Fugacity Gradients Research Articles

Occurrence and diffusive air-seawater exchanges of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in Fildes Bay, King George Island, Antarctica

We report the levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in seawater and air, and the air-sea dynamics through diffusive exchange analysis in Fildes Bay, King George Island, Antarctica, between November 2019 and January 30, 2020. Hexachlorobenzene (HCB) was the most abundant compound in both air and seawater with concentrations around 39 ± 2.1 pg m−3 and 3.2 ± 2.4 pg L−1 respectively. The most abundant PCB congener was PCB 11, with a mean of 3.16 ± 3.7 pg m−3 in air and 2.0 ± 1.1 pg L−1 in seawater. The fugacity gradient estimated for the OCP compounds indicate a predominance of net atmospheric deposition for HCB, α-HCH, γ-HCH, 4,4′-DDT, 4,4′-DDE and close to equilibrium for the PeCB compound. The observed deposition of some OCs may be driven by high biodegradation rates and/or settling fluxes decreasing the concentration of these compounds in surface waters, which is supported by the capacity of microbial consortium to degrade some of these compounds. The estimated fugacity gradients for PCBs showed differences between congeners, with net volatilization predominating for PCB-9, a trend close to equilibrium for PCB congeners 11, 28, 52, 101, 118, 138, and 153, and deposition for PCB 180. Snow amplification may play an important role for less hydrophobic PCBs, with volatilization predominating after snow/glacier melting. As hydrophobicity increases, the biological pump decreases the concentration of PCBs in seawater, reversing the fugacity gradient to atmospheric deposition. This study highlights the potential impacts of climate change, through glacier retreat, on the biogeochemistry of POPs, remobilizing those compounds previously trapped within the cryosphere which in turn will transform the Antarctic cryosphere into a secondary source of the more volatile POPs in coastal areas, influenced by snow and ice melting.

Advanced modeling of diffusion and convection in multiphase compositional simulation for tight porous media

Small pore sizes influence the mass transport in gas enhanced oil recovery (EOR) in tight formations through complex phenomena such as diffusion and sorption. However, conventional simulators use relatively simple models for diffusion and sorption that do not properly represent non-ideal fluid interactions at high pressures. This paper presents a novel implementation of coupled diffusion and convection for multicomponent transport via the sorbed and bulk regions in tight porous media. Case studies highlight the important implication of convection in diffusion-dominant compositional transport in tight porous media.The simulator uses multicomponent diffusion based on the dusty-gas model (DGM), which uses the fugacity gradient as the driving force. The adsorption model used is an approximate solution based on the Multicomponent Potential Theory of Adsorption (MPTA) using the sorbed and central regions. The capillary pressure is included both in the flow equations and the flash calculations by minimizing the Helmholtz free energy using the Peng-Robinson equation of state at a fixed temperature, pore volume, and overall composition.A case study presents CO2 injection into a 1-D tight porous medium with a ternary mixture of methane, n-butane, and n-decane as the initial oil. Before CO2 injection, n-decane is most attracted to the pore wall and contained at a high concentration in the sorbed region. During CO2 injection, CO2 displaces n-decane from the pore wall, causing the counter-current transport of CO2 and n-decane.Simulation results show that the mixing of reservoir oil with CO2 in small pores results in local pressure changes, which tend to drive both diffusion and convection. In all cases, convection enhances multicomponent transport by dissipating these pressure changes. When CO2 is strongly attracted to the pore walls, a large pressure change on mixing accelerates the CO2 diffusion into the reservoir through the sorbed region and also the counter-current transport of oil components through the central region.

The effect of microplastics on the depuration of hydrophobic organic contaminants in Daphnia magna: A quantitative model analysis

Microplastics are emerging pollutants that can absorb large amounts of hydrophobic organic contaminants (HOCs). However, no biodynamic model has yet been proposed to estimate their effects on HOC depuration in aquatic organisms, where the HOC concentrations are time-varying. In this work, a microplastic-inclusive biodynamic model was developed to estimate the depuration of HOCs via ingestion of microplastics. Several key parameters of the model were redefined to determine the dynamic HOC concentrations. Through the parameterized model, the relative contributions of dermal and intestinal pathways can be distinguished. Moreover, the model was verified and the vector effect of microplastics was confirmed by studying the depuration of polychlorinated biphenyl (PCB) in Daphnia magna (D. magna) with different sizes of polystyrene (PS) microplastics. The results showed that microplastics contributed to the elimination kinetics of PCBs because of the fugacity gradient between the ingested microplastics and the biota lipids, especially for the less hydrophobic PCBs. The intestinal elimination pathway via microplastics would promote overall PCB elimination, contributing 37–41 % and 29–35 % to the total flux in the 100 nm and 2 μm polystyrene (PS) microplastic suspensions, respectively. Furthermore, the contribution of microplastic uptake to total HOC elimination increased with decreasing microplastic size in water, suggesting that microplastics may protect organisms from HOC risks. In conclusion, this work demonstrated that the proposed biodynamic model is capable of estimating the dynamic depuration of HOCs for aquatic organisms. The results can shed light on a better understanding of the vector effects of microplastics.

Application of multicomponent sorption for diffusive transport in numerical simulation of tight reservoirs

One of the main challenges in modeling compositional transport in tight formations is to include the complex interaction of chemical species with rock surfaces. Such interactions result in compositional variations near the surfaces, which can significantly affect the compositional diffusive transport through tight pores.This paper presents the application of the Multicomponent Potential Theory of Adsorption (MPTA) for the fluid compositions in the central and near-wall sorbed layers subject to a wall chemical potential. The two-layer approximation of MPTA is implemented in the diffusive transport simulation that computes the mass transfer driven by fugacity gradient based on the dusty gas model for the central and sorbed layers of pores. This simulator uses a partially implicit formulation to solve the multiphase multicomponent mass transfer equations including the sorbed layer.The main novelty of this paper lies in the detailed analysis of the interplay between fluid components and rock surfaces, which became possible with the two-layer MPTA coupled with multicomponent diffusion. The diffusion simulation for a ternary case of methane, n-butane, and n-decane with the approximate MPTA shows that the sorption and capillary pressure can cause the compositional segregation between the central and sorbed layers. The segregation enhances the rates of methane injection and n-decane production in their counter-current diffusion. Methane (the lightest) is transported deep into the reservoir by diffusing through the central layer while n-decane (the heaviest) is diffused primarily through the sorbed layer. n-Butane (the intermediate) does not show preferential partitioning into either layer, resulting in relatively inefficient transport. In the absence of sorption and capillary pressure, the countercurrent diffusion occurs between methane (the lightest) and n-butane (the intermediate) while n-decane (the heaviest) remains nearly immobile. That is, whether the simulation considers the surface-fluid interactions can substantially affect the compositional transport (e.g., produced fluid composition) through tight porous media.The multicomponent Langmuir model is often used for computing the sorbed excess in micropores. However, results show that the Langmuir model becomes physically inconsistent at high pressures because it predicts a monotonically increasing function of pressure. The new approach developed in this research is sufficiently flexible and reasonably accurate for modeling multicomponent sorption at high pressures.

Comprehensive Multi-compartment Sampling for Quantification of Long-Term Accumulation of PAHs in Soils.

Long-term accumulation in the soils of ubiquitous organic pollutants such as many polycyclic aromatic hydrocarbons (PAHs) depends on deposition from the atmosphere, revolatilization, leaching, and degradation processes such as photolysis and biodegradation. Quantifying the phase distribution and fluxes of these compounds across environmental compartments is thus crucial to understand the long-term contaminant fate. The gas-phase exchange between soil and atmosphere follows chemical fugacity gradients that can be approximated by gas-phase concentrations, yet which are difficult to measure directly. Thus, passive sampling, measured sorption isotherms, or empirical relationships to estimate sorption distribution have been combined in this study to determine aqueous (or gas) phase concentrations from measured bulk concentrations in soil solids. All these methods have their strengths and weaknesses but agree within 1 order of magnitude except for ex situ passive samplers employed in soil slurries, which estimated much lower concentrations in soil water and gas likely due to experimental artifacts. In field measurements, PAH concentrations determined in the atmosphere show a pronounced seasonality with some revolatilization during summer and gaseous deposition during winter, but overall dry deposition dominates annual mean fluxes. The characteristic patterns of PAHs in the different phases (gas phase, atmospheric passive samplers, bulk deposition, and soil solids) confirm the expected compound-specific distribution pattern and behavior. Since revolatilization fluxes in summer are only minor and wet and dry deposition is ongoing, our results clearly show that the PAH loads in topsoils will continue to increase.

A single-phase diffusion model for gas injection in tight oil reservoirs

This paper presents a mechanistic simulation study of one-dimensional multicomponent diffusion when the miscible injectant diffuses into a tight porous medium through the fracture/matrix interface with constant pore volume and temperature. The numerical implementation of diffusion based on the dusty gas model uses the fugacity gradient for each component in the mixture as the driving force to the diffusive flux. The Peng-Robinson equation of state is used to model the non-ideal interactions among components in the miscible diffusive process. Phase stability analysis by minimization of the Helmholtz free energy is performed for each grid block at every time step to ensure that mixtures are single-phase fluids throughout the simulation.The main novelty of this paper lies in the diffusion model and its theoretical analysis, in which the fluid non-ideality affects the multicomponent diffusion through two pathways: the fugacity coefficients and the volume change on mixing that causes local pressures to change under ultra-low permeability in tight porous media. Previous studies based on the Maxwell-Stefan model did not consider the latter pathway, while others based on Fick's law are even more simplistic by not considering the non-ideal chemical potential.Analysis in this research showed that the Maxwell-Stefan model was inconsistent with its own assumption of no pressure gradient when non-ideal mixing was considered for tight reservoirs. The dusty gas model does not have this issue because it allows for pressure gradients to drive mass transfer by Knudsen diffusion. The non-ideal interaction of components should be properly characterized and utilized to enhance the early-time flux through the fracture/matrix interface in miscible gas injection into a tight reservoir. Case studies show that the volume change on mixing may substantially increase local pressures and the rate of mass transfer in tight reservoirs. Also, the fugacity coefficients of oil components at infinite dilution in the solvent had a major influence on the rate of diffusion. These two factors highlight the importance of properly characterizing reservoir fluids through an equation of state.

Prediction of flexible pipe annulus composition by numerical modeling: identification of key parameters

This article describes recent improvements made in the design process of offshore flexible pipes. These improvements consider the more precise complex geometry and architecture of the flexible pipes, while considering their corrosive environment (high pressure, high temperature, acid gases (CO2, H2S), sea water, etc.) and the relevant physics. MOLDITM, the design software that was developed 20 years ago to predict flexible pipes annulus environment, has been constantly upgraded to increase its representativeness: use of chemical potential or fugacity to better describe the mass transport, improvement of the thermodynamic module to better describe the interaction between chemical species and allow to model the purging through gas release valves. Recently, a major advance has been made allowing to cope with flooded annulus flexible pipes. When the annulus is flooded, the tortuosity produced by the presence of steel wires inside the annulus can take a major importance. Therefore, a new model, named 3DIFF, has been developed to describe the 3-dimensional characteristics of the annulus and its impact on fugacity profile across the structure. Depending on permeation properties of each layer, the result is that the presence of water can produce a fugacity gradient within the annulus. This heterogeneity must be considered during the design process to be fully representative of service conditions and allow to select flexible pipes materials with confidence. Experimental devices used to generate permeation database are under constant evolution to study even more complex mechanisms such as the diffusion process in a flooded tortuosity or the compression effects of polymeric material on their permeation properties.

Effects of microplastics and food particles on organic pollutants bioaccumulation in equi-fugacity and above-fugacity scenarios

Microplastics (MPs), as emerging contaminants, sorb organic pollutants from the environment or leach out additives, thereby altering the fate of co-existing pollutants to organisms. We chose equi-fugacity and above-fugacity concentrations of polychlorinated biphenyls (PCBs) as background contamination and plastic additive concentrations, respectively, to investigate the effects of MPs on PCB bioaccumulation; we compared the effects of MPs with those of food-borne particles (FBPs). Co-exposure to MPs and FBPs at both the equi-fugacity and above-fugacity PCB concentrations had no obvious toxic effects (ROS generation and cyp1a expression) on zebrafish. When the zebrafish were exposed to the equi-fugacity PCB concentrations, the PCB concentrations reached 177.7–400.5 ng/g after a 7-d uptake; the presence of MPs did not significantly enhance PCB bioaccumulation. The remaining PCB concentrations in the fish after a 4-d depuration were 58.4–125.1 ng/g; the effects of MPs were the same as those during the uptake period. However, at the above-fugacity PCB concentrations, the MPs markedly increased the PCB bioaccumulation (by 1.8–fold) to 712.9 ng/g. This is because at above-fugacity concentrations, PCBs on MPs migrate to organisms as there were high fugacity gradients. The FBPs enhanced PCB bioaccumulation in zebrafish more effectively than the MPs, even after depuration. In the presence of FBPs, PCB bioaccumulation increased by 2.8- and 4.2- fold after uptake in the equi-fugacity and above-fugacity scenarios, respectively, both of which were significantly higher than that observed for the MPs. This is probably because FBPs are easily assimilated by fish, making the associated PCBs more bioavailable. Finally, during the co-existence of MPs and FBPs, MPs facilitate the depuration of PCBs accumulated via FBP vectors; conversely, FBPs did not affect PCB accumulation via MP vectors. Thus, this study elucidated the effects of MPs and FBPs on the bioaccumulation of pollutants at equi-fugacity or above-fugacity concentrations in aquatic environments.

From Explosive Vent Opening to Effusive Outpouring: Mineral Constraints on Magma Dynamics and Timescales at Paricutin Monogenetic Volcano

Abstract Paricutin volcano is the youngest monogenetic cone of the Michoacán–Guanajuato volcanic field (Mexico), with an excellent historical eruption record from February 1943 to March 1952. The magma emitted during the 9 years of activity was compositionally zoned from basaltic andesite to andesite. This eruption has been considered a classic example of magma differentiation controlled by crustal assimilation combined with fractional crystallization. However, a recent geochemical study of the eruption products points to mantle source heterogeneity and fractional crystallization as the key processes involved in the compositional variability of the magmas. Here we present a detailed petrological characterization of the minerals [olivine, plagioclase, pyroxene, Cr-spinel, and (Ti-)magnetite] to shed light on the processes that led to the chemical evolution of the eruptive products. Our sample set includes the early tephra from the first weeks or months of eruption and the whole sequence of lava flows that followed. The mineral assemblage, their texture, and chemical composition show a systematic evolution between the products from the opening of the explosive vent to the effusive stage. The early tephra are basaltic andesites with oscillatory-zoned olivine and plagioclase, zoned Cr-spinel, and rare pyroxene xenocrysts. In contrast, later erupted tephra and post-January 1944 lavas are basaltic andesites and andesites with normally zoned olivine, Cr-spinel inclusions in equilibrium with the host olivine, and frequent orthopyroxene (after December 1947) with minor chemical zoning. Mineral chemistry data and olivine diffusion timescales, together with whole-rock geochemistry, suggest a convective magma regime with large temperature and oxygen fugacity gradients characterized by short timescales (few days) during the opening stage, followed by a steadier magma regime with longer timescales (few months) and including periodic magma recharge, mixing, and fractional crystallization. In addition, the mineralogical evidence we have gathered does not support considerable crustal assimilation at Paricutin. This study shows that monogenetic eruptions are far from being geochemically simple, and instead involve multiple magma batches with complex storage and mixing stages before eruption.

Accumulation of HOCs via Precontaminated Microplastics by Earthworm Eisenia fetida in Soil.

Soil is a primary sink for plastics, but the influence of microplastics as carriers on terrestrial cycling of persistent contaminants is poorly understood as compared to aquatic systems. Studies to date have disregarded the potential fact that microplastics are generally contaminated before their entry into soil. In this study, earthworm Eisenia fetida was incubated for 28 d in a soil amended with five common types of microplastics precontaminated with polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) to elucidate contaminant transfer. Accumulation of HOCs in E. fetida varied greatly among different plastic types and HOCs. The freely dissolved concentration (Cfree) of HOCs showed that desorption of HOCs from microplastics into soil was closely related to plastic types and HOC hydrophobicity and was much slower for polystyrene or polypropylene than polyethylene. Biodynamic model analysis suggested that ingestion of microplastics could act as a significant pathway for some microplastics, likely due to HOCs on the plastics being in an "over-equilibrium" state. This was in contrast with mixing clean microplastics into HOC-contaminated soil, where the microplastics decreased bioaccumulation. Therefore, whether microplastics serve as facilitators or inhibitors of HOC bioaccumulation depends on the fugacity gradient of HOCs between microplastics and soil, which highlights the importance of considering the sequence of contamination between the plastics and soil. These findings also question the validity of short-term experiments because of the generally very slow partition kinetics of HOCs on plastics.

Crystals reveal magma convection and melt transport in dyke-fed eruptions

The processes and ranges of intensive variables that control magma transport and dyke propagation through the crust are poorly understood. Here we show that textural and compositional data of olivine crystals (Mg/Fe, Ni and P) from the tephra of the first months of Paricutin volcano monogenetic eruption (Mexico, 1943–1952) record fast growth and large temperature and oxygen fugacity gradients. We interpret that these gradients are due to convective magma transport in a propagating dyke to the Earth’s surface in less than a few days. The shortest time we have obtained is 0.1 day, and more than 50% of the calculated timescales are < 2 days for the earliest erupted tephra, which implies magma ascent rates of about 0.1 and 1 m s−1. The olivine zoning patterns change with the eruptive stratigraphy, and record a transition towards a more steady magma flow before the transition from explosive to effusive dynamics. Our results can inform numerical and experimental analogue models of dyke propagation, and thus facilitate a better understanding of the seismicity and other precursors of dyke-fed eruptions.

Processes and Conditions of the Origin for Fe3+-Bearing Magnesiowüstite under Lithospheric Mantle Pressures and Temperatures

An experimental study, implicated in the revealing of the conditions for the origin for Fe3+-bearing magnesiowüstite in the lithospheric mantle, was performed using Mössbauer spectroscopy of pre-synthesized samples. Experiments were carried out using a multi-anvil high-pressure split-sphere apparatus at 6.3–7.5 GPa, in the range of 1100–1650 °C in carbonate-metal, carbonate–oxide-metal, carbonate-oxide, carbide-oxide and carbonate–metal- sulphur systems. In three experimental series, oxygen fugacity gradient in the samples was created, which enabled the study of the processes of magnesiowüstite formation under oxidizing and reducing conditions (ΔlogfO2 (FMQ) values from −1 to −5). It was established that Fe3+-bearing magnesiowüstite can form both in assemblage with oxidized phases, such as carbonate or with reduced ones—metal, carbides, sulphides, graphite and diamond. According to the Mössbauer spectroscopy, the composition of synthesized magnesiowüstite varied within a range of Fe3+/ΣFe values from 0 to 0.3, with IV and VI coordination of Fe3+ depending on P, T, fO2, x-parameters. It was established that Fe3+-bearing magnesiowüstite formation processes under upper mantle P,T-conditions include redox reactions, with magnesiowüstite being (1) reductant or (2) product of interaction, (3) crystallization processes of magnesiowüstite from an oxidized melt, where magnesiowüstite acts as a sink for ferric iron and (4) iron disproportionation.

Longitudinal dynamics of high baryon density matter in high-energy heavy-ion collisions

In high energy heavy-ion collisions, the two colliding nuclei pass through each other leaving behind an almost baryon free central rapidity region. Most of the baryons are carried away by the nuclear remnants and are located in the so-called fragmentation regions. In previous papers \cite{Li:2016wzh,Li:2018ini}, it has been argued that very high baryon densities, more than ten times larger than the normal nuclear density, can be achieved in these fragmentation regions. In this paper, we assume the high baryon density matter is thermalized at the same time as the baryon-free quark-gluon plasma in the central rapidity region. We perform a 1+1D (temporal + longitudinal) hydrodynamic simulation covering both the fragmentation regions and the central rapidity region with the baryon diffusion equation included. Baryons are found to diffuse from the fragmentation regions to the central rapidity region driven by fugacity gradients. The baryon chemical potential at freezeout monotonically increases from the central rapidity region to the fragmentation regions, suggesting a rapidity scan in high energy heavy-ion collisions might be helpful in searching for the critical point of the QCD phase diagram.

Modeling hydrocarbon droplet dissolution in near-critical or supercritical water using GCA-EOS and non-ideal diffusional driving force in binary mixtures

In this work, the mixing of a hydrocarbon droplet in near- and super-critical water (NCW/SCW) is mathematically modeled, coupling thermodynamic properties calculation with transport processes. In non-ideal systems, mass transfer is captured using the generalized Maxwell-Stefan equations with the driving force expressed in terms of the fugacity gradients. The GCA-EOS is used to predict the thermodynamic properties and phase equilibrium compositions. We select n-decane, n-triacontane, benzene, naphthalene and 1-decylnaphthalene as representative hydrocarbons. Our simulations show delayed mixing processes as the temperature approaches the upper critical solution temperature (UCST) of the mixture, consistent with the impact of non-ideal diffusional driving forces evaluated from pure thermodynamic calculations. Results also show that the phase behavior notably affects the non-ideal driving forces near the UCST, which confirms the importance of coupling accurate thermodynamic models in predictive mixing studies.

Re-Equilibration Processes in Fluid Inclusion Assemblages

Post-entrapment modifications reduce the reliability of fluid inclusions to determine trapping conditions in rock. Processes that may modify fluid inclusion properties are experimentally identified in this study using synthetic fluid inclusions in quartz with a well-defined composition and density. Modifications are characterized with microthermometry (homogenization and dissolution temperatures) and Raman-spectroscopy in binary fluid systems H2O-D2O and H2O-NaCl. Three distinct processes were identified in this study: (1) diffusion of H2O and D2O; (2) crystal-recovery, expulsion of H2O and accumulation of quartz in inclusions (preferential H2O loss); (3) irreversible total volume increase at the α-β quartz transition. Diffusion is caused by H2O fugacity gradients and can be modelled according to classical diffusion models. The variability of re-equilibrated properties in fluid inclusion assemblages depends on time, temperature, diffusion distance and the size of fluid inclusions. Negative pressure gradients (internal under-pressure) induce the crystal-recovery process, in which H2O is preferentially extracted from inclusions that simultaneously shrink by the inward growth of quartz. This process reduces the H2O concentration and increases the fluid density by total volume loss. Temperature and time are also controlling factors of this process, which is able to transport H2O against fugacity gradients.

Fugacity gradients of hydrophobic organics across the air-water interface measured with a novel passive sampler

Mass transfer of hydrophobic organic contaminants (HOCs) across the air-water interface is an important geochemical process controlling the fate and transport of HOCs at the regional and global scales. However, few studies have characterized concentration or fugacity profiles of HOCs near both sides of the air-water interface, which is the driving force for the inter-compartmental mass transfer of HOCs. Herein, we introduce a novel passive sampling device which is capable of measuring concentration (and therefore fugacity) gradients of HOCs across the air-water interface. Laboratory studies indicated that the escaping fugacity values of polycyclic aromatic hydrocarbons (PAHs) from water to air were negatively correlated to their volatilization half-lives. Results for field deployment were consistent between the passive sampler and an active method, i.e., a combination of grab sampling and liquid-liquid extraction. In general, the fugacity profiles of detected PAHs were indicative of an accumulation mechanism in the surface microlayer of the study regions (Haizhu Lake and Hailing Bay of Guangdong Province, China), while p,p'-DDD tended to volatilize from water to the atmosphere in Hailing Bay. Furthermore, the fugacity profiles of the target analytes increased towards the air-water interface, reflecting the complexity of environmental behavior of the target analytes near the air-water interface. Overall, the passive sampling device provides a novel means to better characterize the air-water diffusive transfer of HOCs, facilitating the understanding of the global cycling of HOCs.

Seasonal variation in diffusive exchange of polycyclic aromatic hydrocarbons across the air–seawater interface in coastal urban area

Concentrations of 15 polycyclic aromatic hydrocarbons (PAHs) in air–seawater interface were measured over 1year in the coastal region of Incheon, South Korea. Most individual PAHs and total PAHs in air displayed statistically significant negative correlations with temperature, but not significant in seawater. Less hydrophobic compounds with three rings were at or near equilibrium in summer, while PAHs with four to six rings were in disequilibrium in all seasons, with higher fugacity gradients in colder seasons and for more hydrophobic compounds. Differently from fugacity gradients, the highest net fluxes occurred for some three- and four-ring PAHs showing the highest atmospheric concentrations. Net gaseous exchange, which was higher in winter, occurred from air to seawater with an annual cumulative flux of 2075μg/m2/year (for Σ15PAHs), indicating that atmospheric PAHs in this region, originating from coal/biomass combustion, can deteriorate the quality of seawater and sediment.

Salinity and density modifications of synthetic H2O and H2O–NaCl fluid inclusions in re-equilibration experiments at constant temperature and confining pressure

Experiments have been performed to elucidate post-entrapment modifications of natural fluid inclusions. Synthetic H2O and H2O–NaCl fluid inclusions in quartz were re-equilibrated at 599.7–600.7°C and 332.6–338.3MPa in hydrothermal autoclaves, and subjected to H2O fugacity gradients at similar temperature and hydrostatic pressure conditions to those of the original syntheses. Individual inclusions in specific assemblages were analyzed in detail, i.e. size, shape, depth, homogenization and ice-dissolution temperatures, before and after the re-equilibration experiments. Accurate loading and unloading of the samples along isochoric T–p paths require monitoring the temperature at the sample within the autoclaves. Multiple loading and un-loading of the samples along these paths do not affect the properties of fluid inclusions. Synthetic H2O fluid inclusions are not modified after re-equilibration in a pure H2O fluid, but reveal significantly higher homogenization temperatures after re-equilibration in 20mass% NaCl solution. Synthetic NaCl–H2O fluid inclusions with 10, 16.3 and 19.8mass% NaCl reveal higher salinities after re-equilibration in a pure H2O fluid, and highly variable homogenization temperatures: positive as well as negative modifications. The magnitude of modifications indicates that two processes must have operated simultaneously to obtain the observed homogenization and dissolution temperatures in individual inclusions: (1) preferential H2O loss via diffusion; and (2) total volume loss by diffusion of quartz into the former inclusion volume. These processes are inconsistent with the expected H2O diffusion into inclusions according to the applied fugacity gradients in the experimental setup. These simultaneously operating processes are suggested to be the main modification method of natural fluid inclusions in a variety of experimental settings and in geological environments.

Impact of non-ideality on mixing of hydrocarbons and water at supercritical or near-critical conditions

The mixing of a single-component or multi-component hydrocarbon (HC) droplet in supercritical or near-critical water (SCW/NCW) is modeled. Transport, thermodynamics, and phase equilibrium sub-models are used to estimate the relevant physical properties. We use a generalized Maxwell–Stefan (MS) expression to model the multi-component mass transfer and a diffusion driving force expressed in terms of fugacity gradients to account for effects of non-ideality on mass fluxes. We compare the ideal and non-ideal diffusive driving forces for different mixing conditions and different HCs, and show that when the mixing temperature is close to or greater than the upper critical solution temperature (UCST), the non-ideal driving force model predicts a much slower mixing process and higher concentrations of the heavier HC than the ideal driving force, due to the presence of a diffusion barrier captured by the non-ideal driving force model.

Re-equilibration of natural H2O–CO2–salt-rich fluid inclusions in quartz—Part 1: experiments in pure water at constant pressures and differential pressures at 600 °C

Re-equilibration processes of natural H2O–CO2–NaCl-rich fluid inclusions quartz are experimentally studied by exposing the samples to a pure H2O external fluid at 600 °C. Experimental conditions are selected at nearly constant pressure conditions (309 MPa) between fluid inclusions and pore fluid, with only fugacity gradients in H2O and CO2, and at differential pressure conditions (394–398 MPa, corresponding to an internal under-pressure) in addition to similar CO2 fugacity gradients and larger H2O fugacity gradients. Modifications of fluid inclusion composition and density are monitored with changes in ice dissolution temperature, clathrate dissolution temperature and volume fraction of the vapour phase at room temperature. Specific modification of these parameters can be assigned to specific processes, such as preferential loss/gain of H2O and CO2, or changes in total volume. A combination of these parameters can clearly distinguish between modifications according to bulk diffusion or deformation processes. Bulk diffusion of CO2 according to fugacity gradients is demonstrated at constant pressure conditions. The estimated preferential loss of H2O is not in accordance with those gradients in both constant pressure and differential pressure experiments. The development of deformation halos in quartz around fluid inclusions that are either under-pressurized or over-pressurized promotes absorption of H2O from the inclusions and inhibits bulk diffusion according to the applied fugacity gradients.