Fate Of Particles Research Articles

Creating respiratory pathogen-free environments in healthcare and nursing-care settings: a comprehensive review.

Hospital- and nursing-care-acquired infections are a growing problem worldwide, especially during epidemics, posing a significant threat to older adults in geriatric settings. Intense research during the COVID-19 pandemic highlighted the prominent role of aerosol transmission of pathogens. Aerosol particles can easily adsorb different airborne pathogens, carrying them for a long time. Understanding the dynamics of airborne pathogen transmission is essential for controlling the spread of many well-known pathogens, like the influenza virus, and emerging ones like SARS-CoV-2. Particles smaller than 50 to 100µm remain airborne and significantly contribute to pathogen transmission. This review explores the journey of pathogen-carrying particles from formation in the airways, through airborne travel, to deposition in the lungs. The physicochemical properties of emitted particles depend on health status and emission modes, such as breathing, speaking, singing, coughing, sneezing, playing wind instruments, and medical interventions. After emission, sedimentation and evaporation primarily determine particle fate. Lung deposition of inhaled aerosol particles can be studied through in vivo, in vitro, or in silico methods. We discuss several numerical lung models, such as the Human Respiratory Tract Model, the LUng Dose Evaluation Program software (LUDEP), the Stochastic Lung Model, and the Computational Fluid Dynamics (CFD) techniques, and real-time or post-evaluation methods for detecting and characterizing these particles. Various air purification methods, particularly filtration, are reviewed for their effectiveness in healthcare settings. In the discussion, we analyze how this knowledge can help create environments with reduced PM2.5 and pathogen levels, enhancing safety in healthcare and nursing-care settings. This is particularly crucial for protecting older adults, who are more vulnerable to infections due to weaker immune systems and the higher prevalence of chronic conditions. By implementing effective airborne pathogen control measures, we can significantly improve health outcomes in geriatric settings.

A Digital Twin of the Trondheim Fjord for Environmental Monitoring—A Pilot Case

Digital Twins of the Ocean (DTO) are a rapidly emerging topic that has attracted significant interest from scientists in recent years. The initiative, strongly driven by the EU, aims to create a digital replica of the ocean to better understand and manage marine environments. The Iliad project, funded under the EU Green Deal call, is developing a framework to support multiple interoperable DTO using a federated systems-of-systems approach across various fields of applications and ocean areas, called pilots. This paper presents the results of a Water Quality DTO pilot located in the Trondheim fjord in Norway. This paper details the building blocks of DTO, specific to this environmental monitoring pilot. A crucial aspect of any DTO is data, which can be sourced internally, externally, or through a hybrid approach utilizing both. To realistically twin ocean processes, the Water Quality pilot acquires data from both surface and benthic observatories, as well as from mobile sensor platforms for on-demand data collection. Data ingested into an InfluxDB are made available to users via an API or an interface for interacting with the DTO and setting up alerts or events to support ’what-if’ scenarios. Grafana, an interactive visualization application, is used to visualize and interact with not only time-series data but also more complex data such as video streams, maps, and embedded applications. An additional visualization approach leverages game technology based on Unity and Cesium, utilizing their advanced rendering capabilities and physical computations to integrate and dynamically render real-time data from the pilot and diverse sources. This paper includes two case studies that illustrate the use of particle sensors to detect microplastics and monitor algae blooms in the fjord. Numerical models for particle fate and transport, OpenDrift and DREAM, are used to forecast the evolution of these events, simulating the distribution of observed plankton and microplastics during the forecasting period.

Lagrangian flow networks for passive dispersal: Tracers versus finite-size particles.

The transport and distribution of organisms such as larvae, seeds, or litter in the ocean as well as particles in industrial flows is often approximated by a transport of tracer particles. We present a theoretical investigation to check the accuracy of this approximation by studying the transport of inertial particles between different islands embedded in an open hydrodynamic flow aiming at the construction of a Lagrangian flow network reflecting the connectivity between the islands. To this end, we formulate a two-dimensional kinematic flow field which allows the placement of an arbitrary number of islands at arbitrary locations in a flow of prescribed direction. To account for the mixing in the flow, we include a von Kármán vortex street in the wake of each island. We demonstrate that the transport probabilities of inertial particles making up the links of the Lagrangian flow network essentially depend on the properties of the particles, i.e., their Stokes number, the properties of the flow, and the geometry of the setup of the islands. We find a strong segregation between aerosols and bubbles. Upon comparing the mobility of inertial particles to that of tracers or neutrally buoyant particles, it becomes apparent that the tracer approximation may not always accurately predict the probability of movement. This can lead to inconsistent forecasts regarding the fate of marine organisms, seeds, litter, or particles in industrial flows.

Airflow and aerosol transport in the hospital isolation zone based on dynamic scenarios

To contain the leakage of viral aerosols, buffer rooms are usually provided in front of isolation wards. However, dynamic events of door movement and healthcare worker (HCW) walking will result in highly concentrated aerosols intruding into the buffer room from the ward, challenging the control of virus transmission risk. In this work, airflow exchange and bioaerosol particle transport between the negative-pressure isolation ward and the buffer room under dynamic scenarios were studied by transient computational fluid mechanics (CFD) simulation, thereby the fate of particles was divided into invasion stage and decay stage. The effects of ventilation pattern and HCW location on the concentration level and attenuation trend of particles were quantitatively analyzed. The results showed that increasing the HCW walking distance could increase the peak particle concentration within the buffer room by 4.5 % during the invasion stage. The effect of the buffer room ventilation layout on air exchange and particle transport was more pronounced than the HCW stay position. In the decay stage, the two more effective ventilation layouts could decrease the complete clearance time of particles and the particle concentration in the breathing zone by 31 % and 42 %, respectively. To reduce the infection risk, bioaerosol levels need to be reduced both in the buffer room and in the HCW breathing zone.

Micro- and Nano-Plastics Induced Release of Protein-Enriched Microbial Exopolymeric Substances (EPSs) in Marine Environments

Plastics are produced, consumed, and disposed of worldwide, with more than eight million tons of plastic litter entering the ocean each year. Plastic litter accumulates in marine and terrestrial environments through a variety of pathways. Large plastic debris can be broken down into micro- and nano-plastic particles through physical/mechanical mechanisms and biologically or chemically mediated degradation. Their toxicity to aquatic organisms includes the scavenging of pollutant compounds and the production of reactive oxygen species (ROS). Higher levels of ROS cause oxidative damages to microalgae and bacteria; this triggers the release of large amounts of exopolymeric substances (EPSs) with distinct molecular characteristics. This review will address what is known about the molecular mechanisms phytoplankton and bacteria use to regulate the fate and transport of plastic particles and identify the knowledge gaps, which should be considered in future research. In particular, the microbial communities react to plastic pollution through the production of EPSs that can reduce the plastic impacts via marine plastic snow (MPS) formation, allowing plastics to settle into sediments and facilitating their removal from the water column to lessen the plastic burden to ecosystems.

Interfacial interactions of nanoscale zero-valent iron particles with clay minerals in the aquatic environments: Experimental and theoretical calculation study

The environmental transport and fate of nanoscale zero-valent iron particles (nZVI) in soil and groundwater can be altered by their hetero-aggregation with clay mineral particles (CMP). This study examines the interactions between bare or carboxymethyl cellulose (CMC)-coated nZVI with typical CMP, specifically kaolinite and montmorillonite. Methods include co-settling experiments, aggregation kinetic studies, electron microscopy, Derjaguin–Landau–Verwey–Overbeek (DLVO) and extended DLVO (EDLVO) energy analysis, and density functional theory calculations, focusing on the pH dependency of these interactions. The EDLVO theory effectively described the interactions between nZVI and CMP in aquatic environments. Under acidic conditions (pH 3.5), the interfacial interaction between bare nZVI and kaolinite is regulated by van der Waals forces, while complexation, van der Waals forces, and electrostatic attraction govern the interaction of bare nZVI with montmorillonite, primarily depositing on the SiO face. In contrast, the positively charged AlO face and edge of CMP are the main deposition sites for CMC-coated nZVI through hydrogen bonding, van der Waals forces, and electrostatic attraction. At neutral (pH 6.5) and alkaline (pH 9.5) conditions, both bare and CMC-coated nZVI predominantly attach to the AlO face and edge, facilitated by complexation or hydrogen bonding, alongside van der Waals forces. The attachment of CMC-coated nZVI to CMP surfaces shows reversible aggregation or deposition due to the steric repulsion from the CMC coating. These findings hold significant implications for the environmental applications and risk of nZVI.

Production and characterisation of environmentally relevant microplastic test materials derived from agricultural plastics

Soil environments across the globe, particularly in agricultural settings, have now been shown to be contaminated with microplastics. Agricultural plastics – such as mulching films – are used in close or direct contact with soils and there is growing evidence demonstrating that they represent a potential source of microplastics. There is a demand to undertake fate and effects studies to understand the behaviour and potential long-term ecological risks of this contamination. Yet, there is a lack of test materials available for this purpose. This study describes the manufacture and characterisation of five large (1–40 kg) batches of microplastic test materials derived from agricultural mulching films. Batches were produced from either polyethylene-based conventional mulching films or starch-polybutadiene adipate terephthalate blend mulching films that are certified biodegradable in soil. Challenges encountered and overcome during the micronisation process provide valuable insights into the future of microplastic test material generation from these material types. This includes difficulties in micronising virgin polyethylene film materials. All five batches were subjected to a thorough physical and chemical characterisation - both of the original virgin films and the subsequent microplastic particles generated - including a screening for the presence of chemical additives. This is a critical step to provide essential information for interpreting particle fate or effects in scientific testing. Trade-offs between obtaining preferred particle typologies and time and cost constraints are elucidated. Several recommendations emerging from the experiences gained in this study are put forward to advance the research field towards greater harmonisation and utilisation of environmentally relevant test materials.

Bisphenol A sorption on commercial polyvinyl chloride microplastics: Effects of UV-aging, biofilm colonization and additives on plastic behaviour in the environment.

Chemical additives are important components in commercial microplastics and their leaching behaviour has been widely studied. However, little is known about the potential effect of additives on the adsorption/desorption behaviour of pollutants on microplastics and their subsequent role as vectors for pollutant transport in the environment. In this study, two types of commercial polyvinyl chloride (PVC1 and PVC2) microplastics were aged by UV irradiation and biotic modification via biofilm colonization to investigate the adsorption and desorption behaviour of bisphenol A (BPA). Surface cracks and new functional groups (e.g., O–H) were found on PVC1 after UV irradiation, which increased available adsorption sites and enhanced H‒bonding interaction, resulting in an adsorption capacity increase from 1.28 μg/L to 1.85 μg/L. However, the adsorption and desorption capacity not showed significant changes for PVC2, which might be related to the few characteristic changes after UV aging with the protection of light stabilizers and antioxidants. The adsorption capacity ranged from 1.28 μg/L to 2.06 μg/L for PVC1 and PVC2 microplastics, and increased to 1.62 μg/L—2.95 μg/L after colonization by biofilms. The increased adsorption ability might be related to the N–H functional group, amide groups generated by microorganisms enhancing the affinity for BPA. The opposite effect was observed for desorption. Plasticizers can be metabolized during biofilm formation processes and might play an important role in microorganism colonization. In addition, antioxidants and UV stabilizers might also indirectly influence the colonization of microorganisms’ on microplastics by controlling the degree to which PVC microplastics age under UV. The amount of biomass loading on the microplastics would further alter the adsorption/desorption behaviour of contaminants. This study provides important new insights into the evaluation of the fate of plastic particles in natural environments.

Transport and retention of sinking microplastics in a well-mixed estuary

Estuaries have been shown to be potential hotspots of microplastic accumulation, but the hydrodynamic conditions and particle properties that control this process need further investigation. We have designed a series of numerical particle-tracking experiments to examine the sensitivity of retention in estuaries to particle size, particle density and varying tides and freshwater flow. At the end of the simulation, over 90 % of sinking particles are retained in the estuary, and the retention rate is further increased by high river runoff. In contrast, increased river discharge increases the number of marginally-buoyant (i.e. density close to estuarine water) particles that escape the estuary. Larger particle size tends to limit the downstream transport of sinking particles but can facilitate the transport of marginally-buoyant particles. Tidal asymmetry, vertical turbulent mixing and the vertical structure of the subtidal circulation are proposed as the underlying mechanisms controlling the fate of particles.

On Innermost Stable Spherical Orbits near a Rotating Black Hole: A Numerical Study of the Particle Motion near the Plunging Region

According to general relativity, astrophysical black holes are described by a small number of parameters. Apart from the mass of the black hole (M), among the most interesting characteristics is the spin (a), which determines the degree of rotation, i.e., the angular momentum of the black hole. The latter is observationally constrained by the spectral and timing properties of the radiation signal emerging from an accretion disk of matter orbiting near the event horizon. In the case of the planar (standard, equatorial) accretion disk, this is the location of the innermost stable circular orbit that determines the observable radiation characteristics and allows us to measure the spin. In this paper, we discuss a more general case of the innermost stable spherical orbits (ISSOs) extending above and below the equatorial plane. To this end, we study the nonequatorial geodesic motion of particles following inclined, spherical, relativistically precessing trajectories with the aim of exploring the boundary between the regions of stable (energetically bound) and escaping (energetically unbound) motion. The concept of the radius of the ISSO should play a role in determining the inner rim of a tilted or geometrically thick accretion flow. We demonstrate that the region of inclined bound orbits has a complicated structure due to enhanced precession near the inner rim. We also explore the fate of particles launched below the radius of the marginally bound spherical orbit: these may either plunge into the event horizon or escape to radial infinity.

Synthesis and stabilities of Fe, Ni and Zn oxide incorporated colloidal TiO2

Owing to the unique physical and chemical characteristics of nanoparticles (NPs), their use in the manufacturing of commercial products is on the rise. The future will see an increasing quantity of NPs being discharged into our surroundings. This is precisely why it is important to understand their stability under changing conditions. This research examined the role of added Fe (III), Ni (II) and Zn (II) on the formation and stabilities of aqueous colloids of TiO2 particles. To the best of our knowledge, this is the first attempt to investigate the stability of lab synthesized composite NPs. The study confirmed that both the stability and environmental fate of metal oxide and mixed metal oxide NPs depends on the composition of aqueous environment. This can add more to the general understanding of NPs while paving way for exploring the stability and environmental fate of various mixed metal oxide/composites NPs as previous studies explored only commercially prepared plain NPs. TiO2 and TiO2-Fe2O3, TiO2-NiO, and TiO2-ZnO were synthesized following reported methods. Different characterization techniques including transmission electron microscope (TEM), x-rays diffraction (XRD), energy dispersive X-ray (EDX) analysis, and dynamic light scattering (DLS) were used to confirm the surface morphology, phase, elemental composition, and hydrodynamic (Dh) size of synthesized TiO2 particles. As-synthesized TiO2 and its various forms (TiO2-Fe2O3, TiO2-NiO, and TiO2-ZnO) showed rapid aggregation behavior in solutions, which is a sign of less or no threat to human health and the environment. Among the synthesized composites, TiO2-Fe2O3 showed the highest stability across all the methods utilized in this research. For all the approaches employed in dispersing aggregates of TiO2 NPs and their composites in solution, homogenization method displayed the highest efficiency. Moreover, the addition of an electrolyte i.e., KCl into the particle suspensions has affected the ionic strength of these suspensions resulting in an increased aggregation due to the shifting of ions-particles equilibrium. Thus, the formation of composites on TiO2 can govern both the stability and environmental fate of TiO2 particles under various aqueous environments.

Effect of water-soluble polymers on the transport of functional group-modified polystyrene nanoplastics in goethite-coated saturated porous media

The research on the impact of water-soluble polymers (WSPs) on the migration and fate of plastic particles is extremely limited. This article explored the effects of polyacrylic acid (PAA, a common WSP) and physicochemical factors on the transport of polystyrene nanoparticles (PSNPs-NH2/COOH) with different functional groups in QS (quartz sand) and FOS (goethite-modified quartz sand, simulates mineral colloids). Research has shown that PAA can selectively adsorb onto the surface of PSNPs-NH2, forming ecological corona heterogeneous aggregates. This process increased the spatial hindrance and elastic repulsion, resulting in the recovery of PSNPs-NH2 always exceeding that of PSNPs-COOH. Overall, PAA can hinder the migration of PSNPs in QS but can promote their migration in FOS. When multivalent cations coexist with PAA, the transport of PSNPs in the media is primarily affected by cation bridging and CH-cation-π interaction. The presence of oxyanions and PAA prevents PSNPs from following the Hofmeister rule and promotes their migration (PO43-: 82.34 ± 0.16% to 94.63 ± 2.82%>SO42-: 81.38 ± 2.73% to 91.15 ± 0.93%>NO3-: 55.85 ± 0.70%−87.16 ± 3.80%). The findings of this study contribute significantly to a better understanding of the migration of WSPs and group-modified NPs in complex saturated porous media.

Fate and effects of microplastic particles in a periphyton-grazer system

In the aquatic environment, microplastic particles (MP) can accumulate in microbial communities that cover submerged substrata, i.e. in periphyton. Despite periphyton being the essential food source for grazers in the benthic zones, MP transfer from periphyton to benthic biota and its ecotoxicological consequences are unknown. Therefore, in this study, we investigated the effects of 1) MP on embryonal development of freshwater gastropod Physa acuta embryos, 2) MP on adult Physa acuta individuals through dietary exposure and 3) on the MP surface properties. Embryonal development tests were carried out with spherical polyethylene MP in the size of 1–4 μm (MP). Over a period of 28 days, embryonal development and hatching rate were calculated. In the feeding experiments, periphyton was grown in the presence and absence of MP and was then offered to the adult Physa acuta for 42–152 h. The snails readily ingested and subsequently egested MP, together with the periphyton as shown by MP quantification in periphyton, snail soft body tissue and feces. No selective feeding behavior upon MP exposure was detected. The ingestion of MP had no effect on mortality, feeding and defecation rate. Yet, the reproductive output of snails, measured as the number of egg clutches and numbers of eggs per clutch, decreased after the ingestion of MPs, while the hatching success of snail embryos those parents were exposed remained unaffected. In contrast, hatching rate of snail embryos was significantly reduced upon direct MP exposure. MP optical properties were changed upon the incorporation into the periphyton and the passage through the digestive tract. Our results indicate that MP incorporated in periphyton are bioavailable to aquatic grazers, facilitating the introduction of MP into the food chain and having direct adverse effects on the grazers’ reproductive fitness.

Wave‐Driven Vertical Sorting of Density‐Varying Particles

AbstractIt has been recognized that the vertical sorting of polydispersed sand grains via the “Brazil Nut effect” can lead to inverse grading (upward coarsening) in the surface layer of a sand bed. However, the addition of nonnative particles not inherently observed on the beach, characterized by different densities and sizes, may complicate the vertical sorting processes and the fate of the nonnative particles. For example, olivine particles, which may be released on natural sandy beaches to facilitate carbon dioxide capture via weathering from wave action, have a density about 25% larger than the typical native sands. An Eulerian‐Lagrangian model, which couples Computational Fluid Dynamics for the fluid phase and Discrete Element Method for the particle phase was utilized to investigate how the so‐called “Reverse Brazil Nut effect” due to the larger density of nonnative (olivine) particles may be counteracted by the so‐called “Brazil Nut effect” for a range of nonnative particle sizes. Numerical simulations showed that the higher‐density nonnative particles tended to sink into the sand bed consistent with the “Reverse Brazil Nut effect”; however, the vertical sorting structure of native sand, driven by the “Brazil Nut effect,” also was a controlling factor determining the fate of nonnative particles. To maintain the presence of the nonnative (olivine) particles in the active layer of sediment transport, the higher‐density nonnative particle size must be larger than the mean native sand size found at the bottom of the active layer.

On the Fate of Slow Boulders Ejected after DART Impact on Dimorphos

On 2022 September 26 23:14 UT, the NASA Double Asteroid Redirection Test spacecraft successfully impacted Dimorphos, the secondary component of the binary (65803) Didymos system, demonstrating asteroid orbit deflection for the first time. A large amount of debris, consisting of a wide size–frequency distribution of particulates (from micron-sized dust to meter-sized boulders), was released, and a long-lasting tail has been observed over more than 9 months since impact. An important fraction of the ejecta mass has been ejected as individual meter-sized boulders, as have been found in images obtained by the Light Italian CubeSat for Imaging of Asteroid (LICIACube), as well as from the Hubble Space Telescope (HST). While the boulders observed by LICIACube had projected speeds of several tens of m s–1, those seen by the HST were about 100 times slower. In this paper, we analyze the long-term orbital evolution of those slow boulders using different dynamical codes, providing constraints on the fate of such large particles, and giving insight on the possibility of observing some of those boulders that might remain in orbit at the time of the ESA/Hera mission arrival to the binary system in late 2026.

Self-Assembly of Heterogeneous Ferritin Nanocages for Tumor Uptake and Penetration.

Well-defined nanostructures are crucial for precisely understanding nano-bio interactions. However, nanoparticles (NPs) fabricated through conventional synthesis approaches often lack poor controllability and reproducibility. Herein, a synthetic biology-based strategy is introduced to fabricate uniformly reproducible protein-based NPs, achieving precise control over heterogeneous components of the NPs. Specifically, a ferritin assembly toolbox system is developed that enables intracellular assembly of ferritin subunits/variants in Escherichia coli. Using this strategy, a proof-of-concept study is provided to explore the interplay between ligand density of NPs and their tumor targets/penetration. Various ferritin hybrid nanocages (FHn) containing human ferritin heavy chains (FH) and light chains are accurately assembled, leveraging their intrinsic binding with tumor cells and prolonged circulation time in blood, respectively. Further studies reveal that tumor cell uptake is FH density-dependent through active binding with transferrin receptor 1, whereas in vivo tumor accumulation and tissue penetration are found to be correlated to heterogeneous assembly of FHn and vascular permeability of tumors. Densities of 3.7FH/100nm2 on the nanoparticle surface exhibit the highest degree of tumor accumulation and penetration, particularly in tumors with high permeability compared to those with low permeability. This study underscores the significance of nanoparticle heterogeneity in determining particle fate in biological systems.

Quantifying the Chemical Composition and Real-Time Mass Loading of Nanoplastic Particles in the Atmosphere Using Aerosol Mass Spectrometry.

Plastic debris, including nanoplastic particles (NPPs), has emerged as an important global environmental issue due to its detrimental effects on human health, ecosystems, and climate. Atmospheric processes play an important role in the transportation and fate of plastic particles in the environment. In this study, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was employed to establish the first online approach for identification and quantification of airborne submicrometer polystyrene (PS) NPPs from laboratory-generated and ambient aerosols. The fragmentation ion C8H8+ is identified as the major tracer ion for PS nanoplastic particles, achieving an 1-h detection limit of 4.96 ng/m3. Ambient PS NPPs measured at an urban location in Texas are quantified to be 30 ± 20 ng/m3 by applying the AMS data with a constrained positive matrix factorization (PMF) method using the multilinear engine (ME-2). Careful analysis of ambient data reveals that atmospheric PS NPPs were enhanced as air mass passed through a waste incinerator plant, suggesting that incineration of waste may serve as a source of ambient NPPs. The online quantification of NPPs achieved through this study can significantly improve our understanding of the source, transport, fate, and climate effects of atmospheric NPPs to mitigate this emerging global environmental issue.

Lagrangian and Eulerian modelling of river plumes in the Great Barrier Reef system, Australia

In this paper, we describe methods to verify the adequacy and accuracy of Lagrangian particles from a Lagrangian model to reproduce the concentrations of a passive tracer from an Eulerian-model in river plumes. The modelling simulates plumes from two major rivers discharging in the Great Barrier Reef (GBR), Australia, under real-world scenarios. The study has been a part of a major project to aid in the protection of the GBR system from the impacts of extreme events and climate change. We employ the Regional Ocean Modelling System (ROMS) activated with its built-in Lagrangian model, and forced with wind fields from global models and recorded river volume discharges. The ROMS-Lagrangian model tracks the Lagrangian particles using the spatially interpolated velocities computed on the Eulerian ROMS three-dimensional (3D) grid. The Lagrangian particles are released in the river in proportion to the measured river volume flux. We apply a novel technique that exploits Voronoi polygon areas to convert Lagrangian particle separation into a concentration field. This facilitates comparison with the passive tracer concentrations driven by the Eulerian velocities computed on the ROMS 3D grid. We evaluate the fate of Lagrangian particles activated on a 4-km grid resolution with those of equivalent Eulerian tracer concentrations. For validation, we compare the Lagrangian particles with the Eulerian passive tracer simulated using a higher model grid resolution of 500-m, and found that the computed Lagrangian particle concentrations showed similar overall patterns compared to the passive tracer concentrations from both the coarse 4-km, and high-resolution 500-m Eulerian models. The spatial extent of the particles was in better agreement with the coarse 4-km model than with the higher resolution 500-m model. The clustering of particles resulted in structures at finer scales than the Eulerian model, over the high particle density areas that compared well against observations. The Lagrangian particles are able to capture the general river plume patterns seen in the satellite MODIS images and the satellite derived Chlorophyll-a. We further compare the online ROMS model with an offline particle tracker, OceanPARCELS and determined the similarity of results from both online and offline methods. Overall, our study demonstrates the viability to use Lagrangian particles to reproduce the Eulerian tracer properties, which can be combined with particle properties include tracer age providing to enhance the guidance on the distribution and concentration of effluent from localised flooding river events.

Colloid Transport and Retention in Constricted Tube Pore Spaces With Diverse Geometries and Orientations

AbstractColloidal contaminants infiltrate and can be attached onto grain surfaces of soils and aquifers, where they may persist. In this study, Lagrangian particle tracking is used to investigate particle trajectories and attachment in pore and fracture spaces modeled as three‐dimensional constricted tubes with diverse geometries and orientations relative to gravity. A comprehensive force balance arising from hydrodynamic drag and lift, gravitational settling, Brownian motion, and attractive DLVO interactions is simulated. Results show that the collection efficiency η is primarily governed by the dimensionless settling number 𝑆, representing the relative dominance of gravitational over hydrodynamic forces experienced by the particles. High‐𝑆 scenarios have larger η and are more sensitive to pore orientation, while low‐𝑆 scenarios are more sensitive to pore geometry. For all scenarios but especially low‐S scenarios, the majority of colloid attachment occurs near pore extremities, where fluid velocities are low, such that mechanical remobilization of particles attached is improbable. In low‐𝑆 scenarios, particles may spread and become immobilized at greater distances from the contamination source owing to lower η, are harder to mechanically remobilize as they attach more disproportionately at pore extremities, and have trajectories more sensitive to minor forces, rendering their environmental fates complex. Characterizing the collection efficiency and deposition morphology for various pore space geometries and orientations is crucial in understanding particle fate and developing continuum‐scale models of colloid transport in real soils, where pore spaces are heterogeneous and advection paths are tortuous.

Study of electro-migration and capture of particles by a charged pendant droplet

To understand the particle scavenging mechanisms by charged droplets in air cleaning technologies, we investigate the phenomena of non-incorporation/non-attachment and return/rebound of airborne particles/clusters upon impacting charged droplets. Using high-speed imaging, the motion and fate of particles and clusters lifted from a surface and colliding with a stationary droplet suspended from an electrified needle are examined in detail. Aggregates of glass beads and carbon particles are employed to explore how material characteristics, such as hydrophobicity/hydrophilicity, conductivity, and dielectric constant, influence their capture by the droplet. Analysis of observed cluster trajectories along with numerical modelling has been carried out to provide insights into their charges and velocities. DC and AC electric field experiments unequivocally demonstrate that the Faradaic induction mechanism at both the ground and droplet surfaces causes the acquisition or reversal of particle charges. The migration of particles and clusters is predominantly governed by Coulombic force, not dielectrophoretic force (DEP). Hydrophobic carbon particle clusters with high conductivity exhibit increased rebound/non-incorporation from the droplet, whereas hydrophilic glass beads with low conductivity do not show significant rebound and readily integrate into the droplet. The study demonstrates that (i) particles deposited on surfaces suffer resuspension and (ii) the capture of particles striking a charged droplet surface may not take place universally but could have a strong dependence on the chemical and material nature of the particles. Although the study is based on aggregated clusters and not on individual particles, it opens up avenues for future research using smaller particles and droplet systems relevant to air-cleaning applications.