Absence Of Liquid Water Research Articles

Mold growth on pine and spruce wood: Dependence on moisture content, anatomical direction, and mold species

Better knowledge about the conditions for mold growth on wood could improve mold growth prediction models, prevent health risks, and increase the durability of wood without any additional biocidal treatment. Mold growth depends on the surrounding condition and the available nutrients. The most effective measure to prevent mold growth in wood-based houses is to keep the indoor relative humidity sufficiently low. We studied the dependence of mold growth on ambient relative humidity (75 - 95 % RH) at 23 °C with respect to the anatomical direction of wood and mold species. The samples were prepared from pine and spruce sapwood. The monitored parameters were the time of germination and the first macroscopic observation. Mold growth started at relative humidity higher than 75 %. Liquid water retarded mold germination. The germination time varied between 7 and 24 days in the absence of liquid water in the samples. The time from the first macroscopic observation ranged from 19 to 31 days under conditions without liquid water. Wetting the samples increased the time required to observe the first fungal growth at the microscopic and macroscopic levels. The use of variable humidity in the range of 75 – 95 % RH extended the time required for germination.

LithoSpace: An Idea for an Automated System for in situ Petrographic Thin Section Preparation on Mars and Other Extraterrestrial Rocky Bodies

Optical microscopy analyses using thin sections is one of the most standard techniques in geology. It permits identification of most rock-forming minerals and it is essential for micropaleontology since observation in transmitted light is the only way to observe individual, or colonies of, microfossils in their mineralogical and textural context. Thin sections are also used for other techniques such as Raman spectroscopy. In the framework of exploration of the Martian surface and of the search for potential relics of microbial life, the possibility to observe petrographic thin sections in situ would be revolutionary. Nevertheless, although optical microscopes can be readily designed for space exploration, thin section preparation is not easy to do in situ on extraterrestrial rocky bodies due to the generally harsh environmental conditions and to the difficulty to automate a protocol that normally requires several human interventions. The aim of the LithoSpace project, supported by the French Space Agency (CNES) since 2014, is to work on the development of an automated system permitting preparation of petrographic thin sections on extraterrestrial bodies, such as Mars, the Moon or asteroids. In this paper, we describe the approaches used to study rocks in situ during space missions and compare them to those used on Earth. Then, the relevance of making thin sections during space exploration is highlighted from the description of the data that could be collected from the analysis of these specific samples, using new instruments and instruments already sent to Mars. The standard preparation protocol is described as well as previously envisioned or existing in situ sample preparation systems. We then propose a protocol for automation of the preparation. Particular attention is paid to demonstrating the feasibility of making thin sections in the absence of liquid water and with energy consumption compatible with automated space probes. Tests are then carried out to control the quality of the prepared samples. On the basis of the demonstrated feasibility, an automated system is proposed as a conceptual all-in-one system. Finally, a “proof-of-concept” model developed with the help of students at different educational levels is presented.

Molecular Species Generated by Surface Dielectric Barrier Discharge Micro-plasma in Small Chambers Enclosing Atmospheric Air and Water Samples

In many applications of the atmospheric pressure plasmas, the plasma is generated in chambers that enclose samples to be treated. In the case of plasma treatments of water or water-containing materials, the humidity in gaseous medium rises during the treatment, and this affects considerably the plasma generation of reactive oxygen and nitrogen species (RONS). In this study, Fourier transform infrared absorption spectroscopy is used to investigate the kinetics of reactive species generated by surface dielectric barrier (SDBD) micro-plasma in a small volume of atmospheric air (0.5 L) enclosed in a discharge chamber. The investigations were made for dry air (in absence of liquid water) and for humid air in presence of liquid water. The SDBD plasma contributes to desorption of water from the inner wall of the discharge chamber and enhances evaporation of liquid water, which increases air humidity and decreases the generation rates of reactive species. Kinetics of RONS generated in small samples of liquid water in contact with discharge medium is investigated by ex situ UV absorption spectroscopy measurements of plasma treated water.

Thermal conductivity of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements

Abstract. Accurate description of snow and firn processes is necessary for estimating the fraction of glacier surface melt that contributes to runoff. Most processes in snow and firn are to a great extent controlled by the temperature therein and in the absence of liquid water, the temperature evolution is dominated by the conductive heat exchange. The latter is controlled by the effective thermal conductivity k. Here we reconstruct the effective thermal conductivity of firn at Lomonosovfonna, Svalbard, using an optimization routine minimizing the misfit between simulated and measured subsurface temperatures and densities. The optimized k* values in the range from 0.2 to 1.6 W (m K)−1 increase downwards and over time. The results are supported by uncertainty quantification experiments, according to which k* is most sensitive to systematic errors in empirical temperature values and their estimated depths, particularly in the lower part of the vertical profile. Compared to commonly used density-based parameterizations, our k values are consistently larger, suggesting a faster conductive heat exchange in firn.

Roles of Photon Scattering in Synchrotron X-ray Radiography of In Operando Visualizations of the Polymer Electrolyte Membrane Fuel Cell

Synchrotron X-ray radiography has been proven to be a powerful tool for visualizing and quantifying the in operando liquid water distributions in polymer electrolyte membrane (PEM) fuel cells. Water thickness, the accumulated water content at an image pixel, was calculated by normalizing the images collected to isolate the presence of liquid water. Images containing liquid water are called wet images, and are evaluated with respect to a reference image in the absence of liquid water, called the dry image. This normalization process is based on the Beer-Lambert law, and the attenuation coefficient of liquid water (at the applied photon energy level) is vital for this calculation. The attenuation coefficient for monoenergetic X-ray photons, provided by the National Institute of Standards and Technology (NIST), describes the probability that a photon will interact with the particles in a material as it travels a unit distance in the direction of the beam. Hence, the liquid water thickness calculation is highly dependent on the correct use of the attenuation coefficient. The incorrect use of a monoenergetic attenuation coefficient in synchrotron X-ray image analysis may lead to significant inaccuracies attributed to the neglect of scattering effects and higher harmonics contamination, which may be present at a synchrotron beamline. In our previous work (1), a calibration experiment was developed to experimentally obtain the water attenuation coefficient based from six known thicknesses of liquid water. The calibrated attenuation coefficient was 18.9% lower than the value for the monoenergetic photons at 20 keV. This deficit implied that at least one of the two prescribed phenomena (scattering and higher harmonics) contributed to the measured intensity in the obtained images. The purpose of this study is to determine the ratios of produced X-ray intensities that arise due to the scattering effect and higher harmonics, respectively. From this work, a correction method for calculating the water thickness can be proposed based on the scattering ratio. This correction method is vital for increasing the accuracy of water quantification. The calibration experiments were performed with a range of photon energy levels and filters at the Canadian Light Source. It was observed that the scattered signal increased as a function of water thickness, and this trend was more significant for lower experimental energy levels. The results suggested that the calibration experiment should be conducted with customized devices that contain liquid water with comparable quantities to that which one would find in the PEM fuel cell, in order to accurately simulate the in operando scattering effect. The existence of the higher harmonics was verified at the experimental energy level of 20 keV, and the water attenuation coefficient was experimentally measured to be 0.258 cm-1, which is in agreement with the value reported by NIST at 40 keV (0.268 cm-1). From the results obtained at 20 keV with the high-transmission filter, the ratio of higher harmonics was determined to be 0.9%–1.4% of the incident beam intensity. From this work, the authors urge that caution should be exercised when using selecting energy levels that could contain higher harmonic photons.

The role of water in the degradation of Pt3Co/C nanoparticles: An Identical Location Transmission Electron Microscopy study in polymer electrolyte environment

The degradation mechanisms of nanostructured Pt3Co/C electrocatalysts aged in dry electrochemical environment using a Nafion® 115 membrane as polymer electrolyte were characterized by Identical Location Transmission Electron Microscopy, in conditions that perfectly mimic real PEMFC operation. The structural, morphological and compositional changes of the Pt3Co/C nanoparticles occurring during an accelerated stress test were bridged to changes of their intrinsic kinetics toward the oxygen reduction reaction in Nafion® 115 electrolyte, thanks to an ultramicroelectrode with cavity loaded with the catalyst. The unique setup used herein further enabled to compare the Nafion® environment with conventional liquid electrolyte in which accelerated stress tests are usually performed. Although the Pt3Co/C nanoparticles are modified upon aging at Nafion® interface, the degradation processes are milder and different than those observed in liquid electrolyte, mostly following the absence of liquid water and the lack of ion mobility within the Nafion® membrane.

Study of individual reactions of the sour compression process for the purification of oxyfuel-derived CO 2

Following the feasibility study of sour compression process as a novel purification method of producing NO x -free, SO 2-free oxyfuel-derived CO 2 using actual fluegas, in this paper, we present the study of the individual reactions taking place in the process in a controlled environment. We have previously showed that an increase of NO/NO 2 concentration in the inlet stream is beneficial for SO 2 removal as NO 2 promotes SO 2 oxidation and the further removal as liquid acid. In this study we show that the reaction SO 2 + NO 2 → SO 3 + NO does not take place significantly in the absence of liquid water at a range of conditions relevant to the sour compression process. When liquid water is present, SO 2 is oxidised by NO 2 regenerating NO with the rate of conversion of SO 2 being dependent on the acid concentration in the liquid. The formation of small liquid droplets where very low levels of pH (≪0) can be reached is shown to be of great importance to the SO 2 + NO 2 conversion process.

Modeling an ordered nanostructured cathode catalyst layer for proton exchange membrane fuel cells

A 3D mathematical model of an ordered nanostructured cathode catalyst layer (CCL) has been developed for proton exchange membrane (PEM) fuel cells. In an ordered nanostructured CCL, carbon nanotubes (CNTs) are used as support material for Pt catalyst, upon which a thin layer of proton-conducting polymer (Nafion) is deposited, which are then aligned along the main transport direction (perpendicular to the membrane) of various species. The model considers all the relevant processes in different phases of an ordered nanostructured CCL. In addition, the effect of Knudsen diffusion is accounted in the model. The model can predict not only the performance of an ordered nanostructured CCL at various operating and design conditions but also can predict the distributions of various fields in different phases of an ordered nanostructured CCL. The predicted nanostructured CCL performance with estimated membrane overpotential is validated with measured data found in the literature, and a good agreement is obtained between the model prediction and measured result. Moreover, a parametric study is conducted to investigate the effect of key design parameters on the performance of an ordered nanostructured CCL. In the absence of liquid water, it is found that oxygen diffusion in the pore phase is not the limiting factor for the performance of an ordered nanostructured CCL, owing to its parallel gas pores and high porosity. However, the transport of dissolved oxygen through the Nafion phase has a significant effect on the performance of an ordered nanostructured CCL. Further, it is found that increasing the spacing between CNTs results in a considerable drop in the performance of an ordered nanostructured CCL at the base case conditions considered in the simulation.

Experimental measurement of portlandite carbonation kinetics with supercritical CO 2

A series of experiments was performed to observe and quantify the reactivity of portlandite with supercritical CO 2. The experiments were carried out in a batch reactor under different conditions: pressure of 160 bar, temperatures of 80, 120, and 200 °C, presence or absence of liquid water. Initial reaction rates are proposed, based on two independent techniques: measurements of the advancement of reaction by X-ray diffractometry (i.e. quantification of newly formed mineral assemblage), and monitoring of volume of CO 2 injected into the batch reactor to compensate for pressure drop during the experiment (CO 2 consumption, exsolution of secondary H 2O). The scanning electron microscopy observations show two different behaviours: in the presence of liquid water, the reaction leads to the complete carbonation of the portlandite into calcite. On the other hand, in the absence of a liquid phase, partial carbonation leads to the passivation of the portlandite surface by precipitation of a coating of tiny calcite crystals, and an incomplete weathering reaction of the portlandite.

Solar Variability and Climate Impact on Terrestrial Planets

Some possible factors of climate changes and of long term climate evolution are discussed with regard of the three terrestrial planets, Earth, Venus and Mars. Two positive feedback mechanisms involving liquid water, i.e., the albedo mechanism and the greenhouse effect of water vapour, are described. These feedback mechanisms respond to small external forcings, such as resulting from solar or astronomical constants variability, which might thus result in large influences on climatic changes on Earth. On Venus, reactions of the atmosphere with surface minerals play an important role in the climate system, but the involved time scales are much larger. On Mars, climate is changing through variations of the polar axis inclination over time scales of ∼105–106 years. Growing evidence also exists that a major climatic change happened on Mars some 3.5 to 3.8 Gigayears ago, leading to the disappearance of liquid water on the planet surface by eliminating most of the CO2 atmosphere greenhouse power. This change might be due to a large surge of the solar wind, or to atmospheric erosion by large bodies impacts. Indeed, except for their thermospheric temperature response, there is currently little evidence for an effect of long-term solar variability on the climate of Venus and Mars. This fact is possibly due to the absence of liquid water on these terrestrial planets.

Stability of interstellar fullerenes under high-dose γ-irradiation: new data

The detection of fullerenes in carbonaceous chondrites and in the geological strata of the Cretaceous–Tertiary boundary layer, associated with the Yucatan bolide impact, can be considered as an indirect evidence of fullerene formation in circumstellar envelopes of mass-losing carbon-rich stars. The large carbon clusters are very stable compounds with the respect to various physical and chemical factors. Nevertheless only scarce data on their behavior under high-dose γ-irradiation are available. This aspect is of crucial importance for the chemistry of interstellar fullerenes, since the existence of the large spherical carbon clusters must finally depend on competition between the rates of their formation and radiation decomposition. In continuation of our studies of the capability of solid C 60 fullerene to withstand prolonged γ-irradiation, in the present work we report on a long duration experiment, lasted for ca. 8 months. We found that the degree of C 60 decomposition, both in the presence and absence of liquid water, was less than 15%, demonstrating its extreme stability. A similar fullerene stability can be expected in different space environments, where the large carbon clusters are formed, incorporated into interstellar dust particles and subsequently into comets, and travel through the Universe.

Influence of Catalyst Layer Structure on the Current Distribution of PEMFCs

a modified subcell approach was adopted to evaluate the current density distributions of proton exchange membrane fuel cells (pemfcs) with different electrodes. conventional hydrophobic electrodes showed better performance under flooding conditions compared to hydrophilic electrodes. the thin-film hydrophilic electrode performed better in the absence of liquid water, but it was more readily flooded. a composite catalyst layer was designed with 2/3 of the area from the inlet prepared hydrophilic and the remaining 1/3 area hydrophobic. the composite catalyst layer with commercial scale dimension showed notable enhanced performance in the concentration polarization region. (c) 2004 the electrochemical society.

Stability of interstellar fullerenes under high-dose γ-irradiation

It is generally assumed that the large spherical carbon clusters can be generated within circumstellar envelopes of mass-losing carbon-rich stars. The detection of fullerenes in carbonaceous chondrites, in the geological strata of the Cretaceous–Tertiary and the Permian–Triassic boundary layers, associated with bolide impacts, can be considered as an indirect evidence of their formation in circumstellar envelopes. On the other hand, a question arises on the fate of fullerenes in harsh radiation environments: namely, in close proximity to the stars where they have been produced (the gas phase), and in the solid phase after their incorporation into the interstellar grains. The existence of the large spherical carbon clusters must finally depend on competition between the rates of their formation and radiation decomposition. In the present work we estimated the capability of C 60 fullerene to withstand prolonged γ-irradiation, under the doses exceeding 6 MGy (1 Gy=1 J kg −1), in the presence and absence of liquid water. The results of high-performance liquid chromatographic and infrared spectroscopic measurements of the irradiated products suggest general pathways of C 60 radiolysis in the aqueous phase to be polymerization (most likely cross-linking), breaking the carbon backbone, C–H group formation, and incorporation of oxygen atoms as carbonyl and OH groups. In the absence of water, attachment of other radicals generated in the environment is possible, along with the polymerization. As a whole, crystalline C 60 fullerene exhibited an extremely high stability. A similar behavior can be expected in different space environments, where the large carbon clusters are formed, incorporated into interstellar dust particles and subsequently into comets, and travel through the Universe.

Spurious aerosol measurements when sampling from aircraft in the vicinity of clouds

Extensive airborne measurements of aerosol particles in a pristine marine region were made during the first Aerosol Characterization Experiment (ACE 1) from November 15 to December 14, 1995. During this study, high concentrations of condensation nuclei (CN) were frequently observed both near and within clouds. Near clouds, in the absence of liquid water, Clarke et al. [1998] have reported that high CN levels were from new particle formation by homogeneous nucleation. Here we show, however, that within clouds, elevated CN concentrations were not authentic, but instead a sampling artifact, likely related to fragmentation of cloud drops impacting the aerosol inlet. By themselves, these fragments were often indistinguishable from ambient particles. Spurious CN from fragmenting droplets were observed at temperatures down to roughly −20°C and spanned a broad size range, with diameters down to 3 nm. Comparison of two different sized isokinetic aerosol inlets showed that inlets with smaller openings produce higher droplet fragment concentrations. The mechanism for producing these particles is not completely understood. Although fragmentation appeared to be the primary mechanism, for one instrument, an additional spurious source, correlated with liquid water, was observed when ambient temperatures were below −5°C. These findings show that care must be taken when interpreting airborne aerosol measurements in regions of liquid water. This is particularly pertinent to studies of new particle formation by homogeneous nucleation in the vicinity of clouds.

An exobiological view of Titan and the Cassini-Huygens mission

The largest satellite of Saturn, Titan, is the only one in the solar system having a dense atmosphere. In many aspects it is similar to the Earth. Moreover, organic chemistry on Titan and prebiotic chemistry on Earth involve the same N-containing organic molecules: nitriles, including acetylenic nitriles and dinitriles, and their oligomers. Thus, in spite of much lower temperatures and the absence of liquid water, because of its environment very rich in organics, and the many couplings involved in the various parts of its “geofluid”, Titan is a reference laboratory for studying prebiotic chemistry on a planetary scale. In the frame of the NASA-ESA Cassini-Huygens mission, which includes an orbiter (Cassini) around Saturn and a probe (Huygens) in Titan's atmosphere, organic chemistry in Titan's “geofluid” will be studied in great detail. In situ measurements, in particular from Huygens GC-MS and ACP instruments, will provide detailed analysis of the organics present in the air, aerosols, and surface. The mission will be launched in october 1997, for an arrival in the Saturn System in 2004. Thus, at horizon 2000, we can expect many information of crucial importance for the field of exobiology.

Experiments on the role of water in petroleum formation

Pyrolysis experiments were conducted on immature petroleum source rocks under various conditions to evaluate the role of water in petroleum formation. At temperatures less than 330°C for 72 h, the thermal decomposition of kerogen to bitumen was not significantly affected by the presence or absence of liquid water in contact with heated gravel-sized source rock. However, at 330 and 350°C for 72 h, the thermal decomposition of generated bitumen was significantly affected by the presence or absence of liquid water. Carbon-carbon bond cross linking resulting in the formation of an insoluble bitumen (i.e., pyrobitumen) is the dominant reaction pathway in the absence of liquid water. Conversely, thermal cracking of carbon-carbon bonds resulting in the generation of saturate-enriched oil, which is similar to natural crude oils, is the dominant reaction pathway in the presence of liquid water. This difference in reaction pathways is explained by the availability of an exogenous source of hydrogen, which reduces the rate of thermal decomposition, promotes thermal cracking, and inhibits carbon-carbon bond cross linking. The distribution of generated n-alkanes is characteristic of a free radical mechanism, with a broad carbon-number distribution (i.e., C 5 to C 35) and only minor branched alkanes from known biological precursors (i.e., pristane and phytane). The generation of excess oxygen in the form of CO 2 in hydrous experiments and the high degree of hydrocarbon deuteration in a D 2O experiment indicate that water dissolved in the bitumen is an exogenous source of hydrogen. The lack of an effect on product composition and yield with an increase in H + activity by five orders of magnitude in a hydrous experiment indicates that an ionic mechanism for water interactions with thermally decomposing bitumen is not likely. Several mechanistically simple and thermodynamically favorable reactions that are consistent with the available experimental data are envisaged for the generation of exogenous hydrogen and excess oxygen as CO 2. One reaction series involves water oxidizing existing carbonyl groups to form hydrogen and car☐yl groups, with the latter forming CO 2 by decar☐ylation with increasing thermal stress. Another reaction series involves either hydrogen or oxygen in dissolved water molecules directly interacting with unpaired electrons to form a hydrogen-terminated free-radical site or an oxygenated functional group, respectively. The latter is expected to be susceptible to oxidation by other dissolved water molecules to generate additional hydrogen and CO 2. In addition to water acting as an exogenous source of hydrogen, it is also essential to the generation of an expelled saturate-enriched oil that is similar to natural crude oil. This role of water is demonstrated by the lack of an expelled oil in an experiment where a liquid Ga In alloy is substituted for liquid water. Experiments conducted with high salinity water and high water/rock ratios indicate that selective aqueous solubility of hydrocarbons is not responsible for the expelled oil generated in hydrous pyrolysis experiments. Similarly, a hydrous pyrolysis experiment conducted with isolated kerogen indicates that expelled oil in hydrous pyrolysis is not the result of preferential sorption of polar organic components by the mineral matrix of a source rock. It is envisaged that dissolved water in the bitumen network of a source rock causes an immiscible saturate-enriched oil to become immiscible with the thermally decomposing polar-enriched bitumen. The overall geochemical implication of these results is that it is essential to consider the role of water in experimental studies designed to understand natural rates of petroleum generation, expulsion mechanisms of primary migration, thermal stability of crude oil, reaction kinetics of biomarker transformations, and thermal maturity indicators in sedimentary basins.

Prebiotic-Related Chemistry in the Present Outer Solar System

AbstractThere are numerous places in the outer solar system where the formation of the starting ingredients which are involved in the early terrestrial prebiotic chemistry is currently going on. Organic chemistry is largely present in the outer planets, particularly in Titan. Titan has a dense atmosphere, mainly composed of N2and CH4and very rich in organic compounds, both in gas and aerosol phases. Because of the low temperature of Titan’s environment, liquid water is currently absent from the satellite and compounds of low stability at the (Earth) laboratory temperature, and very reactive, are still or may be present. However, Titan study should provide information on prebiotic chemistry – at least prebiotic chemistry in absence of liquid water. This quasi-planet thus appears as a natural laboratory enabling to study prebiotic evolution toward complex organic systems in a planetary environment over a long time scale. A detailed study of such a natural prebiotic laboratory is precisely one of the main objectives of the Cassini-Huygens mission. With the sending of the Cassini orbiter around Saturn and the Huygens probe in the atmosphere of Titan, this mission, due to be launched in October 1997, for a Saturn arrival in 2004, will offer a unique opportunity to study in detail extra-terrestrial prebiotic processes, together with important implications in the field of bioastronomy and the origins of life.

In-Plane Diffusivity of Moisture in Paper

ABSTRACT Any nonuniformity in local moisture content of paper which develops during drying because of locally nonuniform drying rates provides a driving force for in-plane diffusion of moisture, which in turn acts to reduce this moisture nonuniformity. As no data have appeared for the in-plane diffusivity of moisture during desorption from paper over the range of conditions existing during papermachine drying, an investigation was undertaken to obtain this information. Moisture diffusivity was determined to he a very strong function of the extent and state of water in the sheet, increasing exponentially with paper moisture content. The presence or absence of liquid water at the sheet boundary would effect moisture difiusivity when there is water in the pores but the direction of moisture transport in paper was found to be of overriding importance. In-plane moisture diffusivity is very much greater than that in the thickness direction, indicating that the non-isotropic nature of paper structure is a key factor. A microscale view of the mechanism of moisture transport in the thickness and in-plane directions was developed, consistent with the enormous difference in effect of moisture content on diffusivity in the two directions.

Millisecond Fourier-transform infrared difference spectra of bacteriorhodopsin's M412 photoproduct.

We have obtained room-temperature transient infrared difference spectra of the M412 photoproduct of bacteriorhodopsin (bR) by using a "rapid-sweep" Fourier-transform infrared (FT-IR) technique that permits the collection of an entire spectrum (extending from 1000 to 2000 cm-1 with 8-cm-1 resolution) in 5 ms. These spectra exhibit less than 10(-4) absorbance unit of noise, even utilizing wet samples containing approximately 10 pmol of bR in the measuring beam. The bR----M transient difference spectrum is similar to FT-IR difference spectra previously obtained under conditions where M decay was blocked (low temperature or low humidity). In particular, the transient spectrum exhibits a set of vibrational difference bands that were previously attributed to protonation changes of several tyrosine residues on the basis of isotopic derivative spectra of M at low temperature. Our rapid-sweep FT-IR spectra demonstrate that these tyrosine/tyrosinate bands are also present under more physiological conditions. Despite the overall similarity to the low-temperature and low-humidity spectra, the room-temperature bR----M transient difference spectrum shows significant additional features in the amide I and amide II regions. These features' presence suggests that a small alteration of the protein backbone accompanies M formation under physiological conditions and that this conformational change is inhibited in the absence of liquid water.

Oxygen-18 study of nonaqueous-phase oxidation of sulfur dioxide

In a study of the mechanisms of atmospheric sulfate formation, oxygen isotope ratios were measured in sulfates and in the SO 2 and water vapors from which they were formed, in the absence of liquid water. In a 3-ℓ glass chamber, SO 2 and water vapor of various 18O contents were isotopically equilibrated, and then air oxidation of the SO 2 to sulfate was performed by four different methods: high-voltage discharges, NO 2 addition, gamma irradiation and adsorption on activated charcoal. Isotopic equilibration between SO 2 and water vapor proceeded rapidly, resulting in a strong dependence of the δ 18O of the sulfate on that of the water vapor. Oxidation of SO 2 on dry charcoal occurred through the apparent formation of 9-oxygen, 2-sulfur, chemisorbed molecules which decomposed to sulfate in leach water. The δ 18 O SO 2− 4 vs δ 18 O H 2 O relationships observed for these four nonaqueous-phase oxidations of SO 2 to sulfate, together with those in three previously reported aqueous-phase oxidations ( Fe 3+-catalyzed air oxidation, charcoal-catalyzed air oxidation and H 2 O 2 oxidation), were compared to sulfate in rain and snow collected at Argonne, IL. The δ 18 O of sulfate in precipitation water was significantly higher than could be accounted for by any of the several oxidation reactions that were investigated as possible pathways in the formation of secondary sulfates in the atmosphere, either singly or in combination.