冬月 世馬

Copyright © 2019 by The Geochemical Society of Japan. We present a numerical study conducted using a regional Lagrangian model to account for the transport, deposition and radioactive decay of 35S in sulfur dioxide and sulfate aerosols emitted into the atmosphere during the Fukushima Daiichi Nuclear Power Plant incident. The model is a Eulerian-Lagrangian hybrid system that accounts for chemical conversion of SO2 into SO42- in a Eulerian manner. The simulations were compared to field measurements of atmospheric 35S in sulfate collected at Kawamata, Tsukuba, Kashiwa, Fuchu and Yokohama, Japan. The 35S emission scenario that best replicated the field measurements followed the same temporal variation pattern as the 134/137Cs emissions. These results suggest that 35S and 134/137Cs follow a similar release pattern. Among the considered emission scenarios, a maximum flux of emitted chemical compounds was assumed to be either 100% 35SO42- or 100% 35SO2, with values of 4.0 \ 1019 molecules/hour and 4.0 \ 1020 molecules/hour, respectively on March 14th. These emission scenarios reflect the findings reported in the literature, where traces of 35SO2 were measured along with 35SO42-, so the actual emission is expected to be a combination of both chemical forms. The Kawamata measurements (Figs. 5 and 6) presented a large concentration in the July–August period, several months after emissions decreased by more than an order of magnitude. To explain this anomaly, re-suspension ratios were calculated for the Kawamata site, which ranged between 0.1 and 1.5% and partially, but not fully, explain the large measured concentrations. Furthermore, they show large discrepancies with 134/137Cs re-suspension values for measurements at the town of Namie. This situation indicates a lack of understanding of the transformations of 35S that occurs after deposition and the mechanisms involved in the 35S re-suspension process.

We introduce a Bayesian method for guiding future directions for detection of life on exoplanets. We describe empirical and theoretical work necessary to place constraints on the relevant likelihoods, including those emerging from better understanding stellar environment, planetary climate and geophysics, geochemical cycling, the universalities of physics and chemistry, the contingencies of evolutionary history, the properties of life as an emergent complex system, and the mechanisms driving the emergence of life. We provide examples for how the Bayesian formalism could guide future search strategies, including determining observations to prioritize or deciding between targeted searches or larger lower resolution surveys to generate ensemble statistics and address how a Bayesian methodology could constrain the prior probability of life with or without a positive detection.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Authors because of a large amount of errors caused by incorrect interpretation of the potential energy curve boundaries by the data processing functions in their close-coupling algorithm, producing incorrect wavefunctions for the continuum region in the absorption spectrum. The spectrum calculated using the incorrect wavefunctions introduced periodic fluctuation in the absorption cross-section seen in the original article, which results in erroneous isotopic fractionation values. The updated spectra calculated after fixing the issues features a smooth continuum band, removing all false artifacts from isotopic effect analysis, producing significantly different results from the ones in this original article. The authors will submit the corrected data in a new article.

The ultra-fast photoisomerization reactions between 1,3-cyclohexadiene (CHD) and 1,3,5-cis-hexatriene (HT) in both hexane and ethanol solvents were revealed by nonadiabatic ab initio molecular dynamics (AI-MD) with a particle-mesh Ewald summation method and our Own N-layered Integrated molecular Orbital and molecular Mechanics model (PME-ONIOM) scheme. Zhu-Nakamura version trajectory surface hopping method (ZN-TSH) was employed to treat the ultra-fast nonadiabatic decaying process. The results for hexane and ethanol simulations reasonably agree with experimental data. The high nonpolar-nonpolar affinity between CHD and the solvent was observed in hexane solvent, which definitely affected the excited state lifetimes, the product branching ratio of CHD:HT, and solute (CHD) dynamics. In ethanol solvent, however, the CHD solute was isomerized in the solvent cage caused by the first solvation shell. The photochemical dynamics in ethanol solvent results in the similar property to the process appeared in vacuo (isolated CHD dynamics). (C)2017 Elsevier B.V. All rights reserved.

Photochemical mechanisms of Sulfur Mass-Independent Fractionation (S-MIF) are still poorly understood. Previous laboratory experiments have indicated that the S-MIF depends largely on the spectrum of the incident light source and the partial pressure of SO2, though the basic character of the Archean S-MIF (Delta S-36/Delta S-33 = similar to - 1) has never been reproduced. We have conducted new photochemical experiments at low pSO(2) (1-10 Pa) conditions under the presence of CO and found a reasonable mechanism to reproduce the Delta S-36/Delta S-33 slope about 1. As previously suggested (Ono et al., 2013), the low pSO(2) is key to studying the self-shielding effect within a range of realistic atmospheric conditions. Also, reducing conditions are critical for simulating the O-2-poor atmosphere, whereas photolysis of pure SO2 provides excess 0 atoms that significantly change the overall chemistry. Our experimental results confirmed that significant S-MIF (Delta S-36/Delta S-33 = -2.4) can be produced by self-shielding in the SO2 photolysis band (185-220 nm), even if the SO2 column density is as low as 10(16) molecules cm(-2). Thus, photolysis within a volcanic plume of similar to 0.1 ppm SO2 is capable of producing a large S-MIF signature. The isotopic fractionations originating from the different absorption cross sections of SO2 isotopologues (i.e. wavelength dependent effect; without self-shielding) are only minor (potentially up to +4%(0) for Delta S-33). Under reducing conditions, however, another S-MIF signal with Delta S-36/Delta S-33 ratio of similar to+0.7 is produced due to collision-induced intersystem crossing (ISC) from singlet to triplet states of SO2 (Whitehill et al., 2013), and should also be transferred into the final product that is responsible for changing the Delta S-36/Delta S-33 slope. Based on a photochemical model of the S-O-C system with the two SMIF-yielding reactions, the largest S-MIF observed in the late Archean Mt. McRae Fm. (Delta S-33 = +9.4%(0), Delta S-36 = -7.5%(0)) can be reproduced by solar UV irradiation of a SO2 column of similar to 6.4 x 10(16) molecules cm(-2) with a sufficiently high concentration of reducing gasses (similar to 2% CO or CH4) where the ISC-derived MIF contributes similar to 3% through the photoexcitation channel initiated in the 240-340 nm region. Our work shows that a photochemical model considering the two major S-MIF-yielding reactions (SO2 + hv -> SO + O and (SO2)-S-1 + M -> (SO2)-S-3 + M) can explain the behavior of the S-MIF observed in laboratory experiments. The combination of the two effects is more important under reducing condition and should be considered to interpret the geological record. (C) 2016 Elsevier B.V. All rights reserved.

A marine ecosystem model that incorporates nitrous oxide (N2O) production processes (i.e., ammonium oxidation during nitrification and nitrite reduction during nitrifier denitrification) and N isotopomers was developed to estimate the sea-air N2O flux and to quantify N2O production processes. This model was applied to water above the depth of 220 m at two contrasting time series sites, a subarctic station (K2) and a subtropical station (S1) in the western North Pacific. The model was validated with observed N concentration and N isotopomer data sets, and successfully simulated the higher N2O concentrations, higher delta N-15 values, and higher site preference values for N2O at K2 compared with S1. The annual mean N2O emissions were estimated to be 32.3 mg N m(-2) year(-1) at K2 and 2.7 mg N m(-2) year(-1) at S1. The results of case studies based on this model estimated the ratios of in situ biological N2O production to nitrate production during nitrification to be similar to 0.22 % at K2 and similar to 0.06 % at S1. It is also suggested that N2O was mainly produced via ammonium oxidation at K2, but was produced via both ammonium oxidation and nitrite reduction at S1. A large fraction (similar to 80 %) of the ammonium oxidation at K2 was carried out by archaea in the subsurface water. Isotope tracer incubation experiments using an archaeal activity inhibitor supported this hypothesis.

The photoisomerization process between 1,3-cyclohexadiene (CHD) and 1,3,5-cis-hexatriene (HT) has been studied by nonadiabatic ab initio molecular dynamics based on trajectory surface-hopping approach with a full-dimensional reaction model. The quantum chemical calculations were treated at MS-MR-CASPT2 level for 8 electrons in 8 orbitals with the cc-pVDZ basis set. The Zhu-Nakamura formula was employed to evaluate nonadiabatic transition probabilities. S-1 and S-2 states were included in the photoisomerization dynamics. Lifetimes and CHD: HT branching ratios were computationally estimated on the basis of statistical analysis of multiple executed trajectories. The analysis of trajectories suggested that the nonadiabatic transitions at the S-0/S-1 and S-1/S-2 conical intersections (CoIn) are correlated to the Kekule-type vibration and the C3-C4-C5 bending motion, respectively. The one-sided branching ratio was obtained by excitations to the S-2 state; 70:30. The critical branching process was found to be dominated by the location of CoIn in potential energy hypersurface of the excited state. (C) 2015 Elsevier B.V. All rights reserved.

Photodissociation dynamics of sulfuric acid after excitation to the first and second excited states (S-1 and S-2) were studied by an on-the-fly ab initio molecular dynamics simulations based on the Zhu-Nakamura version of the trajectory surface hopping (ZN-TSH). Forces acting on the nuclear motion were computed on-the-fly by CASSCF method with Dunning's augmented cc-pVDZ basis set. It was newly found that the parent molecule dissociated into two reaction-channels (i) HSO4(1(2)A'') + H(S-2) by S-1-excitation, and (ii) HSO4(2(2)A'') + H(S-2) by S-2-excitation. The direct dissociation dynamics yield products different from the SO2 + 2OH fragments often presented in the literature. Both channels result in the same product and differs only in the electronic state of the HSO4 fragment. The trajectories running on S-2 do not hop with S-0 and a nonadiabatic transition happens at the S-2-S-1 conical intersection located at a longer OH bond-length than the S-1-S-0 intersection producing an electronic excited state (2(2)A'') of HSO4 product. (C) 2015 Elsevier B.V. All rights reserved.

The ultraviolet absorption cross sections of the SO2 isotopologues are essential to understanding the photochemical fractionation of sulfur isotopes in planetary atmospheres. We present measurements of the absorption cross sections of (SO2)-S-32, (SO2)-S-33, (SO2)-S-34, and (SO2)-S-36, recorded from 190 to 220nm at room temperature with a resolution of 0.1nm (25cm(-1)) made using a dual-beam photospectrometer. The measured absorption cross sections show an apparent pressure dependence and a newly developed analytical model shows that this is caused by underresolved fine structure. The model made possible the calculation of absorption cross sections at the zero-pressure limit that can be used to calculate photolysis rates for atmospheric scenarios. The (SO2)-S-32, (SO2)-S-33, and (SO2)-S-34 cross sections improve upon previously published spectra including fine structure and peak widths. This is the first report of absolute absorption cross sections of the (SO2)-S-36 isotopologue for the (CB2)-B-1-X(1)A(2) band where the amplitude of the vibrational structure is smaller than the other isotopologues throughout the spectrum. Based on the new results, solar UV photodissociation of SO2 produces (34)epsilon, (33), and (36) isotopic fractionations of +4.611.6, +8.89.0, and -8.8 +/- 19.6 parts per thousand, respectively. From these spectra isotopic effects during photolysis in the Archean atmosphere can be calculated and compared to the Archean sedimentary record. Our results suggest that broadband solar UV photolysis is capable of producing the mass-independent fractionation observed in the Archean sedimentary record without involving shielding by specific gaseous compounds in the atmosphere including SO2 itself. The estimated magnitude of (33), for example, is close to the maximum S-33 observed in the geological record.

Natural climate variation, such as that caused by volcanoes, is the basis for identifying anthropogenic climate change. However, knowledge of the history of volcanic activity is inadequate, particularly concerning the explosivity of specific events. Some material is deposited in ice cores, but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions. Stable sulfur isotope abundances contain additional information, and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass-independent anomalies in sulfur isotopes in glacial sulfate. We describe a mechanism, photoexcitation of SO2, that links the two, yielding a useful metric of the explosivity of historic volcanic events. A plume model of S(IV) to S(VI) conversion was constructed including photochemistry, entrainment of background air, and sulfate deposition. Isotopologue-specific photoexcitation rates were calculated based on the UV absorption cross-sections of (32)SO2, (33)SO2, (34)SO2, and (36)SO2 from 250 to 320 nm. The model shows that UV photoexcitation is enhanced with altitude, whereas mass-dependent oxidation, such as SO2 + OH, is suppressed by in situ plume chemistry, allowing the production and preservation of a mass-independent sulfur isotope anomaly in the sulfate product. The model accounts for the amplitude, phases, and time development of Δ(33)S/δ(34)S and Δ(36)S/Δ(33)S found in glacial samples. We are able to identify the process controlling mass-independent sulfur isotope anomalies in the modern atmosphere. This mechanism is the basis of identifying the magnitude of historic volcanic events.

The sulfur kinetic isotope effect (KIE) in the reaction of carbonyl sulfide (OCS) with O(P-3) was studied in relative rate experiments at 298 +/- 2 K and 955 +/- 10 mbar. The reaction was carried out in a photochemical reactor using long path FTIR detection, and data were analyzed using a nonlinear least-squares spectral fitting procedure with line parameters from the HITRAN database. The ratio of the rate of the reaction of (OCS)-S-34 relative to (OCS)-S-32 was found to be 0.9783 +/- 0.0062 ((34)epsilon = (-21.7 +/- 6.2)parts per thousand). The KIE was also calculated using quantum chemistry and classical transition state theory; at 300 K, the isotopic fractionation was found to be (34)epsilon = -14.8 parts per thousand. The OCS sink reaction with O(P-3) cannot explain the large fractionation in S-34, over +73 parts per thousand, indicated by remote sensing data. In addition, (34)epsilon in OCS photolysis and OH oxidation are not larger than 10 parts per thousand, indicating that, on the basis of isotopic analysis, OCS is an acceptable source of background stratospheric sulfate aerosol.

Sulphuric acid is an important factor in aerosol nucleation and growth. It has been shown that ions enhance the formation of sulphuric acid aerosols, but the exact mechanism has remained undetermined. Furthermore some studies have found a deficiency in the sulphuric acid budget, suggesting a missing source. In this study the production of sulphuric acid from SO2 through a number of different pathways is investigated. The production methods are standard gas phase oxidation by OH radicals produced by ozone photolysis with UV light, liquid phase oxidation by ozone, and gas phase oxidation initiated by gamma rays. The distributions of stable sulphur isotopes in the products and substrate were measured using isotope ratio mass spectrometry. All methods produced sulphate enriched in S-34 and we find an enrichment factor (delta S-34) of 8.7 +/- 0.4 parts per thousand (1 standard deviation) for the UV-initiated OH reaction. Only UV light (Hg emission at 253.65 nm) produced a clear non-mass-dependent excess of S-33. The pattern of isotopic enrichment produced by gamma rays is similar, but not equal, to that produced by aqueous oxidation of SO2 by ozone. This, combined with the relative yields of the experiments, suggests a mechanism in which ionising radiation may lead to hydrated ion clusters that serve as nanoreactors for S(IV) to S(VI) conversion.