Vapor Composition Research Articles

Causes for overestimation of the moisture recycling in an alpine meadow ecosystem of the Shule River Basin, Tibetan Plateau, China

Terrestrial moisture recycling is an essential hydrological component and a significant source of the atmosphere’s humidity budget in arid and semi-arid inland regions. Investigations on moisture recycling using the stable hydrogen and oxygen isotopes is currently a focal point in hydrologic research. However, the direct quantification of recycling ratio based on isotopic composition of evapotranspiration vapor is lacking. So, this causes challenges to compare studies, based in the same region and time period but with different methodologies. In this study, we measured the isotopic compositions of evapotranspiration vapor (δ18OET/δDET) from June to September 2018 in an alpine meadow ecosystem at the Shule River Basin by combining the Keeling plot model and in-situ chamber measurement. Using this data, the moisture recycled rate (mrr) was assessed based on the two-component (Model A) and three-component isotopic mixing models (Model B), respectively. Based on Model A and δ18OET, the analysis revealed that the mean recycled rate for the entire observation period was 35 %, while it was 26 % during the westerly period (the months dominated by the north branch of prevailing westerlies) and 44 % during the monsoon period (when subtropical moisture from the Indian monsoon penetrated the region). The recycled rate based on Model A and δDET was slightly larger with a mean value of 41 % during the entire observation period. The recycled rate based on Model B was also significantly higher in comparison with Model A, while the causes for this difference could be the assumption of substituting xylem water for transpiration vapor and the plant water source δD offset. The contribution of recycled moisture was notable lower for heavy rainfall comparing with light rainfall. Our findings provided a new perspective for the investigations of alpine meadow ecosystem hydrological processes.

Is There an Adduct of Pyridine N-Oxide and Boron Trifluoride in the Gaseous State? Gas Electron Diffraction vs Mass Spectrometry.

A study of saturated vapor over the pyridine N-oxide-boron trifluoride (PyO-BF3) adduct was carried out at T = 448(5) K by a synchronous gas electron diffraction/mass spectrometry (GED/MS) experiment. Due to the absence of ions in the mass spectrum, indicating the presence of a structure with an O-B dative bond, several models of vapor composition were tested by the GED method. It was found that the dominant molecular form (up to 100%) in vapor is the PyO-BF3 adduct. Using the DFT/M06-2X/aug-cc-pVTZ method, geometric optimization of the molecular ion [PyO-BF3]+ was carried out, which showed its intrinsic instability and dissociation into a [PyO]+ cation and a BF3 molecule. This study certainly demonstrates the significant advantage of the GED method to determine the qualitative and quantitative gas-phase composition of dative-bonded adducts and other noncovalent complexes as well, whereas the interpretation of mass spectra may be ambiguous due to the possible intrinsic instability of ions containing a dative bond. The nature of the O-B bond is discussed in terms of the natural bond orbitals (NBOs) and the quantum theory of atoms in molecules (QTAIM). A comparison of structural and energetic parameters for PyO-BF3 and the previously studied BF3 adducts allows the theoretical comprehension of the nature of the O-B bond to be extended and to explain the different thermal stabilities of these compounds.

Intra-annual variations in isotopic composition of atmospheric water vapour in a semi-arid monsoon region: observations and inferences

The isotopic composition of atmospheric water vapour dynamically changes due to the complex interplay between the moisture-contributing sources (precipitation, evaporating soil moisture, transpiration, evaporating water bodies, etc.), operating ecohydrological processes, and the climatic conditions. In the present study, the isotopic composition of different sources of water was sampled; air moisture (n = 47) twice a month for the period December, 2021 to January, 2023; transpiration samples (n = 76); evaporation and rain samples (n = 12 each). The samples were analyzed using the mass spectrometry to investigate the dynamic nature of the isotopic composition of the atmospheric vapour and the factors influencing it. The research findings showed that the isotopic composition of atmospheric moisture rapidly depleted after the onset of the monsoon, indicating the replacement of pre-monsoon local vapour by monsoon moisture of depleted isotopic composition. The process of evaporation from the soil surface during the post-monsoon period was found to progress parallel to other soil hydrological processes, such as capillary action and diffusion-driven downward flux of enriched water molecules. This resulted in the broadening of an isotopically enriched layer of soil moisture in the vadose zone with time, and accordingly, there was transpiration of this enriched soil moisture from the deeper layers of soils with time by plants/trees. Evaporation of soil water and the transpiration of plants and trees of enriched water vapour gradually altered the isotopic composition of the atmospheric water vapour composition from the depleted isotopic composition of the monsoon period to an enriched isotopic composition. The transpiration of enriched water vapour from deep-rooted trees indicated more prolonged arid climate conditions. The findings of the study are useful in understanding the regional hydrological and hydroclimatic processes which can be implemented in agro-climatic studies and water resource management.

Heavy Water Microdroplet Surface Enriches the Lighter Isotopologue Impurities.

Water microdroplets promote unusual chemical reactions at the air-water interface. However, the interfacial structure of water microdroplets and its potential influence on chemical processes are still enigmatic. Here, we present evidence of in-droplet fractionation of water isotopologues. Employing a sonic spray, we atomized the heavy water (D2O, 99.9 atom % D) solution of three classes of organic compounds (basic, acidic, and neutral). The analytes were predominantly desorbed from the resulting droplet surface in protonated form rather than deuterated form, as detected by mass spectrometry. This result remained unaltered upon adding formic acid-d2 (DCOOD) to the droplet. Monitoring Dakin oxidation of benzaldehyde at the surface of binary microdroplets composed of 1:1 (v/v) D2O/H218O revealed the preferred formation of phenolate-16O over phenolate-18O. Atmospheric pressure chemical ionization mass spectrometric analysis of the vapor composition in the sprayed aerosol revealed the preferential evaporation of lighter water isotopologue impurities from the surface of heavy water microdroplets. These results indicate the enrichment of lighter water isotopologue impurities (HOD/H2O) on the surface of heavy water microdroplets, implying possible future developments for water isotopologue fractionation using microdroplets.

Congo Basin Water Balance and Terrestrial Fluxes Inferred From Satellite Observations of the Isotopic Composition of Water Vapor

AbstractLarge spatio‐temporal gradients in the Congo basin vegetation and rainfall are observed. However, its water‐balance (evapotranspiration minus precipitation, or ET − P) is typically measured at basin‐scales, limited primarily by river‐discharge data, spatial resolution of terrestrial water storage measurements, and poorly constrained ET. We use observations of the isotopic composition of water vapor to quantify the spatio‐temporal variability of net surface water fluxes across the Congo Basin between 2003 and 2018. These data are calibrated at basin scale using satellite gravity and total Congo river discharge measurements and then used to estimate time‐varying ET − P over four quadrants representing the Congo Basin, providing first estimates of this kind for the region. We find that the multi‐year record, seasonality, and interannual variability of ET − P from both the isotopes and the gravity/river discharge based estimates are consistent. Additionally, we use precipitation and gravity‐based estimates with our water vapor isotope‐based ET − P to calculate time and space averaged ET and net river discharge within the Congo Basin. These quadrant‐scale moisture flux estimates indicate (a) substantial recycling of moisture in the Congo Basin (temporally and spatially averaged ET/P > 70%), consistent with models and visible light‐based ET estimates, and (b) net river outflow is largest in the Western Congo where there are more rivers and higher flow rates. Our results confirm the importance of ET in modulating the Congo water cycle relative to other water sources.

Effect of membrane properties on the odor emanating from training aids for explosive-detecting canines.

Canines are widely used for real-time detection of explosives and have proven to be on par with instrumental methods. Canines are thought to rely largely upon detection of volatile chemical constituents of the explosives, though not necessarily the explosive itself. Hence, it is crucial to understand the odor available to them as generated by training aids. Previous studies have established that the Training Aid Delivery Device (TADD) developed by SciK9 is a reliable training aid that reduces cross-contamination and doubles as a storage device. A TADD comprises a standardized container, a synthetic membrane, a membrane holder, and a lid. In the work presented, activated charcoal strips were placed above and below the TADD membrane to determine the relative amounts of volatiles emitted by dynamite (i.e., ethylene glycol dinitrate (EGDN) and trinitroglycerin (NG)). The strips were eluted and the extracts tested using gas chromatography-mass spectrometry in negative ion chemical ionization mode. A series of t-tests at 95% confidence level were performed to determine any differences in vapor composition above and below the membranes. Nine synthetic membranes and six glass fiber membranes were tested in this study. It was expected that the relative concentration of volatiles would remain the same on both sides of the membrane; however, selective removal of nitroglycerin by some membranes was observed. Synthetic membranes with larger pore sizes showed no alteration in the vapor composition. Both synthetic and glass fiber membranes did not show a significant change in relative concentration of the other volatile compound in dynamite, i.e., EGDN. Out of all the membranes tested, three synthetic membranes and four glass fiber membranes showed selective alteration in odor availability of nitroglycerin in dynamite. For training purposes, membranes that do not alter the vapor composition should be used in the training aid.

Comparison of the H2O, HDO and δD stratospheric climatologies between the MIPAS-ESA V8, MIPAS-IMK V5 and ACE-FTS V4.1/4.2 satellite datasets

Abstract. Variations in the isotopologic composition of water vapour are fundamental for understanding the relative importance of different mechanisms of water vapour transport from the tropical upper troposphere to the lower stratosphere. Previous comparisons obtained from observations of H2O and HDO by satellite instruments showed discrepancies. In this work, newer versions of H2O and HDO retrievals from Envisat/MIPAS and SCISAT/ACE-FTS are compared. Specifically, MIPAS-IMK V5, MIPAS-ESA V8 and ACE-FTS V4.1/4.2 for the common period from February 2004 to April 2012 are compared for the first time through a profile-to-profile approach and comparison based on climatological structures. The comparison is essential for the scientific community to assess the quality of new satellite data products, a necessary procedure to validate further scientific work. Averaged stratospheric H2O profiles reveal general good agreement between 16 and 30 km. Biases derived from the profile-to-profile comparison are around zero between 16 and 30 km for MIPAS-IMK and ACE-FTS comparison. For HDO and δD, low biases are found in the MIPAS-ESA and ACE-FTS comparison in the same range of altitudes, even if associated with a larger de-biased standard deviation. The zonally averaged cross sections of H2O and HDO exhibit the expected distribution that has been established in previous studies. For δD the tropical depletion in MIPAS-ESA occurs at the top of the dynamical tropopause, but this minimum is found at higher altitudes in the ACE-FTS and MIPAS-IMK dataset. The tape recorder signal is present in H2O and HDO for the three databases with slight quantitative differences. The δD annual variation for ACE-FTS data and MIPAS-ESA data is weaker compared to the MIPAS-IMK dataset, which shows a coherent tape recorder signal clearly detectable up to at least 30 km. The observed differences in the climatological δD composites between databases could lead to different interpretations regarding the water vapour transport processes toward the stratosphere. Therefore, it is important to further improve the quality of level 2 products.

Vapor Composition and Thermodynamic Characteristics of Gaseous Molecules of Alkaline Earth Metal Tungstates

Vapor Composition and Thermodynamic Characteristics of Gaseous Molecules of Alkaline Earth Metal Tungstates

Improvements in the Quantification of End-Member Vapor Compositions in Fluid Inclusion Boiling Assemblages and Implications for Metal Transport by Low-Density Fluids

Abstract Under conditions typically found in the Earth’s crust, there is a large pressure-temperature-composition range in the H2O-NaCl system where fluids may separate into a low-salinity vapor end member and a high-salinity liquid end member. However, heterogeneous trapping is common during the formation of fluid inclusions in an immiscible fluid system, violating the fundamental assumption of homogeneous entrapment for fluid inclusion microthermometry. This has profound consequences on the composition of these fluid phases and consequently on the formation of ore deposits from hydrothermal systems. At the same time, minor mixture of the high-salinity liquid phase with the low-salinity vapor phase cannot be distinguished from the end-member vapor-rich fluid inclusions by their bubble sizes. Precise determination of the salinities of vapor-rich fluid inclusions using microthermometry is deterred by the very small proportion of the liquid phase and the limitation of the analytical precision. All this will lead to erroneous compositional data from fluid inclusion analysis. We have quantitively calculated the variations of fluid inclusion properties caused by heterogeneous entrapment during phase separation in the H2O-NaCl system and showed that the salinity, and thereby the element contents and element/Na ratios of the vapor-rich fluid inclusions, is significantly changed in heterogeneously trapped fluid inclusions. The addition of 1 vol % of the high-salinity end member to the low-salinity end member results in a salinity change from 0.99 to 4.4 wt % NaCl equiv at the phase separation condition of 800 bar and 750°C. This will have a significant impact when it comes to determining the concentration of elements transported as chlorine complexes and typically leads to an overestimation of the mass transport capability by the vapor phase. Therefore, every effort should be taken during microthermometry to find and measure the least affected vapor-rich fluid inclusions. Our numerical calculations and synthetic fluid inclusions reveal that there is a linear relationship between the salinity and element contents for fluid inclusions at different extents of heterogeneous entrapment. Therefore, linear correction to the measured lowest vapor salinity can obtain a good approximation of the element contents in the end-member vapor phase.

Partitioning evapotranspiration of Camellia oleifera during the growing season based on the Penman-Monteith model combined with the micro-lysimeter and stable isotope methods

Frequent seasonal droughts impact on crop growth and yield in the hilly areas of southern China. A good knowledge of its evapotranspiration partitioning of the main economic oil crop Camellia Oleifera is particularly important to increase water productivity and improve water resource management. The isotope-based method was applied to partition ET in the hilly Camellia Oleifera Forest of southern China. The isotopic composition of evapotranspiration vapor (δET), transpiration vapor (δT) and evaporation vapor (δE) were calculated by the Keeling plot method, the Craig-Gordon model (C-G model), and isotopic steady-state assumptions, respectively. The conventional Penman-Monteith model and the micro-lysimeter method (PM-L) were used to compare and assess the ET partitioning results (Ft). It showed that the Ft values calculated by the two methods were in good agreement. The isotopic composition of soil water at the evaporating front (δS) ahead and after DOY151 was sampled at 5 and 10 cm depth, respectively, where the correlation coefficients (R2) of the Ft values calculated by δ18O and δ2H were 0.84 and 0.66. Ft Calculated by δ18O was more accurate than δ2H because of the higher correlation coefficient of δ18O in the keeling plot regression and in the linear fit with PM-L. The isotopic composition of soil evaporation vapor（δE）calculated by dynamic εk (kinetic fractionation effects) values can be more accurate to quantify the ET partitioning results (with the R2 of 0.90). The mean values of Ft were 0.79 and 0.82 by the PM-L method and the isotope-based method respectively over the whole growing season, indicating the isotope method is robust in calculating ET partitioning for Camellia oleifera in the region. We also found that the seasonal variation of Ft is mainly controlled by temperature (T), soil water content (SWC), and leaf area index (LAI), all of which can be effectively expressed as power functions. The results provide potential assistance for water management in Camellia oleifera woodlands.

Constraining the global composition of D/H and 18O/16O in Martian water using SOFIA/EXES

ABSTRACT Isotopic ratios in water vapour carry important information about the water reservoir on Mars. Localized variations in these ratios can inform us about the water cycle and surface–atmosphere exchanges. On the other hand, the global isotopic composition of the atmosphere carries the imprints of the long-term fractionation, providing crucial information about the early water reservoir and its evolution throughout history. Here, we report the analysis of measurements of the D/H and 18O/16O isotopic ratios in water vapour in different seasons (LS = 15○, 127○, 272○, and 305○) made with the Echelon-Cross-Echelle Spectrograph (EXES) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). These measurements, free of telluric absorption, provide a unique tool for constraining the global isotopic composition of Martian water vapour. We find the maximum planetary D/H ratio in our observations during the northern summer (D/H = 5.2 ± 0.2 with respect to the Vienna Standard Mean Ocean Water, VSMOW) and to exhibit relatively small variations throughout the year (D/H = 5.0 ± 0.2 and 4.3 ± 0.4 VSMOW during the northern winter and spring, respectively), which are to first order consistent though noticeably larger than the expectations from condensation-induced fractionation. Our measurements reveal the annually averaged isotopic composition of water vapour to be consistent with D/H = 5.0 ± 0.2 and 18O/16O = 1.09 ± 0.08 VSMOW. In addition, based on a comparison between the SOFIA/EXES measurements and the predictions from a Global Climate Model, we estimate the D/H in the northern polar ice cap to be $\sim\!{5}~{{\ \rm per\ cent}}$ larger than that in the atmospheric reservoir (D/Hice = 5.3 ± 0.3 VSMOW).

Effect of Energy-driven Molecular Precursor Decomposition on the Crystal Orientation of Antimony Selenide Film and Solar Cell Efficiency.

Antimony selenide (Sb2Se3) consists of 1D (Sb4Se6)n ribbons, along which the carriers exhibit high transport efficiency. By adjusting the deposition parameters of vacuum-deposited methods, such as evaporation temperature, chamber pressure, and vapor concentration, it is possible to grow the (Sb4Se6)n ribbons vertically or highly inclined towards the substrate, resulting in films with [hk1] orientation. However, the specific mechanisms by which these deposition parameters affect the orientation of thin films require a deeper understanding. Herein, a molecular beam epitaxy technique is developed for the preparation of highly [hk1]-oriented Sb2Se3 films, and the effect of evaporation parameters on the film orientation is investigated. It is found that the evaporation temperature can affect the decomposition degree of Sb2Se3, which in turn determines the vapor composition and film orientation. Additionally, the decomposition of Sb2Se3 related to evaporation temperature leads to significant changes in the elemental composition of the film, thereby passivating deep-level defects under Se-rich conditions. Consequently, the Sb2Se3 films with highly [hk1] orientation achieve a power conversion efficiency of 8.42% for the solar cells. This study provides new insights into the control of orientation in antimony-based chalcogenide films and points out new directions for improving the photovoltaic performance of solar cells.

Spring tropical cyclones modulate near-surface isotopic compositions of atmospheric water vapour in Kathmandu, Nepal

Abstract. While westerlies are recognized as a significant moisture transport in Nepal during the pre-monsoon season, precipitation is also attributed to moisture from cyclones originating in the Bay of Bengal (BoB) or the Arabian Sea (AS). Tropical cyclones exhibit negative isotopic values in both precipitation and atmospheric water vapour; however, the factors influencing isotopic fractionation during tropical cyclones remain poorly understood. We present the results of continuous measurements of the isotopic composition of atmospheric water vapour (δ18Ov, δDv, and d-excessv) in Kathmandu from 7 May to 7 June 2021 during two pre-monsoon cyclones: cyclone Tauktae, formed over the Arabian Sea, and cyclone Yaas, formed over the Bay of Bengal. Our study reveals that tropical cyclones originating from the BoB and the AS during the pre-monsoon season modulate isotopic signals of near-surface atmospheric water vapour in Nepal. Comparing conditions before and after, we observed a significant depletion of δ18Ov and δDv during both cyclones, attributed to changes in moisture sources (local vs. marine). Convective activity plays a pivotal role in the variability of δ18Ov and δDv during both cyclones, confirmed by the spatial variations of outgoing longwave radiation (OLR) and regional precipitation during both cyclones. We also found a significant negative correlation between δ18Ov and/or δDv and rainfall amount along the trajectories during cyclone Tauktae, probably resulting from integrated upstream processes linked to the earlier Rayleigh distillation of water vapour via rainfall rather than local rainfall. The decrease in δ18Ov and/or δDv during cyclone Yaas is associated with the intensified convection and moisture convergence at the measurement site, while the lower cloud top temperatures (CTTs) and lower cloud top pressure (CTP) during intense convection contribute to higher d-excessv values during the final stage of cyclone Yaas. This characteristic is missing during cyclone Tauktae. Our results shed light on key processes governing the isotopic composition of atmospheric water vapour in Kathmandu with implications for the monsoon moisture transport and paleoclimate reconstructions of tropical cyclone activity.

Is the Isotopic Composition of Precipitation a Robust Indicator for Reconstructions of Past Tropical Cyclones Frequency? A Case Study on Réunion Island From Rain and Water Vapor Isotopic Observations

AbstractBased on a 6‐year long record (2014–2020) of the isotopic composition of rain (δ18Op) at Réunion Island (55°E, 22°S), in the South‐West Indian Ocean, this study shows that the annual isotopic composition of precipitation in this region is strongly controlled by the number of cyclones, the number of best‐track days, and the proportion of cyclonic rain during the year. Our results support the use of δ18Op in annual‐resolved tropical climate archives as a reliable proxy of past cyclone frequency. The influence of the proportion of cyclonic rain on the annual isotopic composition arises from the systematically more depleted precipitation and water vapor during cyclonic events than during less organized convective systems. The analysis of the daily to hourly isotopic composition of water vapor (δ18Ov) during low‐pressure systems and the reproduction of daily δ18Ov observations by AGCMs with a global medium to coarse resolution (LMDZ‐iso and ECHAM6‐wiso) suggest that during cyclonic periods the stronger depletion mainly arises from both enhanced large‐scale precipitation and water vapor‐rain interactions under humid conditions.

Pyrolysis kinetics behavior and pyrolysate compositions analysis of agriculture waste toward the production of sustainable renewable fuel and chemicals

AbstractThis work deals with the characterization of feed, kinetic, and compositional study of sugarcane baggage (SCB) using a thermogravimetric analyzer (TGA), Py‐GC‐MS, and X‐ray fluorescence (XRF) analyzer. XRF analyzer was used to determine the mineral of ash content, and Py‐GC‐MS was employed to determine the hot vapor composition produced during fast pyrolysis. Cots‐Redfrem (CR) methods and master plots were utilized to determine the kinetic parameters. Studies on the physicochemical properties of SCB have demonstrated its potential for use as a bioenergy feedstock. The average activation energy was found to be 25.44 kJ mol−1 at (n = 1) and 31.21 kJ mol−1 at n ≠ 1 using the CR model. The master plot study suggested that pyrolysis occurred with various mechanisms, while kinetic results of SCB demonstrated that activation energy varied with conversion value. XRF examination revealed significant mineral materials that aided in the pyrolysis process. Finally, the introduction of ZSM‐5 at 20 wt % results increased hydrocarbons (~3 wt %), furfurelas (~4 wt %) and reduced the phenols (~15 wt %), acid (~9 wt %) and oxygnetaed compounds. The present study showed that introducing zeolite catalysts improved pyrolysis products' properties.

Stable isotopic compositions and controlling factors of precipitation and atmospheric vapour in the headwaters of the Shule River

AbstractStable isotopic compositions of precipitation (δ18Op, δ2Hp and d‐excessp) and atmospheric vapour (δ18Ov, δ2Hv and d‐excessv) with high spatial–temporal resolution are crucial in revealing hydrologic cycle. Based on the variation characteristics of δ18Op/δ18Ov, δ2Hp/δ2Hv and d‐excessp/d‐excessv in the headwaters of the Shule River (HSR) on hourly and daily scales from June to September 2018, this study analysed the relationships between δ18Op/δ2Hp and δ18Ov/δ2Hv combined with the equilibrium fractionation model, as well as δ18Op/δ18Ov and meteorological factors. The slopes of local meteoric water line (LMWL) and the δ2Hv‐δ18Ov fitting equation were similar (7.96 and 7.94) with both intercepts exceeding 10, reflecting the great contribution of recycling moisture. The values of δ18Ov/δ2Hv were lower than δ18Op/δ2Hp but with consistent variation patterns throughout the period. The equilibrium simulation results suggested that precipitation and atmospheric vapour almost approached isotopic equilibrium state, especially during monsoon intrusion period. Affected by monsoon intrusion, the slopes and intercepts of the LMWLs and the δ2Hv‐δ18Ov fitting equations were smaller than those during non‐monsoon period and d‐excess and δ18O were negatively correlated. Relative humidity had significant negative correlations with δ18Op and δ18Ov in the whole period, however, the positive correlations between δ18Op/δ18Ov and temperature were observed during non‐monsoon and monsoon intrusion period, respectively. Our results demonstrated that precipitation and atmospheric vapour isotopic compositions exhibited consistency under the influence of diverse moisture sources, while more complex relationships were found between δ18Op/δ18Ov and meteorological factors. This research provided evidence for using the isotopic compositions of atmospheric vapour to indicate moisture sources, and can improve understanding of the water cycle and eco‐hydrological process from the perspective of the interaction between water and gas phases of the inland river basin in northwest China.

Vapor-Liquid Equilibrium Measurement of Systems Containing Glycerol for Separation Process of Glycerol as a By-Product of Biodiesel

The most popular technique to produce biodiesel were uses alcohol as a catalyst to transesterify triglycerides. The biodiesel transesterification process has a by-product in the form of glycerol which has a high selling value. Equilibrium data of glycerol and alcohol mixtures is limited in equilibrium conditions and systems which causes the glycerol purification process may not be designed and operated optimally. This research aims to obtain experimentally isobaric vapor-liquid equilibrium of methanol + glycerol binary system at 31.3, 61.3, and 100.8 kPa. A modified Glass Othmer-Still was utilised to carry out the experiment. Refractometer index type Bausch and Lomb ABBE was used to examine the equilibrium composition of the liquid and vapor phases. Using the L-W thermodynamic consistency test method, the experimental data used in this work were shown to be thermodynamically consistent. The experimental data were correlated well with the Wilson, Non-Random Two Liquid (NRTL), and Universal Quasi-Chemical (UNIQUAC) models with absolute average deviation in temperatures (AADT) and that in vapor compositions (AADy) smaller than 0.3% and 0.2%, respectively. The Universal Chemical Functional Group Activity Coefficient (UNIFAC) in predicting VLE the system studied showed good performance giving AADT and AADy smaller than 7.4% and 0.04%, respectively.

Understanding petroleum vapor fate and transport through high resolution analysis of two distinct vapor plumes

No field study has provided a detailed characterization of the molecular composition and spatial distribution of a vadose zone plume of petroleum volatile organic compounds (VOCs), which is critical to improve the current understanding of petroleum VOC transport and fate. This is study reports a high-resolution analysis of two distinct vapor plumes emanating from two different light non-aqueous phase liquid (LNAPL) sources (an aliphatic-rich LNAPL for Zone #1vs an aromatic-rich LNAPL for Zone #2) at a large petrochemical site. Although deep soil vapor signatures were similar to the source zone LNAPL signatures, the composition of the shallow soil vapors reflected preferential attenuation of certain hydrocarbons over others during upward transport in the vadose zone. Between deeper and shallower soil gas samples, attenuation of aromatics was observed under all conditions, but important differences were observed in attenuation to aliphatic compound classes. Attenuation of all aliphatic compounds was observed under aerobic conditions but little attenuation of any aliphatics was observed under anoxic conditions without methane. In contrast, under methanogenic conditions, paraffins attenuated more than isoparaffins and naphthenes. These results suggest that isoparafins and naphthenes may present more of a vapor intrusion risk than benzene or other aromatic hydrocarbons commonly considered to be petroleum vapor intrusion risk drivers. While the overall vapor composition changed significantly within the vadose zone, diagnostic ratios of relatively recalcitrant alkylcyclopentanes were preserved in shallow soil vapor samples. These alkylcyclopentanes may be useful for distinguishing between petroleum vapor intrusion and other sources of petroleum VOCs detected in indoor air.

From atmospheric water isotopes measurement to firn core interpretation in Adélie Land: a case study for isotope-enabled atmospheric models in Antarctica

Abstract. In a context of global warming and sea level rise acceleration, it is key to estimate the evolution of the atmospheric hydrological cycle and temperature in polar regions, which directly influence the surface mass balance of the Arctic and Antarctic ice sheets. Direct observations are available from satellite data for the last 40 years and a few weather data since the 1950s in Antarctica. One of the best ways to access longer records is to use climate proxies in firn or ice cores. The water isotopic composition in these cores is widely used to reconstruct past temperature variations. We need to progress in our understanding of the influence of the atmospheric hydrological cycle on the water isotopic composition of ice cores. First, we present a 2-year-long time series of vapor and precipitation isotopic composition measurement at Dumont d’Urville Station, in Adélie Land. We characterize diurnal variations of meteorological parameters (temperature, atmospheric water mixing ratio (hereafter humidity) and δ18O) for the different seasons and determine the evolution of key relationships (δ18O versus temperature or humidity) throughout the year: we find that the temperature vs. δ18O relationship is dependent on synoptic events dynamics in winter contrary to summer. Then, this data set is used to evaluate the atmospheric general circulation model ECHAM6-wiso (model version with embedded water stable isotopes) in a coastal region of Adélie Land where local conditions are controlled by strong katabatic winds which directly impact the isotopic signal. We show that a combination of continental (79 %) and oceanic (21 %) grid cells leads model outputs (temperature, humidity and δ18O) to nicely fit the observations, at different timescales (i.e., seasonal to synoptic). Therefore we demonstrate the added value of long-term water vapor isotopic composition records for model evaluation. Then, as a clear link is found between the isotopic composition of water vapor and precipitation, we assess how isotopic models can help interpret short firn cores. In fact, a virtual firn core built from ECHAM-wiso outputs explains much more of the variability observed in S1C1 isotopic record than a virtual firn core built from temperature only. Yet, deposition and post-deposition effects strongly affect the firn isotopic signal and probably account for most of the remaining misfits between archived firn signal and virtual firn core based on atmospheric modeling.

Isotopic Composition of Tropospheric Water Vapor in the Vicinity of St. Petersburg

Isotopic Composition of Tropospheric Water Vapor in the Vicinity of St. Petersburg