : 2017-09-13
    Christian Potiszil, Wren Montgomery, Mark A. Sephton
    更新日期:2017-09-14
  • Optical Properties of Airborne Soil Organic Particles
    ACS Earth Space Chem. Pub Date : 2017-09-08
    Daniel P. Veghte, Swarup China, Johannes Weis, Libor Kovarik, Mary K. Gilles, Alexander Laskin

    The impact of water droplets on soils has recently been found to drive emissions of airborne soil organic particles (ASOP). The Chemical composition of ASOP include macromolecules such as polysaccharides, tannins, and lignin (derived from degradation of plants and biological organisms), which determine light absorbing (brown carbon) particle properties. Optical properties of ASOP were inferred from the quantitative analysis of the electron energy-loss spectra acquired over individual particles using transmission electron microscopy. The optical constants of ASOP are compared with those measured for laboratory generated particles composed of Suwanee River Fulvic Acid (SRFA) reference material, which is used as a laboratory surrogate of ASOP. The chemical composition of the particles was analyzed using energy dispersive x-ray spectroscopy, electron energy-loss spectroscopy, and synchrotron-based scanning transmission x-ray microscopy with near edge x-ray absorption fine structure spectroscopy. ASOP and SRFA exhibit similar carbon composition, with minor differences in other elements present. When ASOP are heated to 350 °C their absorption increases as a result of pyrolysis and partial volatilization of semi-volatile organic constituents. The retrieved refractive index (RI) at 532 nm of SRFA particles, ASOP, and heated ASOP were 1.22-0.07i, 1.29-0.07i, and 1.90-0.38i, respectively. Retrieved imaginary part of the refractive index of SRFA particles derived from EELS measurements was higher and the real part was lower compared to data from more common optical methods. Therefore, corrections to the EELS data are needed for incorporation into models. These measurements of ASOP optical constants confirm that they have properties characteristic of atmospheric brown carbon and therefore their potential effects on the radiative forcing of climate need to be assessed in atmospheric models.

    更新日期:2017-09-08
  • Efficient Thermal Reactions of Sulfur Dioxide on Ice Surfaces at Low Temperature: A Combined Experimental and Theoretical Study
    ACS Earth Space Chem. Pub Date : 2017-09-06
    Jaehyeock Bang, Mahbubul Alam Shoaib, Cheol Ho Choi, Heon Kang

    The interaction of sulfur dioxide (SO2) gas with a crystalline ice surface at low temperature was studied by analyzing the surface species with low energy sputtering (LES) and reactive ion scattering methods, and the desorbing gases with temperature-programmed desorption mass spectrometry. The study gives direct evidence for the occurrence of efficient hydrolysis of SO2 with low energy barriers on the ice surface. Adsorbed SO2 molecules react with the ice surface at temperatures above ~90 K to form anionic molecular species, which were detected by OH–, SO2–, and HSO3– emission signals in the LES experiments. Heating the sample above ~120 K causes the desorption of SO2 gas from the surface-bound hydrolysis products. As a result, the hydrolysis of SO2 on an ice surface is most efficient at 100–120 K. The surface products formed at these temperatures correspond to metastable states, which are kinetically isolated on the cold surface. Quantum mechanical calculations of a model ice system suggest plausible mechanistic pathways for how physisorbed SO2 is transformed into chemisorbed HSO3– species. HSO3– is formed either by direct conversion of physisorbed SO2 or through the formation of a stable H2SO3 surface complex, both involving proton transfers on the ice surface with low energy barriers. These findings suggest the possibility that thermal reactions of SO2 occur efficiently on the ice surface of Jovian satellites, even without bombardment by high-energy radiation.

    更新日期:2017-09-07
  • Photochemistry of Products of the Aqueous Reaction of Methylglyoxal with Ammonium Sulfate
    ACS Earth Space Chem. Pub Date : 2017-09-01
    Paige K Aiona, Hyun Ji (Julie) Lee, Renee Leslie, Peng Lin, Alexander Laskin, Julia Laskin, Sergey A. Nizkorodov

    Aqueous reactions of methyl glyoxal (MG) and glyoxal with ammonium sulfate (AS) produce light-absorbing compounds (chromophores) and may serve as a source of atmospheric secondary “brown carbon” (BrC). The molecular composition of these chromophores is ambiguous and their transformation due to exposure to solar UV radiation is not well understood. We examined the molecular composition, mass absorption coefficients, and fluorescence spectra of BrC samples produced by the evaporation of aqueous MG/AS solutions. Chromatograms of BrC produced by evaporation were different from those of BrC produced by slow MG/AS reaction in water, highlighting the substantial sensitivity of BrC to its formation conditions. The BrC samples were characterized before and after their exposure to broadband (270-390 nm) UV radiation. Irradiation led to rapid photobleaching, a decrease in the characteristic 280 nm absorption band, a complete loss of fluorescence, and a dramatic change in molecular composition. By comparing the composition before and after the irradiation, we identified several structural motifs that may contribute to the light absorbing properties of MG/AS BrC. For example, a family of oligomers built from an imidazole carbonyl and repetitive MG units was prominent in the initial sample, and decreased in abundance after photolysis. More complex oligomers containing both imidazole and pyrrole rings in their structures also appeared to contribute to the pool of BrC chromophores. The selective reduction of carbonyl functional groups by sodium borohydride diminished the absorption, but had little effect on the fluorescence of MG/AS BrC samples, suggesting that absorption in this system is dominated by individual chromophores as opposed to supramolecular charge-transfer complexes. Due to the efficient photolysis of the BrC chromophores, this MG/AS BrC system has limited impact on the direct radiative forcing of climate, but may have an effect on atmospheric photochemistry in aerosol particles.

    更新日期:2017-09-04
  • The Effects of Pressure on Model Compounds of Meteorite Organic Matter.
    ACS Earth Space Chem. Pub Date : 2017-08-28
    Christian Potiszil, Wren Montgomery, Mark A. Sephton

    Extraterrestrial organic matter has been widely studied; however, its response to pressure has not. Primitive organic matter bearing meteorites, such as CI and CM carbonaceous chondrites, have experienced variable pressures, up to 10 GPa. To appreciate the effects of these pressures on the organic content of these bodies, the model compounds isophthalic acid, vanillin and vanillic acid were subjected to pressures of up to 11.5 GPa and subsequently decompressed. High resolution synchrotron source Fourier Transform Infrared (FTIR) was used to determine the effects of different benzene substituents at high pressure on both the vibrational assignments of the benzene core of the molecules and the ability of the aromatic compounds to form intermolecular hydrogen bonds. The presence of additional peaks at high pressure was found to coincide with molecules that contain carboxyl groups, these features are interpreted as C-H---O intermolecular hydrogen bonds. The formation of these hydrogen bonds has implications for the origination of macromolecular organic matter (MOM), owing to the importance of such attractive forces during episodes of cross linking, such as esterification. Pressure-induced hydrogen bond formation is a process by which aromatic MOM precursors could have cross linked to generate the organic polymers found within extraterrestrial bodies today.

    更新日期:2017-08-29
  • High Abundance of Fluorescent Biological Aerosol Particles in Winter in Beijing, China
    ACS Earth Space Chem. Pub Date : 2017-08-25
    Siyao Yue, Hong Ren, Songyun Fan, Lianfang Wei, Jian Zhao, Mengying Bao, Shengjie Hou, Jianqiong Zhan, Wanyu Zhao, Lujie Ren, Mingjie Kang, Linjie Li, Yanlin Zhang, Yele Sun, Zifa Wang, Pingqing Fu
    更新日期:2017-08-26
  • Fluid-Enhanced Coarsening of Mineral Microstructures in Hydrothermally Synthesized Bornite–Digenite Solid Solution
    ACS Earth Space Chem. Pub Date : 2017-08-23
    Jing Zhao, Joël Brugger, Benjamin A. Grguric, Yung Ngothai, Allan Pring
    更新日期:2017-08-23
  • Microscopic and Spectroscopic Insights into Uranium Phosphate Mineral Precipitated by Bacillus Mucilaginosus
    ACS Earth Space Chem. Pub Date : 2017-08-22
    Wenbo Huang, Wencai Cheng, Xiaoqin Nie, Faqin Dong, Congcong Ding, Mingxue Liu, Zheng Li, Tasawar Hayat, Njud S. Alharbi
    更新日期:2017-08-23
  • Thermodynamic Constraints on the Lower Atmosphere of Venus
    ACS Earth Space Chem. Pub Date : 2017-08-21
    Nathan S. Jacobson, Michael Kulis, Brandon Radoman-Shaw, Ralph Harvey, Dwight L. Myers, Laura Schaefer, Bruce Fegley
    更新日期:2017-08-22
  • High Abundance of Fluorescent Biological Aerosol Particles in Winter Beijing, China
    ACS Earth Space Chem. Pub Date : 2017-08-16
    Siyao Yue, Hong Ren, Songyun Fan, Lianfang Wei, Jian Zhao, Mengying Bao, Shengjie Hou, Jianqiong Zhan, Wanyu Zhao, Lujie Ren, Mingjie Kang, Linjie Li, Yanlin Zhang, Yele Sun, Zifa Wang, Pingqing Fu

    Primary biological aerosol particles (PBAP) such as pollen, fungal spore, bacteria and virus represent a major subset of particulate matter for both coarse and fine aerosols. Although PBAP affect climate and human health, large uncertainty of their sources and characteristics still remains, especially in urban atmosphere. Here we combined online fluorescent biological aerosol particle measurements and offline fluorescent and biomarker analysis in winter Beijing, a city suffering from severe air pollution. Our results show that the abundance of fluorescent biological particles was higher than many other natural environments. Bioaerosol loadings were much enhanced during mealtime, indicating local emissions of bioaerosols from human activities. The contributions of fungal spore to total organic carbon (OC) from fluorescent bioaerosol analyses were estimated to be around 10% both in clean and polluted periods. This study highlights the importance of human activities to emit bioaerosols into the atmosphere and the potential uncertainties of modeling bioaerosol effects in climate systems.

    更新日期:2017-08-17
  • Abiotic Nitrogen Cycle
    ACS Earth Space Chem. Pub Date : 2017-08-16
    Timothy A. Doane
    更新日期:2017-08-16
  • Study of Iron-Bearing Dolomite Dissolution at Various Temperatures: Evidence for the Formation of Secondary Nanocrystalline Iron-Rich Phases on the Dolomite Surface
    ACS Earth Space Chem. Pub Date : 2017-08-16
    Mathieu Debure, Pascal Andreazza, Aurélien Canizarès, Sylvain Grangeon, Catherine Lerouge, Paul Mack, Benoît Madé, Patrick Simon, Emmanuel Veron, Fabienne Warmont, Marylène Vayer
    更新日期:2017-08-16
  • Molecular Evolution of N-Containing Cyclic Compounds in the Parent Body of the Murchsion Meteorite.
    ACS Earth Space Chem. Pub Date : 2017-08-14
    Hiroshi Naraoka, Yohei Yamashita, Mihoko Yamaguchi, François-Régis Orthous-Daunay

    Primitive meteorites contain various classes of organic compounds. Since the molecular distribution is not fully clarified in meteorites, the comprehensive formation mechanism(s) of extraterrestrial organic compounds have not yet been understood. In this study, diverse and abundant alkylated homologues of N-containing cyclic compounds were identified in the methanol extract of the Murchison meteorite by electrospray ionization using high performance liquid chromatography/ultrahigh resolution mass spectrometry. More than 600 positive ions were assigned to CnHmN+ and CnHmN2+, in which saturated and unsaturated alkylated pyridines and alkylimidazoles are predominant. Both can be synthesized from aldehydes and ammonia through aldol condensation and imine formation under an alkaline environment. Further redox reactions could have proceeded to make these molecules evolve to various CHN compounds including alkylpiperidines and pyridine carboxylic acids. This study indicates that aldol condensation and formose reaction with ammonia is an important mechanism for molecular evolution of N-containing compounds in the asteroid.

    更新日期:2017-08-14
  • Microscopic and Spectroscopic Insights into Uranium Phosphate Mineral Precipitated by Bacillus Mucilaginosus
    ACS Earth Space Chem. Pub Date : 2017-08-11
    Wenbo Huang, Wencai Cheng, Xiaoqin Nie, Faqin Dong, Congcong Ding, Mingxue Liu, Zheng Li, Tasawar Hayat, Njud S. Alharbi

    In this paper, we used spectroscopic and microscopic techniques to investigate the interaction mechanism between uranium and Bacillus mucilaginosus. According to Scanning Electron Microscope couple with Energy Dispersive X-ray Detector (SEM-EDX) analysis, the lamellar uranium phosphate precipitation was only observed on the living B. mucilaginosus and the resting B. mucilaginosus. The Fourier Transform Infrared Spectroscopy (FT-IR) spectrum also indicated the important role of phosphate groups in forming U(VI)-phosphates precipitation. The X-Ray Diffraction (XRD) analysis identified the phase of U(VI)-phosphate precipitation as H3OUO2PO4·3H2O. Batch experiment showed that biominerilization amount could be up to 195.84 mg/g when exposing living B. mucilaginosus to U(VI) aqueous solution at pH 5.0 for 1 h. The precipitate was further evidenced by extended X-ray absorption fine structure (EXAFS) spectra based on the presence of U-P shell, which demonstrated that hydrogen uranyl phosphate (HUP) became the main products on the living B. mucilaginosus with prolonged reacting time. After ashing and hydrothermal process, the precipitated U(VI) on B. mucilaginosus could be converted into UO2 and K(UO2)(PO4)·3H2O. Our findings have significant implications in elucidating the potential role of bacteria in the migration of uranium in geological environment.

    更新日期:2017-08-11
  • Atom Tunneling in the Water Formation Reaction H2 + OH → H2O + H on an Ice Surface
    ACS Earth Space Chem. Pub Date : 2017-08-10
    Jan Meisner, Thanja Lamberts, Johannes Kästner
    更新日期:2017-08-10
  • Photomicrobial Visible Light-Induced Magnetic Mass Independent Fractionation of Mercury in a Marine Microalga
    ACS Earth Space Chem. Pub Date : 2017-08-09
    K. Kritee, Laura C. Motta, Joel D. Blum, Martin Tsz-Ki Tsui, John R. Reinfelder
    更新日期:2017-08-10
  • Hydration Is the Key for Gold Transport in CO2–HCl–H2O Vapor
    ACS Earth Space Chem. Pub Date : 2017-08-08
    Yuan Mei, Weihua Liu, Joël Brugger, Art A. Migdisov, A. E. Williams-Jones
    更新日期:2017-08-09
  • Fluid enhanced coarsening of mineral microstructures in hydrothermally synthesized bornite-digenite solid solution
    ACS Earth Space Chem. Pub Date : 2017-08-07
    Jing Zhao, Joël Brugger, Benjamin A. Grguric, Yung Ngothai, Allan Pring

    Symplectic microstructures are abundant in copper-iron-sulfide minerals and are conventionally considered to form by solid-state diffusion processes. Here we experimentally demonstrate that coarsening of exsolution lamellae occurs 2,500 times faster in the presence of fluid compared to the equivalent dry system. Bornite-digenite solid solutions (Cu5FeS4-Cu8.52Fe0.11S4.88) were synthesized hydrothermally via the replacement of chalcopyrite, and we compared the micro-textures in the product submitted to different cooling histories: (i) cooling to an annealing temperature during hydrothermal synthesis; (ii) dry annealing post synthesis; and (iii) annealing in a hydrothermal fluid following quenching and reheating. Our results indicate that, in the presence of a fluid phase, rapid coarsening of the exsolution lamellae is driven by recrystallization associated with healing of the open porous microstructure in the sulfide. This is accompanied by coalescence of the porosity and its migration to lamella and grain boundaries. As a result, the final microstructure and the kinetics of textural coarsening depend upon the crystallization and cooling history of the parent mineral. Such fluid-driven textural evolution may be a major mode of reaction in ore systems, and is likely to affect oxide and silicate systems alike in the presence of aqueous fluids.

    更新日期:2017-08-07
  • Thermodynamic Constraints on the Lower Atmosphere of Venus
    ACS Earth Space Chem. Pub Date : 2017-08-04
    Nathan S. Jacobson, Michael J. Kulis, Brandon Radoman-Shaw, Ralph Harvey, Dwight L Myers, Laura Schaefer, Bruce Fegley

    The lower Venusian atmosphere is the region from the surface to the cloud deck or about 0-50 km. Early modeling studies of the atmosphere were primarily based on thermodynamics; more recent modeling studies are based on kinetics of the elementary reactions. In this paper we take the accepted nominal composition of near-surface gases at ~42 km and show some of the constituents are indeed at thermodynamic equilibrium. We impose a small oxygen gradient and use a thermodynamic free energy minimization code to describe the vertical gradients of mixing ratios for the primary gases in the lower atmosphere. The oxygen gradient is within the measurement errors on oxygen and thus preserves mass conservation. Reasonable agreement is found between our calculations and the vertical profiles of H2O, H2SO4, OCS, H2S, and Sn (n=1-8). We then did a kinetic analysis of kinetic expressions for the formation of these species. Consistent with other investigators, we find that very few, if any reactions should be at equilibrium in the lower atmosphere. Yet our equilibrium calculations do show some agreement with observations. We conclude that the available kinetic expressions likely need improvement and factors such as catalysis must be included to reflect actual Venus conditions.

    更新日期:2017-08-05
  • Reaction Kinetics of CaOH with H and O2 and O2CaOH with O: Implications for the Atmospheric Chemistry of Meteoric Calcium
    ACS Earth Space Chem. Pub Date : 2017-08-04
    Juan Carlos Gomez Martin, John M. C. Plane
    更新日期:2017-08-04
  • A New Mechanism of Guanine-Isomer Formation from Species Previously Observed in the Interstellar Medium
    ACS Earth Space Chem. Pub Date : 2017-08-03
    João Bosco P. da Silva, Ana Paula M. de Araujo
    更新日期:2017-08-04
  • Study of iron-bearing dolomite dissolution at various temperatures: Evidence for the formation of secondary nanocrystalline iron-rich phases on the dolomite surface
    ACS Earth Space Chem. Pub Date : 2017-08-02
    Mathieu Debure, Pascal Andreazza, Aurélien Canizarès, Sylvain Grangeon, Catherine Lerouge, Paul Mack, Benoit Madé, Patrick Simon, Emmanuel Véron, Fabienne Warmont, Marylene Vayer

    We investigated the dissolution of a natural Fe-containing dolomite [Ca1.003Mg0.972Fe0.024Mn0.002(CO3)2] under acidic conditions (pH 3-5.5) with atomic force microscopy (AFM) at 20 °C, and with batch dissolution experiments at 80 °C. Dolomite dissolution proceeded by two identified mechanisms: removal of dolomite layers through spreading and coalescence of etch pits nucleated at defect points, and stepped retreat from surface edges. The dolomite dissolution rate increased when pH decreased (from 0.410 nm s-1 at pH 3 to 0.035 nm s-1 at pH 5). Rates calculated from edge retreat (vedges) and from etch-pit spreading rates (vsum) were consistent; the etch-pit digging rate was almost 10 times slower than its spreading rate. Nanocrystalline secondary phases precipitated in the course of dolomite dissolution at pH 3 and 80 °C were identified as (nano)hematite, ferrihydrite and an ankerite like mineral using X-ray diffraction, transmission electron microscopy, MicroRaman and X-ray photoelectron spectrometry. In addition, Mg enrichment of the surface layer was observed at 80 °C. The characterizations performed at a nanocrystalline scale highlighted the role played by impurities in the dolomite dissolution/precipitation scheme and evidenced that the preponderant mechanism explaining the incongruent dolomite dissolution is secondary phase precipitation from major and minor elements initially present in the pristine dolomite.

    更新日期:2017-08-03
  • Forsterite Surfaces as Models of Interstellar Core Dust Grains: Computational Study of Carbon Monoxide Adsorption
    ACS Earth Space Chem. Pub Date : 2017-07-31
    Lorenzo Zamirri, Marta Corno, Albert Rimola, Piero Ugliengo
    更新日期:2017-07-31
  • Tunneling Isomerizations on the Potential Energy Surfaces of Formaldehyde and Methanol Radical Cations
    ACS Earth Space Chem. Pub Date : 2017-07-27
    J. Philipp Wagner, Marcus A. Bartlett, Wesley D. Allen, Michael A. Duncan
    更新日期:2017-07-28
  • Atom Tunneling in the Water Formation Reaction H2 + OH → H2O + H on an Ice Surface
    ACS Earth Space Chem. Pub Date : 2017-07-25
    Jan Meisner, Thanja Lamberts, Johannes Kästner

    OH radicals play a key role as an intermediate in the water formation chemistry of the interstellar medium. For example the reaction of OH radicals with H2 molecules is among the final steps in the astrochemical reaction network starting from O, 2 , and O3 . Experimentally it was shown that even at 10 K this reaction occurs on ice surfaces. As the reaction has a high activation energy only atom tunneling can explain such experimental findings. In this study we calculated reaction rate constants for the title reaction on a water-ice Ih surface. To our knowledge, low-temperature rate constants on a surface are not available in the literature. All surface calculations were done using a quantum mechanics/molecular mechanics framework (BHLYP/TIP3P) after a thorough benchmark of different density functionals and basis sets to highly accurate correlation methods. Reaction rate constants are obtained using instanton theory which takes atom tunneling into account inherently, with constants down to 110 K for the Eley–Rideal mechanism and down to 60 K for the Langmuir–Hinshelwood mechanism. We found that the reaction is nearly temperature independent below 80 K. We give kinetic isotope effects for all possible deuteration patterns for both reaction mechanisms. For the implementation in astrochemical networks, we also give fit parameters to a modified Arrhenius equation. Finally, several different binding sites and binding energies of OH radicals on the Ih surface are discussed and the corresponding rate constants are compared to the gas-phase case.

    更新日期:2017-07-26
  • Photo-microbial visible light-induced magnetic mass independent fractionation of mercury in a marine microalga
    ACS Earth Space Chem. Pub Date : 2017-07-24
    Kritee Kritee, Laura C. Motta, Joel D. Blum, Martin Tsz-Ki Tsui, John R Reinfelder

    Methylmercury (MeHg), a highly neurotoxic substance, accumulates in aquatic food webs and is enriched in odd isotopes (i.e., 199Hg and 201Hg), purportedly as a result of abiotic photo-degradation in surface waters. Here, we highlight the potential role of phytoplankton in the mass independent fractionation (MIF) of MeHg in marine food-webs by providing evidence of 1) degradation of intracellular MeHg and reduction of intracellular inorganic mercury (Hg(II)) in the marine microalga, Isochrysis galbana; 2) a large, positive MIF (Δ199Hgreactant - Δ199Hgproduct ~5-10‰) during intracellular degradation of MeHg in cells exposed to visible light with no UVB, suggesting a role in consistent with the accumulation of odd isotope-enriched MeHg in marine food-webs; and 3) a negative MIF (-1‰) during intracellular reduction of Hg(II) in the presence of UVB light. If representative of the photochemical reactivity of MeHg in marine phytoplankton, our results indicate that algal cell-mediated demethylation of MeHg by visible light could account for 20 to 55% of the total photochemically-driven demethylation in the open ocean and transparent freshwater ecosystems with deep euphotic zones. Thus, our results extend the importance of phytoplankton (and possibly other light permeable microorganisms) in mercury biogeochemistry beyond their role as accumulators of MeHg and/or reducers of Hg(II) at the base of the food chain, to their role as important drivers ofinclude MeHg degradation and MIF of Hg in sunlit layers of the ocean and other aquatic systems.

    更新日期:2017-07-25
  • Hydration is the Key for Gold Transport in CO2-HCl-H2O Vapor
    ACS Earth Space Chem. Pub Date : 2017-07-21
    Yuan Mei, Weihua Liu, Joël Brugger, Art A Migdisov, Anthony E. Williams-Jones

    Carbon dioxide (CO2) is a major component of volcanic gases and ore-forming hydrothermal fluids. However, CO2 has contrasting effects on the speciation of different metal complexes and on ore mineral solubility, but a molecular understanding of its effects is lacking. To address this deficiency, we conducted ab initio molecular dynamic (MD) simulations of the behavior of AuCl(aq) in the CO2-H2O system at 340 ºC, 118-152 bar, and 800 ºC, 265-291 bar for CO2 mole fractions (XCO2) of 0.1-0.9. The MD simulations indicate that the linear [H2O-Au-Cl]0 structure of gold chloride is not affected by CO2 at XCO2 up to 0.8 at 340 ºC and up to 0.5 at 800 ºC, whereas the “dry” [AuCl]0 species predominates at XCO2>0.8 at 340 ºC and >0.5 at 800 ºC. The number of water molecules hydrating the AuCl(aq) complex decreases systematically with increasing CO2 mole fraction and increasing temperature. Results of Au solubility experiments at 340 ºC in CO2-H2O solutions show that the addition of CO2 does not enhance Au solubility. We conclude that hydrated chloride species with linear geometry are the main means for transporting gold in CO2-H2O-HCl fluids, and that Au solubility decreases in CO2-bearing hydrothermal fluids as a result of the decrease in hydration of the Au complexes. This contrasts with the behavior of divalent transition metals (e.g., Fe, Co, Ni, and Zn). We propose that the different solubility behavior of Au and base metals are due to the changes in translational entropy as a result of the changes in coordination geometry (and associated hydration) of the complexes with increasing XCO2. The first shell coordination of Au(I) complexes remains constant over wide ranges of XCO2, whereas first-row divalent transition metal complexes undergo entropy-driven geometric changes with decreasing water activity.

    更新日期:2017-07-22
  • Ultraviolet Spectroscopy of the Gas Phase Hydration of Methylglyoxal
    ACS Earth Space Chem. Pub Date : 2017-07-19
    Jay A. Kroll, Anne S. Hansen, Kristian H. Møller, Jessica L. Axson, Henrik G. Kjaergaard, Veronica Vaida
    更新日期:2017-07-20
  • Density Functional Theory Calculation of the Absorption Properties of Brown Carbon Chromophores Generated by Catechol Heterogeneous Ozonolysis
    ACS Earth Space Chem. Pub Date : 2017-07-19
    Ana Catarina O. Magalhães, Joaquim C. G. Esteves da Silva, Luís Pinto da Silva
    更新日期:2017-07-20
  • A new mechanism of guanine-isomer formation from species previously observed in the interstellar medium
    ACS Earth Space Chem. Pub Date : 2017-07-18
    João Bosco Paraíso da Silva, Ana Paula Mesquita de Araujo

    Adenine and guanine have been observed in meteor material. Because of this, they are thought to have been formed in the interstellar medium. However, different from adenine for which there exists several theoretical works exploring the mechanisms of formation, guanine has received minor attention. In this work a retrosynthetic analysis strategy was employed to suggest a new mechanism of guanine formation from species previously observed in the interstellar medium: HCN, CCO, HNCNH and its isomer H2NCN. MP2/6-311++G(2d,2p) calculation were used to evaluate the Gibbs free energy of the minimum and transition state involved in a simple mechanism of reaction, involving only five steps. The intermediate species are highly polar (dipole moment range 4.35 D – 7.72 D), which make them candidates for observation in the rotational spectra. In terms of energy, this new mechanism is very exergonic and the energy barriers are monotonically decreasing. The value of the energy barrier for the first step in this mechanism was substantially reduced when water molecules were explicitly introduced as a way to represent water-ice coated grain surfaces.

    更新日期:2017-07-19
  • Oxidation of Ni-rich mangrove sediments after isolation from the sea (Dumbea Bay, New Caledonia): Fe and Ni behavior and environmental implications
    ACS Earth Space Chem. Pub Date : 2017-07-17
    Vincent Noël, Farid Juillot, Guillaume Morin, Cyril Marchand, Georges Ona-Nguema, Eric Viollier, Francois Prevot, Gabrielle Dublet, Fabien Maillot, Ludovic Delbes, Gregory Marakovic, John R. Bargar, Gordon E. Brown

    Formation of Fe-sulfides in anoxic layers of mangrove sediments makes this ecosystem a potential long-term sink for metal pollutants in the inter-tropical region. Increasing anthropogenic pressure on coastal areas can alter the physico-chemical of mangrove sediments by modifying their redox state, affecting directly the rate of Fe-sulfides that mediate accumulation of metal contaminant. Here, we show that isolation from the sea, due to land use planning, directly modify the redox state of mangrove sediments from reducing condition to oxidizing condition, affecting the stability of Ni-accumulating Fe-sulfides. Unusual suboxic/oxic conditions are indeed observed at intermediate depths in these mangrove sediments and favor the oxidative dissolution of Ni-pyrite (Fe1-xNixS2) that initially formed under anoxic/suboxic conditions. This reaction leads to a significant release of aqueous sulfides, Fe2+ and Ni2+ at the redox boundary. HS- and Fe2+ oxidize into sulfate and Fe(III) and precipitate as schwertmannite (Fe8O8(OH)6SO4), leading to acidification of the pore-waters. Meanwhile, aqueous Ni2+ is mostly leached downward in the underlying anoxic layers of the sediment where it sorbs at the surface of pyrite and Ni-pyrite. These results emphasize the potential of Fe-sulfides for mitigating the impact of the oxidation of former Ni-rich mangrove sediments, as long as the anoxic conditions are preserved at depth. They can be expanded to other divalent metals and should be applicable to a larger set of mangrove ecosystems worldwide.

    更新日期:2017-07-18
  • Forsterite surfaces as models of interstellar core dust grains: computational study of carbon monoxide adsorption
    ACS Earth Space Chem. Pub Date : 2017-07-14
    Lorenzo Zamirri, Marta Corno, Albert Rimola, Piero Ugliengo

    Carbon monoxide (CO) is the second most abundant gas-phase molecule after molecular hydrogen (H2) of the Interstellar Medium (ISM). In Molecular Clouds (MCs), an important component of the ISM, it adsorbs at the surface of core grains, usually made of Mg/Fe silicates, and originates Complex Organic Molecules (COMs) through the catalytic power of active sites at the grain surfaces. To understand the atomistic, energetic and spectroscopic details of the CO adsorption on core grains, we resorted to Density Functional Theory based on the hybrid B3LYP-D* functional inclusive of dispersion contribution. We modeled the complexity of interstellar silicate grains by studying adsorption events on a large set of infinite extended surfaces cut out from the bulk Mg2SiO4 forsterite, the Mg end-member of olivines (Mg2xFe2-2xSiO4), also a very common mineral on Earth crust. Energetic and structural features indicate that CO get exclusively physisorbed, with binding energy values in the 23-68 kJ mol–1 range. Detailed analysis of data revealed that dispersive interactions are relevant together with the important electrostatic contribution due to the quadrupolar nature of the CO molecule. We performed a full thermodynamic treatment of the CO adsorption at the very low temperature typical of the ISM as well as a full spectroscopic characterization of the CO stretching frequency, which we prove to be extremely sensitive to the local nature of the surface-active site of adsorption. We also performed a detailed kinetic analysis of CO desorption from the surface models at different temperatures characterizing the colder regions of the ISM. Our computed data could be incorporated in the various astrochemical models of interstellar grains developed so far and thus contribute to improve the description of the complex chemical network occurring at their surfaces.

    更新日期:2017-07-15
  • Reaction kinetics of CaOH with H and O2, and O2CaOH with O: implications for the atmospheric chemistry of meteoric calcium
    ACS Earth Space Chem. Pub Date : 2017-07-14
    Juan Carlos Gomez Martin, John Maurice Campbell Plane

    The ablation of cosmic dust particles entering the Earth’s upper atmosphere produces a layer of Ca atoms around 90 km. Here we present a set of kinetic experiments designed to understand the nature of the Ca molecular reservoirs on the underside of the layer. CaOH was produced by laser ablation of a Ca target in the fast flow tube, and detected by non-resonant laser induced fluorescence, probing the D(2Σ+)←X(2Σ1) transition at 346.9 nm. The following rate constants were measured (at 298 K): k(CaOH + H → Ca + H2O) = (1.04 ± 0.24) × 10-10 cm3 molecule-1 s-1, k(CaOH + O → CaO + OH) < 1 × 10-11 cm3 molecule 1 s-1 and k(CaOH + O2 → O2CaOH; 1 Torr) = (5.9 ± 1.8) × 10-11 cm3 molecule-1 s-1 (uncertainty at 2σ level of confidence). The recycling of CaOH from reaction between O2CaOH and O proceeds with an effective rate constant of keff(O2CaOH + O → CaOH + products, 298 K) = 〖"2.8" 〗_(-"1.2" )^"+2.0" × 10-10 cm3 molecule-1 s-1). Master equation modelling of the CaOH + O2 kinetics is used to extrapolate to mesospheric temperatures and pressures. The results suggest that formation of O2CaOH slows down the conversion of CaOH to atomic Ca via reaction with atomic H, and O2CaOH is likely to be a long-lived reservoir species on the underside of the Ca layer and a building block of meteoric smoke particles.

    更新日期:2017-07-15
  • Tunneling Isomerizations on the Potential Energy Surfaces of Formaldehyde and Methanol Radical Cations
    ACS Earth Space Chem. Pub Date : 2017-07-13
    J. Philipp Wagner, Marcus A. Bartlett, Wesley D. Allen, Michael A. Duncan

    Formaldehyde (H2CO+) and methanol (H3COH+) radical cations, well-known in mass spectrometry, potentially form from radiative ionization or ion-molecule reactions in the interstellar medium. For both ions, other tautomeric forms exist that are accessible via [1,2]hydrogen shifts involving reaction barriers in excess of 25 kcal∙mol−1. Here, we compute the tunneling rates of the isomerization processes connecting the hydroxymethylene radical cation (HCOH+) to its more stable formaldehyde isomer (H2CO+), and the methanol radical cation (H3COH+) to its methylene oxonium isomer (H2COH2+), using the Wentzel-Kramers-Brillouin (WKB) method at the CCSD(T)/cc-pVQZ//B3LYP/cc-pVTZ level of theory. While hydroxymethylene radical cation features a half-life of over 3500 years and thus represents a potentially observable molecule, methanol radical cation is predicted to decay with a half-life of about four days, and is thus not likely to be present in appreciable quantities in space. We discuss the potential relevance of the hydroxymethylene and methylene oxonium cations for interstellar carbohydrate formation as both species represent potentially reactive, cationic, carbon-centered radicals.

    更新日期:2017-07-14
  • 14C Variation of Dissolved Lignin in Arctic River Systems
    ACS Earth Space Chem. Pub Date : 2017-07-11
    Xiaojuan Feng, Jorien E. Vonk, Claire Griffin, Nikita Zimov, Daniel B. Montluçon, Lukas Wacker, Timothy I. Eglinton
    更新日期:2017-07-11
  • 更新日期:2017-07-11
  • Calcifying Response and Recovery Potential of the Brown Alga Padina pavonica under Ocean Acidification
    ACS Earth Space Chem. Pub Date : 2017-07-03
    David Iluz, Simona Fermani, Michal Ramot, Michela Reggi, Erik Caroselli, Fiorella Prada, Zvy Dubinsky, Stefano Goffredo, Giuseppe Falini
    更新日期:2017-07-11
  • Electron-Induced Chemistry: Preliminary Comparative Studies of Hydrogen Production from Water, Methanol, and Diethyl Ether
    ACS Earth Space Chem. Pub Date : 2017-06-30
    Demian Marchione, Martin R. S. McCoustra
    更新日期:2017-07-11
  • Ultrahigh-Field 25Mg NMR and DFT Study of Magnesium Borate Minerals
    ACS Earth Space Chem. Pub Date : 2017-06-30
    Bing Zhou, Alexandra Faucher, Robert Laskowski, Victor V. Terskikh, Scott Kroeker, Wei Sun, Jinru Lin, Jin-Xiao Mi, Vladimir K. Michaelis, Yuanming Pan
    更新日期:2017-07-11
  • Microbes Facilitate Mineral Deposition in Bioelectrochemical Systems
    ACS Earth Space Chem. Pub Date : 2017-06-26
    A. Gartman, A. Picard, H. C. Olins, N. Sarode, D. R. Clarke, P. R. Girguis
    更新日期:2017-07-11
  • The Potential Role of Criegee Intermediates in Nighttime Atmospheric Chemistry. A Modeling Study
    ACS Earth Space Chem. Pub Date : 2017-06-26
    Daphne Meidan, Steven S. Brown, Yinon Rudich
    更新日期:2017-07-11
  • Single-Particle Extinction and Scattering Method Allows for Detection and Characterization of Aggregates of Aeolian Dust Grains in Ice Cores
    ACS Earth Space Chem. Pub Date : 2017-06-22
    M. A. C. Potenza, L. Cremonesi, B. Delmonte, T. Sanvito, B. Paroli, A. Pullia, G. Baccolo, V. Maggi
    更新日期:2017-07-11
  • Mechanism of Ferric Oxalate Photolysis
    ACS Earth Space Chem. Pub Date : 2017-06-22
    David. M. Mangiante, Richard D. Schaller, Piotr Zarzycki, Jillian F. Banfield, Benjamin Gilbert
    更新日期:2017-07-11
  • Partitioning of HCl Between Concentrated Brines and Supercritical CO2 Under Geologic Reservoir Conditions
    ACS Earth Space Chem. Pub Date : 2017-06-21
    Miroslaw S. Gruszkiewicz, David J. Wesolowski
    更新日期:2017-07-11
  • Core Flooding Experiments and Reactive Transport Modeling of Seasonal Heat Storage in the Hot Deep Gassum Sandstone Formation
    ACS Earth Space Chem. Pub Date : 2017-06-15
    Hanne D. Holmslykke, Claus Kjøller, Ida L. Fabricius
    更新日期:2017-07-11
  • Heterogeneous Interaction of Isoprene with Natural Gobi Dust
    ACS Earth Space Chem. Pub Date : 2017-06-05
    Mohamad N. Zeineddine, Manolis N. Romanias, Vincent Gaudion, Véronique Riffault, Frédéric Thévenet
    更新日期:2017-07-11
  • DFT Calculation of the Absorption Properties of Brown Carbon Chromophores Generated by Catechol Heterogeneous Ozonolysis
    ACS Earth Space Chem. Pub Date : 2017-07-10
    Ana Catarina O. Magalhães, Joaquim C.G. Esteves da Silva, Luís Pinto da Silva

    The effect of light-absorbing atmospheric particles on climate change has been incorporated into climate models, but the absence of brown carbon (BrC) in these models has been leading to significant differences between model predictions and measured data on radiative forcing. Also, little is known regarding the relationship between optical properties and BrC’s chemical compositions. Thus, we have characterized the absorption properties of catechol and known heterogeneous ozonolysis products, with a theoretical approach based on Density Functional Theory (DFT). While catechol presents a weak absorption maximum in the UVC region, other polyaromatic derivatives present an absorption up to six times higher, with biphenyl-2,2’,3,3’-tetraol, biphenyl-3,3’,4,4’,5,5’-hexaol and terphenyl-2’,3,3’,3’’,4,4’’-hexaol presenting the strongest absorption. Moreover, these derivatives now absorb in the UVB and UVA regions, which are types of actinic radiation in the UV region not filtered by atmosphere (contrary to UVC), with terphenyl molecules presenting the highest absorption maximum. Furthermore, the absorption efficiency of these compounds is potentiated in the condensed phase, such as cloud droplets, rain, fogs, and water films, due to a higher degree of electron delocalization. This study provides reliable information regarding the absorption properties of BrC generated by catechol, which is essential for the development of accurate models of climate forcing.

    更新日期:2017-07-11
  • Ultraviolet Spectroscopy of the Gas Phase Hydration of Methylglyoxal
    ACS Earth Space Chem. Pub Date : 2017-07-07
    Jay A. Kroll, Anne Schou Hansen, Kristian H. Møller, Jessica L. Axson, Henrik Grum Kjaergaard, Veronica Vaida

    The gas phase ultraviolet spectrum and stability of 1,1-dihydroxyacetone (the geminal diol of methylglyoxal) are investigated using spectroscopic and computational methods. Experimental gas phase electronic spectra recorded in the ultraviolet-visible range were used to follow the hydration of methylglyoxal. We show that upon the addition of water, methylglyoxal hydrates to form the geminal diol. The electronic spectra of methylglyoxal and its geminal diol conformers were calculated using TD-DFT and LR-CC methods to facilitate experimental peak assignments. The lowest energy electronic transition of the diol is experimentally measured and compared with the results of the theoretical calculations. We find that upon formation of the diol, the lowest-energy transition of methylglyoxal (centered around ~430 nm) vanishes, and the remaining transitions, including the methylglyoxal diol absorptions (λmax = 240 nm), fall outside the available solar actinic flux in the troposphere. This likely has significant impacts on the ultimate fate of methylglyoxal in the atmosphere.

    更新日期:2017-07-11
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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