Particle Evaporation Research Articles

Towards utilization of iron powders for heating and power

In the present study, a novel and initiative approach towards a self-sustainable metal combustion burner called the “Metal Cyclonic Combustor (MC2)” is introduced. The results show that a self–sustained iron flame can be established inside the MC2 under normal air conditions (21% O2), and even at very low oxygen concentrations (∼ 10% O2) and for low overall equivalence ratios (∼ 0.2), without any assisting extra heat sources. However, the results demonstrate that a proper preheating level corresponding to the oxygen concentration can still guarantee flame stability even in lower oxygen concentrations as low as 5%. Moreover, it was shown that the iron particles’ temperature reduced significantly after switching to a combustion regime with low oxygen concentrations. This finding is significant in mitigating the partial evaporation of metal particles and circumventing nano-particle formation and related mass losses. Furthermore, some physicochemical complex phenomena and critical challenges (e.g. particle burning temperature, emissions, recyclability, etc.) that govern the optimal performance of metal combustion systems are recognized and discussed. It is believed that the results of this study may be of significant importance to lead us towards designing fully industrial and novel practical metal combustors/burners as a significant step forward towards developing high–energy density, zero-carbon, zero-emission (HEDZ) combustion-based systems needed for transition to carbon-free energy systems.

Isothermal evaporation of α-pinene secondary organic aerosol particles formed under low NOx and high NOx conditions

Abstract. Many recent secondary organic aerosol (SOA) studies mainly focus on biogenic SOA particles formed under low NOx conditions and thus are applicable to pristine environments with minor anthropogenic influence. Although interactions between biogenic volatile organic compounds and NOx are important in, for instance, suburban areas, there is still a lack of knowledge about the volatility and processes controlling the evaporation of biogenic SOA particles formed in the presence of high concentrations of NOx. Here we provide detailed insights into the isothermal evaporation of α-pinene SOA particles that were formed under low NOx and high NOx conditions to investigate the evaporation process and the evolution of particle composition during the evaporation in more detail. We coupled Filter Inlet for Gases and AEROsols-Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) measurements of the molecular composition and volatility of the particle phase with isothermal evaporation experiments conducted under a range of relative humidity (RH) conditions from low RH (<7 % RH) to high RH (80 % RH). Very similar changes were observed in particle volatility at any set RH during isothermal evaporation for the α-pinene SOA particles formed under low NOx and high NOx conditions. However, there were distinct differences in the initial composition of the two SOA types, possibly due to the influence of NOx on the RO2 chemistry during SOA formation. Such compositional differences consequently impacted the primary type of aqueous-phase processes in each type of SOA particle in the presence of particulate water.

Chemical species of cesium and iodine in condensed vaporized microparticles formed by melting nuclear fuel components with concrete materials.

In this study, we report chemical species of Cs and I in condensed vaporized particles (CVPs) produced by melting experiments using nuclear fuel components containing CsI with concrete. Analyses of CVPs by SEM with EDX showed the formation of many round particles containing Cs and I of diameters less than ∼20 μm. X-ray absorption near-edge-structure and SEM-EDX analyses showed two kinds of particles: one containing large amounts of Cs and I, suggesting the presence of CsI, and the other containing small amounts of Cs and I with large Si content. When CVSs were placed in contact with deionized water, most of the CsI from both particles was dissolved. In contrast, some fractions of Cs remained from the latter particles and possessed different chemical species from CsI. In addition, the remaining Cs was concomitantly present with Si, resembling chemical components in the highly radioactive cesium-rich microparticles (CsMPs) released by nuclear plant accidents into the surrounding environments. These results strongly suggest that Cs was incorporated in CVSs along with Si by melting nuclear fuel components to form sparingly-soluble CVMPs.

A skin-like nanostructured membrane for advanced wound dressing

An ideal wound dressing should include excellent physical property, comfortability, and protection. Critical properties, such as robust tensile stress, high water vapor transmission rate (WVTR), air permeability (AP), waterproofness, biocompatibility, and particle filtration efficiency (PFE) should be covered. However, previous research regarding wound dressings omitted some of these elements, leading to the fact that wound healing management was ineffective. Herein, inspired by human skin structure, we designed a skin-like wound dressing with a hydrophilic healing interlayer and a hydrophobic protective surface based on polyvinylidene fluoride. The prepared membrane not only possesses an excellent physical property, comfortability, and protective function but also can accelerate cell migration and the wound healing process. Particularly, the dressing demonstrates robust tensile stress of 25.9 MPa, a toughness of 12.2 MJ/m3, a typical WVTR over 17.4 kg/(m2·d), a high AP of 4.2 mL/s, a high PFE of 99.9%, excellent biocompatibility, and a more rapid scratch healing rate than the commercial product, Nexcare. The dressing is proven to be similar to human skin (i.e., tensile strength of 21.6 ± 8.4 MPa and failure strain of 54 ± 17%). We believe that the achieved scalable nanostructured membrane can make meritorious contributions to materials science and biomedical engineering.

Experimental study of moisture effects on spontaneous combustion of Baiyinhua lignite from individual particles to stockpile

Evaporation and condensation of moisture affect dramatically the spontaneous combustion of lignite with high moisture content at low temperatures. Moisture migration between the lignite and the external environment of coal stockpile encompasses the scales of individual particles and stockpile. The cyclic moisture evaporation/condensation test was applied to investigate moisture migration of individual lignite particles at different particle sizes and temperatures. The wire-mesh basket test was selected primarily to analyze the heating process and critical self-ignition temperature of lignite stockpile. Results of the cyclic moisture evaporation/condensation test reveal that the moisture content of re-saturated lignite is much lower than that of the original one. Moisture content versus time showed a tendency to overlap in repeated moisture evaporation processes, and so did the repeated moisture evaporation processes. Therefore, a model of moisture migration of individual particles was built to describe the repeated moisture evaporation and condensation processes. The time factor determines the speed of moisture evaporation and condensation of individual lignite particles, being inversely proportional to ambient temperature and proportional to particle size, respectively. In the wire-mesh basket test, the heating process of the lignite stockpile can be divided into four stages, but the influence of moisture was more pronounced in stage II. Critical self-ignition temperature is proportional to particle size and increases linearly with moisture content. According to Frank-Kamenetskii theory, an increase in either particle size or moisture content can restrain the tendency of spontaneous combustion of Baiyinhua lignite stockpile.

Nuclear level density and γ -ray strength function of Ni63

The nuclear level density (NLD) and $\gamma$-ray strength function ($\gamma$SF) of $^{63}\mathrm{Ni}$ have been investigated using the Oslo method. The extracted NLD is compared with previous measurements using particle evaporation and those found from neutron resonance spacing. The $\gamma$SF was found to feature a strong low energy enhancement that could be explained as M1 strength based on large scale shell model calculations. Comparison of $\gamma$SFs measured with the Oslo method for various $\mathrm{Ni}$ isotopes reveals systematic changes to the strength below $5$ MeV with increasing mass.

Comparison of the survival of different isolates of SARS-CoV-2 in evaporating aerosols

Numerous variants of SARS-CoV-2 with increased transmissibility have emerged over the course of the pandemic. Potential explanations for the increased transmissibility of these variants include increased shedding from infected individuals, increased environmental stability, and/or a lower infectious dose. Upon exhalation of a respiratory particle into the environment, water present in the particle is rapidly lost through evaporation, resulting in a decrease in particle size. The aim of the present study was to compare the losses of infectivity of different isolates of SARS-CoV-2 during the rapid evaporation of aerosol particles that occurs immediately post-generation to assess if there are differences suggestive of increased survival, and ultimately greater transmissibility, for more recent variants. Losses of infectivity of several isolates of SARS-CoV-2 suspended in viral culture media were assessed following aerosolization and evaporation in a flowing chamber. The results demonstrate that losses of infectivity measured post-evaporation were similar for three different isolates of SARS-CoV-2, including isolates from the more recent Delta and Omicron lineages. The average loss in infectivity across all three isolates was 61 ± 15% (−0.46 ± 0.17 log10 TCID50/L-air) at a relative humidity <30%. These results, together with those from several previous studies, suggest that it is unlikely that an increase in environmental stability contributes to the observed increases in transmissibility observed with more recent variants of SARS-CoV-2.

Global Modeling of Nebulae with Particle Growth, Drift, and Evaporation Fronts. II. The Influence of Porosity on Solids Evolution

Incremental particle growth in turbulent protoplanetary nebulae is limited by a combination of barriers that can slow or stall growth. Moreover, particles that grow massive enough to decouple from the gas are subject to inward radial drift, which could lead to the depletion of most disk solids before planetesimals can form. Compact particle growth is probably not realistic. Rather, it is more likely that grains grow as fractal aggregates, which may overcome this so-called radial drift barrier because they remain more coupled to the gas than compact particles of equal mass. We model fractal aggregate growth and compaction in a viscously evolving solar-like nebula for a range of turbulent intensities α t = 10−5–10−2. We do find that radial drift is less influential for porous aggregates over much of their growth phase; however, outside the water snowline fractal aggregates can grow to much larger masses with larger Stokes numbers more quickly than compact particles, leading to rapid inward radial drift. As a result, disk solids outside the snowline out to ∼10–20 au are depleted earlier than in compact growth models, but outside ∼20 au material is retained much longer because aggregate Stokes numbers there remain lower initially. Nevertheless, we conclude even fractal models will lose most disk solids without the intervention of some leapfrog planetesimal forming mechanism such as the streaming instability (SI), though conditions for the SI are generally never satisfied, except for a brief period at the snowline for α t = 10−5.

Global Modeling of Nebulae with Particle Growth, Drift, and Evaporation Fronts. III. Redistribution of Refractories and Volatiles

Formation of the first planetesimals remains an unsolved problem. Growth by sticking must initiate the process, but multiple studies have revealed a series of barriers that can slow or stall growth, most of them due to nebula turbulence. In a companion paper, we study the influence of these barriers on models of fractal aggregate and solid, compact particle growth in a viscously evolving solar-like nebula for a range of turbulent intensities α t = 10−5–10−2. Here, we examine how the disk composition in these same models changes with time. We find that advection and diffusion of small grains and vapor, and radial inward drift for larger compact particles and fractal aggregates, naturally lead to diverse outcomes for planetesimal composition. Larger particles can undergo substantial inward radial migration due to gas drag before being collisionally fragmented or partially evaporating at various temperatures. This leads to enhancement of the associated volatile in both vapor inside, and solids outside, their respective evaporation fronts, or snowlines. In cases of lower α t, we see narrow belts of volatile or supervolatile material develop in the outer nebula, which could be connected to the bands of pebbles seen by the Atacama Large Millimeter/submillimeter Array. Volatile bands, which migrate inwards as the disk cools, can persist over long timescales as their gas phase continues to advect or diffuse outward across its evaporation front. These belts could be sites where supervolatile-rich planetesimals form, such as the rare CO-rich and water-poor comets; giant planets formed just outside the H2O snowline may be enhanced in water.

Safety Assessment of Low-Flow Oxygenation Device: Quasi-Experimental Study.

The objective of this study was to verify the feasibility of using an Oxygenation Device with Reservoir and Positive End-Expiratory Pressure (ODRPEEP; DORPEEP in Spanish) and to analyze its safety with respect to mask leaks and carbon dioxide retention measured upon expiration. A quasi-experimental pilot study was designed with eight volunteers in two experiments to determine the degree of leaks from the device, according to the observation of water vapor particle diffusion, on the one hand, and of thermal images on the other. The results from this study showed that the mask from the DORPEEP© device at is tightest fit provided an adequate seal, although not fully airtight. In the thermal images and in the experiment with water vapor in our study, dispersions were mainly observed in the lower area in individuals with a beard. The DORPEEP© device was shown to have only slight leaks.

Influence of internal heat transfer on reactive force applied to powder particles in laser cladding

Formation of two-phase powder-gas flows is the key factor determining the quality of materials synthesized by laser cladding and similar laser processes. Currently, the influence of the processing laser beam on such flows is insufficiently studied. Recent experiments on high-speed imaging show that the laser beam can considerably accelerate and deviate the exposed powder particles. This phenomenon is commonly explained by the reactive force arising at laser evaporation of particles. It seems that the existing theoretical approaches considerably overestimate the reactive force because they ignore internal heat transfer in the particle. The aim of the present work is to analyze theoretically the combined conductive-convective heat transfer in the particle exposed to laser radiation and the related evaporation and formation of the resultant reactive force. Computational Fluid Dynamic (CFD) simulation has shown that the internal heat transfer can reduce the temperature gradient in the particle, thus considerably reducing the resultant reactive force in the typical conditions of laser cladding. The CFD indicates that in such conditions, the influence of convection on the reactive force is low. An analytic model of conductive heat transfer and evaporation of a spherical particle is developed. The CFD validates this model and indicates that the confidence interval of the estimated resultant reactive force is within 1%. This model can be useful for analyzing experimental data and simulation of gas-powder flows exposed to laser radiation.

Characterization of micron-sized particles in the focused laser beam during fiber laser keyhole welding

In this study, the self-mixing interferometry (SMI) method was used for in situ measuring the micron-sized particles characterization in the focused fiber laser beam (FFLB) during the fiber laser keyhole welding. The micron-sized particles in the FFLB have a diameter of 0.655–6.55 μm and a velocity of 1–90 m/s, and particles with a larger diameter exhibited higher velocities. The share of particles with a diameter of 0.655–2 μm and that of particles with a velocity of 1–10 m/s decreased with the laser power, and increase with the detection height. The number, diameter and percentage of particles with higher velocities increased with the laser power and decreased with the detection height. These trends were due to particle vaporization induced by laser in the FFLB. In situ measurements characterization of particles was found instrumental in adjusting the laser power and detection positions.

Early particle formation and evolution in iron-doped flames

In flame synthesis of nanoparticles, the temperature history experienced by the nascent particle aerosol defines the morphology, composition, and crystallinity of the resulting nanomaterial. Commonly, flame-synthesis processes are modeled with an isothermal approximation assuming that the particle temperature replicates that of the surrounding gas phase, avoiding inclusion of an additional internal coordinate in the population balance model, and thus reducing the computational cost. This simplification neglects the influence of matter- and energy-exchange as well as thermochemistry between the particle and reactive gas phase, impacting the particle temperature. In this work, we investigate the temperature history of the particles in incipient formation stages and their evolution in iron-doped flames, prototypical for many other transition-metal (oxide) synthesis systems. The temperature and relative volume-fraction distributions of early particles forming in H2/O2/Ar flames doped with iron pentacarbonyl were determined for the first time, based on spectrally and spatially resolved flame emission measurements and pyrometric analysis of the continuum emission emanating from the nascent particle aerosol. The nascent particle temperature was found to be several hundred degrees above the gas-phase temperature for all physically reasonable assumptions concerning particle composition and emission efficiency. Early particles volume fraction rises sharply shortly after the decomposition of iron pentacarbonyl and decreases steeply in the flame front, in excellent agreement with previous particle-mass spectrometry/quartz-crystal microbalance measurements. By modeling the evaporation process of isothermal iron particles, we show that vanishing of particles in the flame front cannot be explained by evaporation of particles that are in thermal equilibrium with the gas phase. A single-particle Monte-Carlo simulation based on a simple model comprising Fe-monomer condensation, concurrent with oxidation, reduction, etching, and evaporation occurring at the particle surface, captures both the flame structure with respect to early particle formation and their excess temperature compared to the gas phase.

Mineral snowflakes on exoplanets and brown dwarfs

Context. Brown dwarfs and exoplanets provide unique atmospheric regimes that hold information about their formation routes and evolutionary states. Cloud particles form through nucleation, condensation, evaporation, and collisions, which affect the distribution of cloud particles in size and throughout these atmospheres. Cloud modelling plays a decisive role in understanding these regimes. Aims. Modelling mineral cloud particle formation in the atmospheres of brown dwarfs and exoplanets is a key element in preparing for missions and instruments like CRIRES+, JWST, and ARIEL, as well as possible polarimetry missions like PolStar. The aim is to support the increasingly detailed observations that demand greater understanding of the microphysical cloud processes. Methods. We extend our kinetic cloud formation model that treats nucleation, condensation, evaporation, and settling of mixed material cloud particles to consistently model cloud particle-particle collisions. The new hybrid code Hybrid moments (Ls) and Size (HyLandS) is then applied to a grid of Drift-Phoenix (Tgas, pgas) profiles. Effective medium theory and Mie theory are used to investigate the optical properties. Results. Turbulence proves to be the main driving process of particle-particle collisions, with collisions becoming the dominant process in the lower atmosphere (p &gt; 10−4 bar) at the cloud base. Particle-particle collisions produce one of three outcomes for brown dwarf and gas-giant atmospheres: fragmenting atmospheres (log10(g[cms−2])=3.0) coagulating atmospheres (log10(g)=5.0), Teff ≤1800K) or condensational growth dominated atmospheres (log10(g) = 5.0, Teff &gt; 1800 K). Cloud particle opacity slope at optical wavelengths (Hubble) is increased with fragmentation, as are the silicate features at JWST NIRSpec, JWST MIRI, and ARIEL AIRS wavelengths. Conclusions. The hybrid moment-bin method HyLandS demonstrates the feasibility of combining a moment and a bin method for cloud modelling, whilst assuring element conservation. It provides a powerful and fast tool for capturing general trends of particle collisions, consistently with other microphysical growth processes. Collisions are an important process in exoplanet and brown dwarf atmospheres, but cannot be assumed to be hit-and-stick only. The spectral effects of cloud particle collisions in both optical and mid-infrared wavelengths complicate inferences of cloud particle size and material composition from observational data.

Analysis of non-ionized substance losses in experiments on plasma mass separation

Plasma mass separation requires a lot of diagnostic techniques that not only demonstrate the separation effect but also show the efficiency of the process. During the test experiments, plasma flux to be separated may contain neutral particles that avoid the separation process due to their insensitivity to electromagnetic field. We present the diagnostics of the lost substance in experiments on plasma mass separation. The obtained data of the diagnostics helps determine the law of particle evaporation from the plasma source. We show that neutral flux is unable to distort the result of separation diagnostics. The presented approach can be used in experiments aimed at enhancing the separation effect and achieving target productivity for industry applications.

Optimization of molecular beam epitaxial film thickness uniformity using Monte Carlo simulations and an artificial neural network.

The thickness uniformity of the molecular beam epitaxial film is one of the most important factors affecting the quality of the film, and it is mainly influenced by the angular distribution of the molecular source, which is mainly determined by the inner wall shape of the crucible. In this paper, an optimization method based on particle swarm optimization, Monte Carlo simulations, and an artificial neural network is proposed, aiming at optimizing the epitaxial film uniformity in the molecular beam epitaxy process. The optimum angular distribution of an effusion source is obtained by using the method of particle swarm optimization for a given geometric configuration. The Monte Carlo method is used to simulate the particle evaporation process to obtain the relationship between the shape parameters of the crucible inner wall and the particle angular distribution. The optimum crucible shape parameters are subsequently obtained under a particular apparatus geometric configuration by using the artificial neural network according to the above relationship and the desired optimum angular distribution. Finally, the optimized results are compared by experiments.

Core-collapse, evaporation, and tidal effects: the life story of a self-interacting dark matter subhalo

ABSTRACT Self-interacting dark matter (SIDM) cosmologies admit an enormous diversity of dark matter (DM) halo density profiles, from low-density cores to high-density core-collapsed cusps. The possibility of the growth of high central density in low-mass haloes, accelerated if haloes are subhaloes of larger systems, has intriguing consequences for small-halo searches with substructure lensing. However, following the evolution of ${\lesssim}10^8 \, \mathrm{M}_\odot$ subhaloes in lens-mass systems (${\sim}10^{13}\, \mathrm{M}_\odot$) is computationally expensive with traditional N-body simulations. In this work, we develop a new hybrid semi-analytical + N-body method to study the evolution of SIDM subhaloes with high fidelity, from core formation to core-collapse, in staged simulations. Our method works best for small subhaloes (≲1/1000 host mass), for which the error caused by dynamical friction is minimal. We are able to capture the evaporation of subhalo particles by interactions with host halo particles, an effect that has not yet been fully explored in the context of subhalo core-collapse. We find three main processes drive subhalo evolution: subhalo internal heat outflow, host-subhalo evaporation, and tidal effects. The subhalo central density grows only when the heat outflow outweighs the energy gain from evaporation and tidal heating. Thus, evaporation delays or even disrupts subhalo core-collapse. We map out the parameter space for subhaloes to core-collapse, finding that it is nearly impossible to drive core-collapse in subhaloes in SIDM models with constant cross-sections. Any discovery of ultracompact dark substructures with future substructure lensing observations favours additional degrees of freedom, such as velocity-dependence, in the cross-section.

Water vapor distribution and particle condensation growth in turbulent pipe flow

Heterogeneous condensation is a potential particle size-increasing technology that is progressively used in dust removal. In this paper, the condensation growth of fine particles under turbulent pipe flow was investigated. A numerical model was established and verified in terms of gas flow field, relative humidity, and particle size. Results showed that the particles in the center were larger than those in the near-wall area at the outlet of pipe. The mechanism for such improvement was analyzed. The relative humidity in the pipe was nonuniformly distributed, and this was because the low diffusion coefficient of the central water vapor could not effectively supplement the water vapor consumption caused by wall condensation. Furthermore, to achieve superior particle growth, three different spoilers were used to change the gas flow field and water vapor in the pipe. The results indicated that when the spoiler was in the middle, the average particle size increased and the standard deviation decreased, demonstrating an improvement for particle growth. In this case, the changed effective diffusion coefficient of water vapor in the central region can make up for the wall condensation loss without excessive transmission. Consequently, better particle growth was achieved, which was more favorable to particle removal by subsequent equipment. These findings establish theoretical guidance for the treatment of fine particles in the industrial process.

Computational characterization of the behavior of a saliva droplet in a social environment

The conduct of respiratory droplets is the basis of the study to reduce the spread of a virus in society. The pandemic suffered in early 2020 due to COVID-19 shows the lack of research on the evaporation and fate of droplets exhaled in the environment. The current study, attempts to provide solution through computational fluid dynamics techniques based on a multiphase state with the help of Eulerian–Lagrangian techniques to the activity of respiratory droplets. A numerical study has shown how the behavior of droplets of pure water exhaled in the environment after a sneeze or cough have a dynamic equal to the experimental curve of Wells. The droplets of saliva have been introduced as a saline solution. Considering the mass transferred and the turbulence created, the results has showed that the ambient temperature and relative humidity are parameters that significantly affect the evaporation process, and therefore to the fate. Evaporation time tends to be of a higher value when the temperature affecting the environment is lower. With constant parameters of particle diameter and ambient temperature, an increase in relative humidity increases the evaporation time. A larger particle diameter is consequently transported at a greater distance, since the opposite force it affects is the weight. Finally, a neural network-based model is presented to predict particle evaporation time.

Redistribution of total reactive nitrogen in the lowermost Arctic stratosphere during the cold winter 2015/2016

Abstract. During winter 2015/2016, the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with a very strong polar vortex and with the occurrence of extensive polar stratospheric clouds. From mid-December 2015 until mid-March 2016, the German research aircraft HALO (High Altitude and Long-Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than 20 flights have been conducted out of Kiruna, Sweden, and Oberpfaffenhofen, Germany, covering the whole winter period. Besides total reactive nitrogen (NOy), observations of nitrous oxide, nitric acid, ozone, and water were used for this study. Total reactive nitrogen and its partitioning between the gas and particle phases are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. The vertical redistribution of total reactive nitrogen was evaluated by using tracer–tracer correlations (NOy–N2O and NOy–O3). The trace gases are well correlated as long as the NOy distribution is controlled by its gas-phase production from N2O. Deviations of the observed NOy from this correlation indicate the influence of heterogeneous processes. In early winter no such deviations have been observed. In January, however, air masses with extensive nitrification were encountered at altitudes between 12 and 15 km. The excess NOy amounted to about 6 ppb. During several flights, along with gas-phase nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid-containing particles, leading to redistribution of total reactive nitrogen at lower altitudes. Remnants of nitrified air masses have been observed until mid-March. Between the end of February and mid-March, denitrified air masses have also been observed in connection with high potential temperatures. This indicates the downward transport of air masses that have been denitrified during the earlier winter phase. Using tracer–tracer correlations, missing total reactive nitrogen was estimated to amount to 6 ppb. Further, indications of transport and mixing of these processed air masses outside the vortex have been found, contributing to the chemical budget of the winter lowermost stratosphere. Observations within POLSTRACC, at the bottom of the vortex, reflect heterogeneous processes from the overlying Arctic winter stratosphere. The comparison of the observations with CLaMS model simulations confirm and complete the picture arising from the present measurements. The simulations confirm that the ensemble of all observations is representative of the vortex-wide vertical NOy redistribution.