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  • How could a freshwater swamp produce a chemical signature characteristic of a saltmarsh?
    ACS Earth Space Chem. Pub Date : 2017-11-17
    Terrence A McCloskey, Christopher G. Smith, Kam-biu Liu, Marci Marot, Christian Haller

    Reduction-oxidation (redox) reaction conditions, which are of great importance for the soil chemistry of coastal marshes, can be temporally dynamic. We present a transect of cores from northwest Florida wherein radical post-depositional changes in the redox regime has created atypical geochemical profiles at the bottom of the sedimentary column. The stratigraphy is consistent across the transect, consisting of, bottom upward, carbonate bedrock, a gray clay, an organic mud section, a dense clay layer, and an upper organic mud unit representing the current saltwater marsh. However, the geochemical signature of the lower organic mud unit suggests pervasive redox reactions, although the interval has been identified as representing a freshwater marsh, an unlikely environment for such conditions. Analyses indicate that this discrepancy results from post-depositional diagenesis driven by millennial-scale environmental parameters. Rising sea level that led to the deposition of the capping clay layer, created in anaerobic conditions in the freshwater swamp interval, and isolating it hydrologically from the rest of the sediment column. The subsequent infiltration of marine water into this organic material led to sulfate reduction, the buildup of H2S and FeS, and, first anoxic, and then euxinic conditions, marked by the precipitation of Fe, S and Mo, the hallmark of euxinic conditions. Because this chemical transformation occurred long after the original deposition the geochemical signature does not reflect soil chemistry at the time of deposition and cannot be used to infer syn-depositional environmental conditions, emphasizing the importance of recognizing diagenetic processes in paleoenvironmental studies.

    更新日期:2017-11-19
  • Criegee Intermediate–Alcohol Reactions, A Potential Source of Functionalized Hydroperoxides in the Atmosphere
    ACS Earth Space Chem. Pub Date : 2017-11-14
    Max R. McGillen, Basile F.E. Curchod, Rabi Chhantyal-Pun, Joseph M Beames, Nathan Watson, M Anwar H H. Khan, Laura McMahon, Dudley E. Shallcross, Andrew J. Orr-Ewing

    Ozonolysis, the mechanism by which alkenes are oxidized by ozone in the atmosphere, produces a diverse family of oxidants known as Criegee intermediates (CIs). Using a combination of newly acquired laboratory data and global atmospheric chemistry and transport modelling, we find that the reaction of CIs with alcohols – a reaction that was originally employed to trap these reactive species and provide evidence for the ozonolysis mechanism nearly 70 years ago – is occurring in Earth’s atmosphere and may represent a sizeable source of functionalized hydroperoxides therein. Rate coefficients are reported for the reactions of CH2OO and (CH3)2COO + methanol and that of CH2OO + ethanol. Substitution about the Criegee intermediate is found to have a strong influence over the reaction rate, whereas substitution on the alcohol moiety does not. Although these reactions are not especially rapid, both the precursors to CIs and alcohols have large emissions from the terrestrial biosphere, leading to a high degree of collocation for this chemistry. We estimate that the products of these reactions, the α-alkoxyalkyl hydroperoxides (AAAHs) have a production rate of ~30 Gg yr-1. In order to assess the atmospheric lifetime of AAAHs, we used the nuclear ensemble method to construct a UV absorption spectrum from the four lowest energy conformers identified for a representative AAAH, methoxymethyl hydroperoxide. The computed absorption cross section indicates that these compounds will be lost by solar photolysis, although not so rapidly as to exclude competition from other sinks such as oxidation, thermal decay and aerosol uptake.

    更新日期:2017-11-15
  • 更新日期:2017-11-09
  • Characterization of light-absorbing oligomers from reactions of phenolic compounds and Fe (III)
    ACS Earth Space Chem. Pub Date : 2017-11-07
    Avi Lavi, Peng Lin, Bhaskar Bhaduri, Alexander Laskin, Yinon Rudich

    Phenolic compounds are common constituents of atmospheric aerosols. They form by pyrolysis of lignin and by bio-degradation of plant material and are commonly found in biomass burning plumes, re-suspended soil dust and in anthropogenic secondary organic aerosols (SOA). In this study, we show that reactions of Fe(III), a major constituent of mineral dust, with several phenolic compounds (guaiacol, catechol, syringol, o- and p-cresol) that are common in atmospheric aerosols, result in the formation of water insoluble light-absorbing compounds and reduced Fe(II). The study was conducted under acidic conditions (pH=1-2), relevant for areas impacted by biomass burning, anthropogenic emissions and mineral dust. The reaction products have been characterized using a high performance liquid chromatography coupled to photo diode array and high resolution mass spectrometry detectors , UV-visible spectroscopy, X-ray photoelectron spectroscopy and thermal gravimetric analysis. The major identified chromophores are oligomers of the reaction precursors that efficiently absorb light between 300nm and 500nm. The amounts of oligomers vary significantly between the systems studied. The highest amount was observed for guaiacol and catechol, and the least were detected in the syringol experiments, suggesting that the oligomerization proceeds through carbon-carbon coupling preferred at para- and ortho- positions, coupled to the reduction of Fe(III) to Fe(II). The results suggest that aqueous-phase radical reactions of phenolic compounds may be an efficient source of light-absorbing atmospheric organic compounds (Brown Carbon) that plays important roles in Earth’s radiative forcing on global and regional scales and of quinones that can affect health.

    更新日期:2017-11-08
  • Experiments on Condensation of Calcium Sulfide Grains To Demarcate Environments for the Formation of Enstatite Chondrites
    ACS Earth Space Chem. Pub Date : 2017-11-03
    Kaori Yokoyama, Yuki Kimura, Chihiro Kaito
    更新日期:2017-11-05
  • Impact of Intrinsic Structural Properties on the Hydration of 2:1 Layer Silicates
    ACS Earth Space Chem. Pub Date : 2017-11-03
    Florian Schnetzer, Cliff T. Johnston, Gnanasiri S. Premachandra, Nicolas Giraudo, Rainer Schuhmann, Peter Thissen, Katja Emmerich
    更新日期:2017-11-05
  • Cooperative and Inhibited Adsorption of d-Ribose onto Brucite [Mg(OH)2] with Divalent Cations
    ACS Earth Space Chem. Pub Date : 2017-11-03
    Charlene F. Estrada, Alyssa K. Adcock, Dimitri A. Sverjensky, Robert M. Hazen
    更新日期:2017-11-05
  • Highly Time-Resolved Atmospheric Observations Using a Continuous Fine Particulate Matter and Element Monitor
    ACS Earth Space Chem. Pub Date : 2017-10-30
    Hitoshi Asano, Tomoki Aoyama, Yusuke Mizuno, Yukihide Shiraishi
    更新日期:2017-10-30
  • Heterogeneous Ni- and Cd-Bearing Ferrihydrite Precipitation and Recrystallization on Quartz under Acidic pH Condition
    ACS Earth Space Chem. Pub Date : 2017-10-30
    Chong Dai, Mingxi Lin, Yandi Hu

    Ferrihydrite, as one of the most common naturally occurring iron oxides, can sequester toxic metals through coprecipitation. In this study, using grazing-incidence small angle X-ray scattering (GISAXS), the heterogeneous precipitation of pure, Ni-, and Cd- bearing ferrihydrite on quartz were quantified in 0.1 mM Fe3+ solutions in the absence and presence of 1 mM Ni2+ or Cd2+ (pH = 3.8 ± 0.1). Under acidic condition, the limited hydrolysis of metal ions resulted in their small amounts of incorporation in ferrihydrite lattices (< 0.1%), several orders of magnitude lower than those reported at neutral and alkaline pH conditions. The presence of Ni2+ or Cd2+ did not significantly affect the surface charges of either ferrihydrite pre-nucleation clusters (PNCs) or quartz surfaces. Therefore, with similar electrostatic interactions between PNCs and quartz, similar initial heterogeneous precipitation rates of pure, Ni-, and Cd- bearing ferrihydrite on quartz were observed. Later on, continuous heterogeneous nucleation and growth of ferrihydrite nanoparticles resulted in their increased polydispersity, and the size-dependent solubility of ferrihydrite nanoparticles caused the Ostwald ripening process. The presence of Ni and Cd was found to retard the recrystallization of ferrihydrite, probably due to their structural incorporation which could inhibit the dissolution of ferrihydrite. This study provided new kinetic and mechanistic insights for understanding the effects of metal ions on the heterogeneous precipitation and recrystallization processes of ferrihydrite nanoparticles on mineral surfaces, which can better predict the fate and transport of heavy metals.

    更新日期:2017-10-30
  • Experiments on Condensation of Calcium Sulfide Grains to Demarcate Environments for the Formation of Enstatite Chondrites
    ACS Earth Space Chem. Pub Date : 2017-10-24
    Kaori Yokoyama, Yuki Kimura, Chihiro Kaito

    To achieve a better understanding of material evolution in the early solar system, experiments have been performed to constrain the environments in which many of the dust grains formed. Sulfur is an element whose chemical processes and mineralization of related grains are poorly understood. The high reactivity of sulfur makes it difficult to perform experiments in conventional metallic chambers, as these become heavily contaminated. Nevertheless, sulfur is expected to be a key element to understand processes in the early solar system. Here, we performed experiments on the condensation of calcium sulfide (CaS) in a glass chamber in an attempt to identify constraints on the possible formation environments of components of enstatite chondrites in terms of the effects of oxygen. Condensation experiments showed that calcium sulfate (CaSO4) or solid-solution particles of CaS and calcium oxide (CaO), i.e., [Ca(S,O)], were formed at various partial pressures of oxygen. Our results expand the range of possible conditions for the condensation of meteoritic CaS (oldhamite) from a nebula gas and extend the range of environments for the formation of the parent bodies of enstatite chondrites to include those more-oxidizing environments in the solar nebula where the atomic ratio of oxygen to sulfur was less than 6 and where CaS could have incorporated oxygen to form Ca(S,O) without formation of CaSO4.

    更新日期:2017-10-25
  • Cooperative and Inhibited Adsorption of D-Ribose onto Brucite [Mg(OH)2] with Divalent Cations
    ACS Earth Space Chem. Pub Date : 2017-10-24
    Charlene Fae Estrada, Alyssa K Adcock, Dimitri A. Sverjensky, Robert M Hazen

    The adsorption and concentration of sugars onto mineral surfaces in geochemical environments, such as hydrothermal systems, may have influenced the evolution of early life on Earth. We conducted batch adsorption experiments between D-ribose and brucite [Mg(OH)2], a mineral produced from serpentinite-hosted hydrothermal systems, over variable initial ribose concentrations at four ionic strengths resulting from different Mg2+ and Ca2+ ion concentrations in the aqueous phase. Ribose adsorption generally increased with greater initial concentration, and up to 0.3 µmol•m-2 ribose attached onto brucite with 0.6 mM Mg2+ present. Ribose adsorption decreased over six-fold (4.9x10-2 µmol•m-2) when the total Mg2+ ion concentration increased to 5.8 mM. Ribose adsorption increased to 0.4 µmol•m-2 when 4.2 mM CaCl2 was added to the system. Substantial amounts (over 21 µmol•m-2) of dissolved Ca also attached to the brucite surface independent of ribose concentration. We characterized the interactions between ribose, Ca, and the brucite surface by fitting a surface complexation model to adsorption data. We propose three types of surface reactions that were consistent with the experimental data and involve 1) a bidentate outer-sphere or a “standing” ribose surface species, 2) a monodentate Ca-ribose outer-sphere species, and 3) a monodentate Ca outer-sphere species. Our model predicts brucite particle surface charge is negative at low Mg2+ concentrations and further decreases upon the addition of MgCl2, which may hinder our proposed surface complexation of the ribose species, Rib-. We predict that brucite becomes positively-charged with CaCl2 addition, which may be a consequence of the significant extent of Ca adsorption. The increase in ribose adsorption with CaCl2 is likely driven by Ca attachment and the formation of a positively-charged, cooperative Ca-ribose species that our model predicts will predominate over the “standing” ribose species on brucite. Our model of the ribose-brucite system, established by a combination of batch adsorption experiments and surface complexation modeling, has enabled predictions of ribose adsorption over a wide range of pH and complex environmental conditions.

    更新日期:2017-10-25
  • Experimental Evidence for the Formation of Solvation Shells by Soluble Species at a Nonuniform Air–Ice Interface
    ACS Earth Space Chem. Pub Date : 2017-10-23
    Thorsten Bartels-Rausch, Fabrizio Orlando, Xiangrui Kong, Luca Artiglia, Markus Ammann
    更新日期:2017-10-24
  • Impact of Secondary Organic Aerosol Tracers on Tracer-Based Source Apportionment of Organic Carbon and PM2.5: A Case Study in the Pearl River Delta, China
    ACS Earth Space Chem. Pub Date : 2017-10-18
    Qiongqiong Wang, Xiao He, X. H. Hilda Huang, Stephen M. Griffith, Yongming Feng, Ting Zhang, Qingyan Zhang, Dui Wu, Jian Zhen Yu
    更新日期:2017-10-19
  • Crystal-chemical composition of dicoctahedral smectites: an energy-based assessment of empirical relations
    ACS Earth Space Chem. Pub Date : 2017-10-17
    Stephan Kaufhold, Alena Kremleva, Sven Krüger, Notker Roesch, Katja Emmerich, Reiner Dohrmann

    The experimental characterization of various dioctahedral smectites reveals weak correlations between the ratio of cis- and trans-vacant layer structures, the fraction of charge in the tetrahedral sheet, and the iron content. These correlations are demonstrated by two independent sample sets, examined in different laboratories, and hence are considered to be significant. To rationalize and corroborate these relations, accurate relative energies and ion exchange energies of a set of model minerals were determined by quantum chemical density functional calculations. Accordingly, one may trace these empirical correlations mainly back to energy relations and rationalize some deviating smectites by their particular history of formation.

    更新日期:2017-10-17
  • Highly Time-Resolved Atmospheric Observations Using a Continuous PM2.5 and Element Monitor
    ACS Earth Space Chem. Pub Date : 2017-10-12
    Hitoshi Asano, Tomoki Aoyama, Yusuke Mizuno, Yukihide Shiraishi,

    We measured the PM2.5 and element (S, Pb, K, Si, Ca, Fe, Mn, and Zn) concentrations in March 2015 by using a continuous PM2.5 mass and element concentration monitor at Sanyo Onoda city, which is located in the western part of Japan. In addition to the PM2.5 concentration measurements, this instrument can continuously and automatically analyze the elements in the PM2.5 without sample pretreatment by using X-ray fluorescence at a high time resolution. The PM2.5 concentrations measured with our apparatus and the Yamaguchi Prefectural Government’s system had a good correlation, with a correlation coefficient of 0.931. The increase in the PM2.5 concentration in the case of the westerly wind indicates that the air mass includes a high concentration of particulate matter that is transported from the Asian continent. The anthropogenic components (S, Pb, and K) showed a strong correlation with the PM2.5. However, there was a moderate correlation between the crustal components (Si, Ca, and Fe) and the PM2.5. During a high PM2.5 concentration event, the results of the time lag in the peak between the anthropogenic components and the crustal components indicate that the distinct air masses were transported from different origins. The Pb/Zn ratio increased with the PM2.5, which might be a useful indicator for evaluating the long-range transport.

    更新日期:2017-10-13
  • Impact of Secondary Organic Aerosol Tracers on Tracer-based Source Apportionment of Organic Carbon and PM2.5: A Case Study in the Pearl River Delta, China
    ACS Earth Space Chem. Pub Date : 2017-10-06
    Qiongqiong Wang, Xiao He, X. H. Hilda Huang, Stephen Miles Griffith, Yongming Feng, Ting Zhang, Qingyan Zhang, Dui Wu, Jian Zhen Yu

    Knowledge of the relative abundance of primary organic aerosol (POA) and secondary organic aerosol (SOA) forms an important scientific basis for formulating particulate matter (PM) control policies. Taking advantage of a comprehensive chemical composition data set of PM2.5 including both POA and SOA tracers (most notably SOA tracers of a few biogenic voltaic organic compound precursors), we investigate the impact of inclusion of SOA tracers on the source apportionment of organic carbon (OC) and PM2.5 in the Pearl River Delta (PRD) region of China using positive matrix factorization (PMF). In PMF runs incorporating SOA tracers (PMFw), ten PMF factors were resolved including four secondary factors: (1) SOA_I (α-pinene, β-caryophyllene and naphthalene derived SOA), (2) SOA_II (isoprene derived SOA), (3) a secondary sulfate factor, and (4) a secondary nitrate factor. In PMF tests without SOA tracers (PMFwo), the SOA_I and SOA_II factors could not be extracted while the remaining eight source factors were resolved. Among the eight common source factors, the industrial emission factor, identified by high loadings of Zn and Pb, showed the largest variations between PMFw and PMFwo solutions. The source contributions of SOA_I and SOA_II resolved in PMFw were largely shifted to the industry emission source in PMFwo. Secondary organic carbon (SOC) summed from the four secondary factors in PMFw contributed ~40% (4.47 μgC/m3) while the SOC estimate by PMFwo (3.51 μgC/m3) was 21% lower due to the inability in extracting SOA_I and SOA_II. Secondary PM2.5 by PMFwo was 6% lower than that by PMFw (23.7 vs 25.2 μg/m3). The PMFw results indicated that SOC from specific precursors may have different formation pathways than secondary sulfate and nitrate formation processes and their source contributions could not be properly resolved without the indicative tracers included in PMF. This study demonstrates the utility of biogenic SOA tracers in resolving isoprene-derived SOA and highlights the need for more SOA tracers, especially those specific to anthropogenic precursors, in improving the source apportionment for those broad OA sources such as industrial emissions.

    更新日期:2017-10-06
  • 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 : 2017-10-05
    Rebecca Adler Miserendino, Jean Remy Davée Guimarães, Gary Schudel, Sanghamitra Ghosh, José Marcus Godoy, Ellen K. Silbergeld, Peter S. J. Lees, Bridget A. Bergquist
    更新日期:2017-10-05
  • Biological Impacts on Carbon Speciation and Morphology of Sea Spray Aerosol
    ACS Earth Space Chem. Pub Date : 2017-10-03
    Don Q. Pham, Rachel O’Brien, Matthew Fraund, Daniel Bonanno, Olga Laskina, Charlotte Beall, Kathryn A. Moore, Sara Forestieri, Xiaofei Wang, Christopher Lee, Camille Sultana, Vicki Grassian, Christopher D. Cappa, Kimberly A. Prather, Ryan C. Moffet
    更新日期:2017-10-04
  • Impact of Intrinsic Structural Properties on the Hydration of 2:1 Layer Silicates
    ACS Earth Space Chem. Pub Date : 2017-10-03
    Florian Schnetzer, Cliff T Johnston, Gnanasiri S. Premachandra, Nicolas Giraudo, Rainer Schuhmann, Peter Thissen, Katja Emmerich

    Several 2:1 layer silicates comprising di- and trioctahedral smectites of different layer charge between 0.2 to 0.4 per formula unit and a trioctahedral vermiculite were studied by an in-situ method that allowed FTIR spectra and water vapor sorption isotherms to be obtained simultaneously. Particle size and shape of the selected materials were determined using X-ray diffraction (XRD) and gas adsorption analysis, which provided an estimate of the particle size with resulting edge site proportion. The aim of this study was to elucidate the hydration mechanism in 2:1 layer silicates during desorption and adsorption of water vapor. Domains in the de- and adsorption of water vapor of the smectite samples with a slightly increasing slope were explained by a heterogeneous layer charge distribution, which enables the coexistence of different hydration states even under controlled conditions. Whereas hysteresis was observed over the entire isothermal range of the smectites, the isotherm of the vermiculite sample only showed hysteresis in the transition from mono- (1W) to bi-hydrated state (2W). We also revealed that hysteresis is a function of the layer charge distribution, the achieved water content and the particle size with resulting edge site contribution. Increasing the edge site proportions led to an increased hysteresis. The findings from the experimental FTIR/gravimetric analysis showed that the transition from 2W to 1W and backward is visible using IR spectroscopy. The shifting of δ(H-O-H) was influenced by the layer charge and octahedral substitutions. As a final point, we use water as a sensor molecule to describe the OH groups of the octahedral sheet and show that the observed shifts result from a change in the tilting angle. Our experimental results were supported by ab initio thermodynamic simulations that revealed the different shifting behavior of δ(H-O-H) and δ(Mx+-OH-Ny+) related to the differences in surface charge density and octahedral compositions.

    更新日期:2017-10-03
  • Molecular Evolution of N-Containing Cyclic Compounds in the Parent Body of the Murchison Meteorite
    ACS Earth Space Chem. Pub Date : 2017-10-02
    Hiroshi Naraoka, Yohei Yamashita, Mihoko Yamaguchi, François-Régis Orthous-Daunay
    更新日期:2017-10-03
  • Experimental Evidence for the Formation of Solvation Shells by Soluble Species at a Non-Uniform Air – Ice Interface.
    ACS Earth Space Chem. Pub Date : 2017-09-29
    Thorsten Bartels-Rausch, Fabrizio Orlando, Xiangrui Kong, Luca Artiglia, Markus Ammann

    Soluble species induce surface pre-melting at the air – ice interface in the thermodynamic ice stability domain below the liquidus. This quasi-liquid layer is thought to increase in thickness with concentration of impurities and to represent a reservoir into which larger amounts of soluble species dissolve compared to a more rigid ice surface. To directly investigate the response of the quasi-liquid layer to increasing amounts of solutes and to clarify the distribution of these at the ice surface with depth, we use a combination of Auger electron yield X-ray absorption and photoelectron spectroscopies. We studied the adsorption of formic acid to ice at 251 K. These two complimentary methods allow concluding that solutes enter the air – ice interface, but do not necessarily induce a thicker quasi-liquid layer. Rather, modifications of the hydrogen bonding network seem to be linked to the formation of solvation shells and to long-range effects on the hydrogen-bonding network. We suggest that the flexibility of water molecules in the quasi-liquid layer is essential to form solvation shells and interpret the confinement of formic acid to the upper few ice bilayers to be linked with the structure of the hydrogen-bonding network getting more ice-like and rigid with depth at the air – ice interface.

    更新日期:2017-10-01
  • A Model for the Spectral Dependence of Aerosol Sunlight Absorption
    ACS Earth Space Chem. Pub Date : 2017-09-29
    August Andersson
    更新日期:2017-10-01
  • Optical Properties of Airborne Soil Organic Particles
    ACS Earth Space Chem. Pub Date : 2017-09-28
    Daniel P. Veghte, Swarup China, Johannes Weis, Libor Kovarik, Mary K. Gilles, Alexander Laskin
    更新日期:2017-09-29
  • Photochemistry of Products of the Aqueous Reaction of Methylglyoxal with Ammonium Sulfate
    ACS Earth Space Chem. Pub Date : 2017-09-28
    Paige K. Aiona, Hyun Ji Lee, Renee Leslie, Peng Lin, Alexander Laskin, Julia Laskin, Sergey A. Nizkorodov
    更新日期:2017-09-28
  • 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
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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