Plume Dispersion Research Articles

High-fidelity CFD modeling of pollutant dispersion from aircraft auxiliary power units (APUs) at a realistic airport and the effects on airport air quality

Many studies have investigated air-traffic impact on airport air quality through main-engine emissions, however very few have characterized the APU-related impact. As field-monitoring remains limited, our study used CFD simulations to provide a high-fidelity representation of 19 APU dispersion plumes in a realistic airport configuration. Results of three dominant wind configurations show that the global dispersion plume (from all APUs) was transported by incident winds. Depending on wind direction, pollutant trapping within a large downwash region was observed downstream of the terminal-building. Local differences were observed depending on source locations; emissions within the downwash region were pushed against the terminal-facade which promoted emission spillover on terminal-roof, while plumes within the unperturbed boundary layer were transported by incident winds. Quantitatively, APU pollutant concentrations dropped overall by 3–4 orders of magnitude around the terminal-building, while diluted concentrations by 5–6 orders of magnitude were monitored at the airport exit. Given source concentrations with an appropriate experimental apparatus, this model can serve as an airport air quality decision-making tool to finely characterize individual source impacts. Such information can help assist airport operation management (taxi to gate/runway, gate assignment, safe corridors for ground-handling personnel) so as to reduce/prevent the impact of pollutant hot spots depending on wind configurations.

Study of turbulent dispersion of a concentration plume emitting from a line source over a rib‐roughened surface

Turbulent dispersion of a concentration plume emitting from a horizontal line source over a rib-roughened surface has been studied using direct numerical simulations (DNS). Four test cases have been compared to investigate the effects of the source elevation and location on the plume dispersion in a turbulent boundary layer. The transport process of the concentration is investigated in both physical and spectral spaces which includes analyses of statistical moments of the concentration field, decay rate, plume width, pre-multiplied spectra of the velocity and concentration fields, and the probability density function (PDF) of concentration fluctuations. It is observed that as the mean plume development enters the long-range dispersion stage, the decay rate of the mean concentration field begins to feature a constant slope of −3/2, while the vertical spread of the mean plume exhibits a constant slope of 1/3 in all four line source release cases in a ribbed wall flow. It is also observed that the profiles of both the mean concentration field and the RMS of concentration fluctuations exhibit a self-similarity pattern downstream of the line source in all four test cases. By comparing the characteristic length scales of the spanwise velocity and scalar fields, two distinct stages of the instantaneous plume development are observed, dominated by the turbulent convective and diffusive mechanisms. It is discovered that the transition from the turbulent convective stage to the turbulent diffusive stage occurs more rapidly for line sources placed near the wall and inside the cavities.

Hydrogen Leakage Simulation and Risk Analysis of Hydrogen Fueling Station in China

Hydrogen is a renewable energy source with various features, clean, carbon-free, high energy density, which is being recognized internationally as a “future energy.” The US, the EU, Japan, South Korea, China, and other countries or regions are gradually clarifying the development position of hydrogen. The rapid development of the hydrogen energy industry requires more hydrogenation infrastructure to meet the hydrogenation need of hydrogen fuel cell vehicles. Nevertheless, due to the frequent occurrence of hydrogen infrastructure accidents, their safety has become an obstacle to large-scale construction. This paper analyzed five sizes (diameters of 0.068 mm, 0.215 mm, 0.68 mm, 2.15 mm, and 6.8 mm) of hydrogen leakage in the hydrogen fueling station using Quantitative Risk Assessment (QRA) and HyRAM software. The results show that unignited leaks occur most frequently; leaks caused by flanges, valves, instruments, compressors, and filters occur more frequently; and the risk indicator of thermal radiation accident and structure collapse accident caused by overpressure exceeds the Chinese individual acceptable risk standard and the risk indicator of a thermal radiation accident and head impact accident caused by overpressure is below the Chinese standard. On the other hand, we simulated the consequences of hydrogen leak from the 45 MPa hydrogen storage vessels by the physic module of HyRAM and obtained the ranges of plume dispersion, jet fire, radiative heat flux, and unconfined overpressure. We suggest targeted preventive measures and safety distance to provide references for hydrogen fueling stations’ safe construction and operation.

Iron ligands and isotopes in hydrothermal plumes over backarc volcanoes in the Northeast Lau Basin, Southwest Pacific Ocean

Deep-sea hydrothermal venting is an important source of dissolved iron (dFe) to the oceans. Fe isotopes can be used as a potential tool to trace the dispersal of hydrothermal plumes. However, Fe isotope fractionation and its relation with Fe speciation as hydrothermal plumes disperse is still poorly constrained. In this study, we determined the Fe speciation and total and dissolved Fe isotope composition (δ56tFe, δ56dFe) for several hydrothermal plumes from backarc volcanoes in the Northeast Lau Basin. This combined approach provides important insights into the evolution of Fe isotopes in hydrothermal plumes. The results suggest δ56tFe variation in plumes is related to the loss of particulate Fe-sulfides or Fe-oxyhydroxides (FeOOH), both of which are dependant on the H2S concentrations and Fe/H2S in the source hydrothermal fluids. δ56dFe compositions in the hydrothermal plumes increase during plume dispersal/dilution and can be as high as 0.85 ‰, demonstrating that hydrothermal plumes can export dissolved Fe with a significantly heavier δ56dFe than hydrothermal fluids. The reasons may be ascribed to the organic Fe complexes (FeL) and colloidal FeOOH in the dissolved phase. Another interpretation might be associated with the low pH in volcanic arc hydrothermal systems rich in magmatic CO2 and SO2, which decreases the Fe(II) oxidation rate. Further, we demonstrate for the first time that the δ56dFe is positively correlated with the conditional stability constants of FeL (logKʹFeL). A Rayleigh distillation model is presented based on the mass balance of the determined FeL, and colloidal FeOOH in hydrothermal plumes, which can explain the observed Fe isotope compositions in hydrothermal plumes. Our data show how Fe isotopes are transformed within a hydrothermal plume above arc volcanoes and how these may differ from that of the original vent fluids. It adds to our understanding of the processes that have an impact on the Fe speciation and isotope composition in deep-sea hydrothermal plumes.

Measurements and modelling of the three-dimensional near-field dispersion of particulate matter emitted from passenger ships in a port environment

The maritime sector poses significant challenges in controlling the emission of harmful pollutants, such as particulate matter, and reducing their impact on coastal areas and the atmospheric environment. Efforts to regulate the sector necessitate new knowledge and methods to characterise the evolution and physicochemical transformation of maritime particle emissions dispersing in port areas. An experimental campaign at the Port of Rafina, Greece, was conducted with this in mind. In this paper, we report on the first multi-characteristic particle measurements, including particle number (PN), lung deposited surface area (LDSA), and black carbon (BC), performed at both land and sea using a novel instrument set-up mounted on an unmanned aerial vehicle (UAV). Land-based measurements showed that LDSA averages, which are influenced by particle number and size, increase up to 20 times above background levels as an emission plume progresses downwind, whereas BC concentrations, which are dominated by mass, are ∼12 times higher than the background concentration. Ground and UAV-based particle comparisons showed that PN and LDSA measurements exhibit greater differences than BC relative to the plume's location. Ground-based sensors had ∼50% lower LDSA and PN concentrations, whereas BC was about equal. The experimental observations are further substantiated by coupling a Gaussian plume dispersion model and a new computationally attractive approach, known as the Incompletely Stirred Reactor Network (ISRN) method, to predict the three-dimensional evolution of particle characteristics considering the effects of dilution, segregation, and physicochemical transformations, such as coagulation. Based on simplifying assumptions for the particle size distribution sources within the port area, the ISRN estimates suggest that the discrepancy between various metrics can be partly explained by coagulation, responsible for a non-linear increase in particle size, depending on the local level of dilution and mixing intensity, leading up to a ∼25% decrease in PN and LDSA compared to BC. Combined, measurements and modelling highlight the effect of the sampling location and the importance of monitoring more than one particle metric to characterise particle evolution.

Satellite assessment of coastal plume variability and its relation to environmental variables in the Sofala Bank

Monthly composites of remote sensing reflectance at 555 nm wavelength (Rrs555) from ocean color imagery of the MODIS sensor onboard the Aqua platform were used to characterize the spatial and temporal variability of coastal plume in the Sofala Bank and its relation to river discharge, local rainfall, and wind speed. To achieve the objective, maps of monthly composites of Rrs555 over the Sofala Bank were inspected and statistical analysis was performed, including correlation, analysis of variance, and wavelet coherence between environmental variables and both plume area and Rrs555. Climatology of Rrs555 revealed that both plume dispersion and Rrs555 values are higher during June to December and lower during January to May. A positive correlation (r = 0.77) between wind speed and monthly time series of Rrs555, and a negative correlation between the Zambezi river discharge (r = −0.21) and rainfall (r = −0.67) with Rrs555 were found. These results suggest that variation of suspended matter in the Sofala Bank is mainly controlled by erosion and re-suspension by winds rather than the input of terrigenous matter by the Zambezi River discharge and rainfall, assuming that Rrs555 can be a valid proxy for the inorganic suspended matter. The southern portion of the Sofala Bank (i.e., near the mouths of the Pungue and Buzi Rivers) presented higher values of Rrs555 if compared to the center region near Zambezi river mouth and the northern region near Licungo river mouth. The higher Rrs555 values in the southern region might be associated with higher re-suspension rates due to increased tide mixing, dredging activities, and the shallower nature of bathymetry in the southern region. The dominance of wind in controlling the variability of suspended sediments and the eventual relatively greater contribution of Pungue and Buzi River than the Zambezi in supplying sediments could represent an evidence of weakening of Zambezi River supply of sediments, a process that might have started after damming the Zambezi Catchment.

Visualizing Groundwater Dispersion: Laboratory Exercise on Dispersivity with Hands-on and Online Students

Longitudinal groundwater dispersion is measured by calculating the spreading of a solute in the direction of groundwater flow as a function of time, with dispersivity being the plume dispersion divided by the groundwater velocity. Two-dimensional physical groundwater flow models were used in a laboratory exercise to illustrate groundwater dispersion to hands-on and online students. Learning assessment of the pedagogical value of the laboratory exercise was based on a student survey and an independent laboratory assignment graded by the course instructor. Both tools indicated that student learning was effectively enhanced by the dispersivity laboratory exercise; however, it was more effective for the hands-on students.

Modelling the Dispersion of Seafloor Massive Sulphide Mining Plumes in the Mid Atlantic Ridge Around the Azores

It is increasingly recognised that deep-sea mining of seafloor massive sulphides (SMS) could become an important source of mineral resources. These operations will remove the targeted substrate and produce potentially toxic plumes from in situ seabed excavation and from the return water pumped back down to the seafloor. However, the spatial extent of the impact of deep-sea mining is still uncertain because few field experiments and models of plume dispersion have been conducted. In this study, we used three-dimensional hydrodynamic models of the Azores region together with a theoretical commercial mining operation of polymetallic SMS to simulate the potential dispersal of plumes originating from different phases of mining operations, and to assess the magnitude of potential impacts. Although the model simulations presented here were subject to many caveats, they did reveal some important patterns. The model projected marked differences among sites making generalisations about plume-dispersal patterns in mid-ocean ridges difficult. Nevertheless, the models predicted large horizontal and vertical plume-dispersals above the thresholds adopted. Persistent plumes (temporal frequency >50%, i.e., 6 months out of 12 months) were projected to disperse an average linear distance of 10 to 20 km, cover an area of 17 to 150 km2, and extend more than 800 m in the water column. In fact, the model projected that plumes may disperse beyond the licensed mining areas, reach the flanks and summits of nearby topographic features, and extend into the bathypelagic, mesopelagic, and epipelagic environments. Modelled plume-dispersal overlaps with the predicted distribution of cold-water corals and with existing fishing activities. These potential impacts would be of particular concern in regions such as the Azores, where local populations are highly dependent on the sea for their livelihoods. The findings of this study are an important initial step towards understanding the nature and magnitude of deep-sea mining impacts in space and time.

The Lagrangian Atmospheric Radionuclide Transport Model (ARTM) — development, description and sensitivity analysis

Atmospheric dispersion models are applied to describe and predict the dispersion of emitted plumes. Here, we describe the Lagrangian Atmospheric Radionuclide Transport Model (ARTM) 2.8.0 which was developed to simulate the atmospheric dispersion of the emissions of nuclear facilities under routine operation for regulatory purposes over annual time scales. ARTM includes a diagnostic wind field model and a particle dispersion model. It simulates size-dependent wet and dry deposition, plume rise and γ-cloud shine of radioactive exhaust plumes in the simulation domain. This work presents an extensive overview of the different components of the model and of the physical and mathematical concepts of ARTM. We investigate the dependence of the plume dispersion in terms of plume volume, position of maximum concentration and dry deposition rates on key input parameters such as atmospheric stability, surface roughness, zero plane displacement height, source height and the particle size in the case of particulate matter tracers. The results indicate a strong dependence of plume volume and position of the maximum concentration on the stability as well as a minor influence on surface roughness. The source height above ground level has a low impact on the plume volume as the zero plane displacement only slightly affects the position of maximum concentration. Strong turbulence under unstable conditions tends to reduce the impact of sedimentation and decreases deposition in general. This computational model serves to advance the understanding of the dispersion of radioactive plumes in the boundary layer.

A novel experimental chamber for the characterization of free-falling particles in volcanic plumes.

Volcanic plumes pose a hazard to health and society and a particular risk for aviation. Hazard mitigation relies on forecasting plume dispersion within the atmosphere over time. The accuracy of forecasts depends on our understanding of particle dispersion and sedimentation processes, as well as on the accuracy of model input parameters, such as the initial particle size distribution and concentrations of volcanic particles (i.e., volcanic ash) in the atmosphere. However, our understating of these processes and the accurate quantification of input parameters remain the main sources of uncertainty in plume dispersion modeling. It is usually impractical to sample volcanic plumes directly, but particle sedimentation can be constrained in the laboratory. Here, we describe the design of a new experimental apparatus for investigating the dynamics of free-falling volcanic particles. The apparatus can produce a sustained column of falling particles with variable particle concentrations appropriate to a volcanic plume. Controllable experimental parameters include particle size distributions, types, and release rates. A laser-illuminated macrophotography system allows imaging of in-flight particles and their interactions. The mass of landing particles is logged to inform deposition rates. Quantitative measurements include particle morphology characterization, settling velocities, flow rates, and estimation of concentrations. Simultaneous observations of particle interaction processes and settling dynamics through direct control over a wide range of parameters will improve our parameterization of volcanic plume dynamics. Although the apparatus has been specifically designed for volcanological investigations, it can also be used to explore the characteristics of free-falling particle columns occurring in both environmental and industrial settings.

Assessing the representativity of NH<sub>3</sub> measurements influenced by boundary-layer dynamics and the turbulent dispersion of a nearby emission source

Abstract. This study presents a fine-scale simulation approach to assess the representativity of ammonia (NH3) measurements in the proximity of an emission source. Close proximity to emission sources (< 5 km) can introduce a bias in regionally representative measurements of the NH3 molar fraction and flux. Measurement sites should, therefore, be located a significant distance away from emission sources, but these requirements are poorly defined and can be difficult to meet in densely agricultural regions. This study presents a consistent criterion to assess the regional representativity of NH3 measurements in proximity to an emission source, calculating variables that quantify the NH3 plume dispersion using a series of numerical experiments at a fine resolution (20 m). Our fine-scale simulation framework with explicitly resolved turbulence enables us to distinguish between the background NH3 and the emission plume, including realistic representations of NH3 deposition and chemical gas–aerosol transformations. We introduce the concept of blending distance based on the calculation of turbulent fluctuations to systematically analyze the impact of the emission plume on simulated measurements, relative to this background NH3. We perform a suite of systematic numerical experiments for flat homogeneous grasslands, centered around the CESAR Observatory at Cabauw, to analyze the sensitivity of the blending distance, varying meteorological factors, emission/deposition and NH3 dependences. Considering these sensitivities, we find that NH3 measurements at this measurement site should be located at a minimum distance of 0.5–3.0 and 0.75–4.5 km from an emission source for NH3 molar fraction and flux measurements, respectively. The simulation framework presented here can easily be adapted to local conditions, and paves the way for future ammonia research to integrate simulations at high spatio-temporal resolutions with observations of NH3 concentrations and fluxes.

Evaluation of a Revised AERMOD Treatment of Plume Dispersion in the Daytime Elevated Stable Layer

Advanced dispersion models such as AERMOD specifically address the portion of a plume emitted in convective conditions that is sufficiently buoyant to rise into the stable layer above the elevated inversion. This portion of the plume mass is often referred to as the “penetrated plume” because that plume component breaks through the elevated inversion and penetrates into the stable layer aloft. A pre-mature mixing of the penetrated plume to the ground has been identified in the current formulation of AERMOD, which is the USEPA-preferred short-range dispersion model and used in several other countries. This behavior has been observed based on data from field studies where the model is found to overpredict ground-level concentration events due to the penetrated plume component, with the timing of these peak predictions too early in the day. A proposed update to AERMOD to address the penetrated plume issue (referred to as “HBP” for modifications particularly important for “highly buoyant plume”) is documented and evaluated in this manuscript. The revised approach involves a check on the convective mixing height for the current hour as well as the next hour to determine how much of the penetrated plume has been captured by the convective boundary layer by the end of the current hour. The amount of the penetrated plume mass that is allowed to mix to the ground in the HBP modifications depends upon the result of this calculation. The HBP modification has been evaluated as an update to AERMOD for 3 databases along with a sensitivity analysis of the effects of the HBP changes on a variety of stack heights and buoyancy fluxes. The findings of the evaluation indicate that the HBP changes to AERMOD result in reduced overprediction tendencies. “Implications Statement” for the HBP paper being submitted to JAWMA A proposed enhancement to AERMOD to address a pre-mature mixing of penetrated plume material to the ground has been performed by implemented and evaluated by the authors. The enhancement, referred to as the highly buoyant plume (HBP) is based on work developed by Dr. Jeffrey Weil. HBP is designed to better characterize the penetrated plume behavior in the model such that it aligns more closely with observations based on data from field studies.

Strontium, Hydrogen and Oxygen Behavior in Vent Fluids and Plumes from the Kueishantao Hydrothermal Field Offshore Northeast Taiwan: Constrained by Fluid Processes

Strontium (Sr), hydrogen (H) and oxygen (O) in vent fluids are important for understanding the water–rock interaction and hydrothermal flux in hydrothermal systems. We have analyzed the Sr, H and O isotopic compositions of seawater, vent fluid and hydrothermal plume samples in the Kueishantao hydrothermal field, as well as their calcium (Ca), total sulfur (S), Sr, arsenic (As), stibium (Sb), chlorine (Cl) and manganese (Mn) concentrations for understanding the origin and processes of fluids. The results suggest that most As, Sb and Mn are leached from andesitic rocks into the fluids, and most Ca and Cl remained in the deep reaction zone during the fluid–andesitic rock interaction. The ranges of 87Sr/86Sr, δDV-SMOW and δ18OV-SMOW values in the yellow spring, white spring and plumes are small. The 87Sr/86Sr, δDV-SMOW and δ18OV-SMOW values of fluids and plumes are like those of ambient seawater, indicating that the Sr, H and O of vent fluids and hydrothermal plumes are derived primarily from seawater. This suggests that the interaction of andesite and subseafloor fluid is of short duration and results in the majority of As, Sb and Mn being released into fluids, while most Ca and Cl remained in the deep reaction zone. In addition, there was no significant variation of Sr, H and O isotopic compositions in the upwelling fluid, keeping the similar isotopic compositions of seawater. There are obvious correlations among the pH values, As and Sb concentrations, and H isotopic compositions of the vent fluids and hydrothermal plumes, implying that the As and Sb concentrations and H isotopic compositions can trace the dispersion of plumes in the ambient seawater. According to the Sr concentrations and 87Sr/86Sr values, the water/rock ratios are 3076~8124, which is consistent with the idea that the interaction between fluid and andesite at the subseafloor is of short duration. The hydrothermal flux of Sr discharged from the yellow spring into the seawater is between 2.06 × 104 and 2.26 × 104 mol/yr, and the white spring discharges 1.18 × 104~1.26 × 104 mol/yr Sr if just andesites appear in the reaction zone.

Evaluation of two common source estimation measurement strategies using large-eddy simulation of plume dispersion under neutral atmospheric conditions

Abstract. This study uses large-eddy simulations (LESs) to evaluate two widely used observational techniques that estimate point source emissions. We evaluate the use of car measurements perpendicular to the wind direction and the commonly used Other Test Method 33A (OTM 33A). The LES study simulates a plume from a point source released into a stationary, homogeneous, and neutral atmospheric surface layer over flat terrain. This choice is motivated by our ambition to validate the observational methods under controlled conditions where they are expected to perform well since the sources of uncertainties are minimized. Three plumes with different release heights were sampled in a manner that mimics sampling according to car transects and the stationary OTM 33A. Subsequently, source strength estimates are compared to the true source strength used in the simulation. Standard deviations of the estimated source strengths decay proportionally to the inverse of the square root of the number of averaged transects, showing statistical independence of individual samples. The analysis shows that for the car transect measurements at least 15 repeated measurement series need to be averaged to obtain a source strength within 40 % of the true source strength. For the OTM 33A analysis, which recommends measurements within 200 m of the source, the estimates of source strengths have similar values close to the source, which is caused by insufficient dispersion of the plume by turbulent mixing close to the source. Additionally, the derived source strength is substantially overestimated with OTM 33A. This overestimation is driven by the proposed OTM 33A dispersion coefficients, which are too large for this specific case. This suggests that the conditions under which the OTM 33A dispersion constants were derived were likely influenced by motions with length scales beyond the scale of the surface layer. Lastly, our simulations indicate that, due to wind-shear effects, the position of the time-averaged centerline of the plumes may differ from the plume emission height. This mismatch can be an additional source of error if a Gaussian plume model (GPM) is used to interpret the measurement. In the case of the car transect measurements, a correct source estimate then requires an adjustment of the source height in the GPM.

Monitoring of Anthropogenic Sediment Plumes in the Clarion-Clipperton Zone, NE Equatorial Pacific Ocean

The abyssal seafloor in the Clarion-Clipperton Zone (CCZ) in the NE Pacific hosts the largest abundance of polymetallic nodules in the deep sea and is being targeted as an area for potential deep-sea mining. During nodule mining, seafloor sediment will be brought into suspension by mining equipment, resulting in the formation of sediment plumes, which will affect benthic and pelagic life not naturally adapted to any major sediment transport and deposition events. To improve our understanding of sediment plume dispersion and to support the development of plume dispersion models in this specific deep-sea area, we conducted a small-scale, 12-hour disturbance experiment in the German exploration contract area in the CCZ using a chain dredge. Sediment plume dispersion and deposition was monitored using an array of optical and acoustic turbidity sensors and current meters placed on platforms on the seafloor, and by visual inspection of the seafloor before and after dredge deployment. We found that seafloor imagery could be used to qualitatively visualise the redeposited sediment up to a distance of 100 m from the source, and that sensors recording optical and acoustic backscatter are sensitive and adequate tools to monitor the horizontal and vertical dispersion of the generated sediment plume. Optical backscatter signals could be converted into absolute mass concentration of suspended sediment to provide quantitative data on sediment dispersion. Vertical profiles of acoustic backscatter recorded by current profilers provided qualitative insight into the vertical extent of the sediment plume. Our monitoring setup proved to be very useful for the monitoring of this small-scale experiment and can be seen as an exemplary strategy for monitoring studies of future, upscaled mining trials. We recommend that such larger trials include the use of AUVs for repeated seafloor imaging and water column plume mapping (optical and acoustical), as well as the use of in-situ particle size sensors and/or particle cameras to better constrain the effect of suspended particle aggregation on optical and acoustic backscatter signals.

Implications of Local Scale Meteorological Data on Radioactive Plume Dispersion and Dose Delivery for a Hypothetical Severe Accident at PARR-1

Implications of Local Scale Meteorological Data on Radioactive Plume Dispersion and Dose Delivery for a Hypothetical Severe Accident at PARR-1

Coupling effects of tide and salting-out on perfluorooctane sulfonate (PFOS) transport and adsorption in a coastal aquifer

The adsorption of perfluorooctane sulfonate (PFOS) on sediments is thought to be enhanced by the ‘salting-out effect’ (SOE), which reduces contaminant solubility as water salinity increases. The process of salting-out has been observed for PFOS in surface estuaries and likely operates in ‘subterranean estuaries’, where tide-induced groundwater circulation creates a dynamic saltwater-freshwater mixing zone in the aquifer adjacent to the ocean. The presence of this dynamic interface between dense seawater and fresh groundwater modifies the flow path of land-derived organic contaminants. However, it is unclear how SOE combined with tidal forcing of salt water, affects the transport and fate of these contaminants in a subterranean estuary. Numerical studies of groundwater dynamics in a coastal aquifer are carried out using a modified version of SUTRA to investigate the behavior of PFOS, as it moves through an aquifer-ocean interface. Three adsorption scenarios are investigated: no adsorption and linear adsorption with a constant coefficient (Kd) and a salinity-dependent Kd (due to SOE). Without adsorption, point-injected PFOS moves and spreads as a plume around the margin of the tide-induced upper saline plume (USP). This is in agreement with previous studies showing that a contaminant plume follows the freshwater discharge path and exits the aquifer around the USP in the intertidal zone. The increase of tidal amplitude enlarges the USP, forcing the discharge points of freshwater and PFOS seaward. In the case of a constant Kd, PFOS concentration decreases in the groundwater as expected with an increase of PFOS residence time in the aquifer. The spatial distribution of the contaminant plume is similar to that of the ‘no adsorption’ case. In the case with the SOE, which enhances the solute adsorption in the saltwater zone, PFOS tends to be intercepted by the USP, concentrated at its center, and subsequently discharged with the tide-induced saltwater circulation. SOE reduces both peak PFOS discharge rate and plume dispersion. In addition, the PFOS flow path moves upward and the PFOS discharges above the USP. The findings highlight the potential importance of investigating the SOE of organic contaminants for benthic organisms when considering their transport and fate in tidally influenced coastal aquifers.

Mercury Isotope Variations in Lake Sediment Cores in Response to Direct Mercury Emissions from Non-Ferrous Metal Smelters and Legacy Mercury Remobilization.

Nature archives record atmospheric mercury (Hg) depositions from directly emitted Hg and re-emitted legacy Hg. Tracing the legacy versus newly deposited Hg is still, however, challenging. Here, we measured Hg isotope compositions in three dated sediment cores at different distances from the Flin Flon smelter, the largest Canadian Hg sources to the atmosphere during the 1930s-2000s. During the smelter's operative period, Hg isotope compositions showed limited variations in the near-field lake (<10 km) sediments but were rather variable in middle- (20-75 km) and far-field lake (∼800 km) sediments. Only the post-2000 sediments in middle/far-field lakes showed significantly negative Hg isotope shifts, while sediments from the 1970s-1990s had Hg isotope values resembling those of near-field lake post-1930 sediments. We suggest that the smelter's peak Hg emissions during the 1970s-1990s, which coincided with the deployment of a super stack in the mid-1970s, largely increased the long-range dispersion of smelter plumes. For the top post-2000 sediments, the fugitive dust from ore tailings and terrestrial legacy Hg re-emissions dominated Hg deposition in near-field lakes and middle/far-field lakes, respectively. Our study demonstrates that legacy Hg remobilization now exports substantial amounts of Hg to ecosystems, highlighting the need for aggressive remediation measures of Hg-contaminated sites.

An emergency response model for the formation and dispersion of plumes originating from major fires (BUOYANT v4.20)

Abstract. A mathematical model called BUOYANT has previously been developed for the evaluation of the dispersion of positively buoyant plumes originating from major warehouse fires. The model addresses the variations of the cross-plume integrated properties (i.e., the average properties along a trajectory) of a rising plume in a vertically varying atmosphere and the atmospheric dispersion after the plume rise regime. We have described in this article an extension of the BUOYANT model to include a detailed treatment of the early evolution of the fire plumes before the plume rise and atmospheric dispersion regimes. The input and output of the new module consist of selected characteristics of forest or pool fires and the properties of a source term for the plume rise module, respectively. The main structure of this source term module is based on the differential equations for low-momentum releases of buoyant material, which govern the evolution of the plume radius, as well as velocity and density differences. The source term module is also partially based on various experimental results on fire plumes. We have evaluated the refined BUOYANT model by comparing the model predictions against the experimental field-scale data from the Prescribed Fire Combustion and Atmospheric Dynamics Research Experiment, RxCADRE. The predicted concentrations of CO2 agreed fairly well with the aircraft measurements conducted in the RxCADRE campaign. We have also compiled an operational version of the model. The operational model can be used for emergency contingency planning and the training of emergency personnel in case of major forest and pool fires.

Dispersion of Benthic Plumes in Deep-Sea Mining: What Lessons Can Be Learned From Dredging?

Over the past decade, deep-sea mining (DSM) has received renewed interest due to scarcity of raw materials. Deep-sea mining has been spurred by the need for critical resources to support growing populations, urbanization, high-tech applications and the development of a green energy economy. Nevertheless, an improved understanding of how mining activities will affect the deep-sea environment is required to obtain more accurate assessment of the potential environmental impact. In that regard, the sediment plumes that are generated by the mining activity have received the highest concern, as these plumes might travel for several kilometers distance from the mining activity. Various plume sources are identified, of which the most profound are those generated by the excavation and collection process of the seafloor mining tool and the discharge flow to be released from the surface operation vessel after initial dewatering of the ore. In this review, we explore the physical processes that govern plume dispersion phenomena (focusing in the main on benthic plumes), discuss the state of the art in plume dispersion analysis and highlight what lessons can be learned from shallow water applications, such as dredging, to better predict and reduce the spread and impact of deep-sea mining plumes.