Plume Deposition Research Articles

Determining the Effect of Varying Magmatic Volatile Content on Lunar Magma Ascent Dynamics

AbstractThe Moon is not volcanically active at present, therefore, we rely on data from lunar samples, remote sensing, and numerical modeling to understand past lunar volcanism. The role of different volatile species in propelling lunar magma ascent and eruption remains unclear. We adapt a terrestrial magma ascent model for lunar magma ascent, considering different compositions of picritic magmas and various abundances of H2, H2O, and CO (measured and estimated) for these magmas. We also conduct a sensitivity analysis to investigate the relationship between selected input parameters (pre‐eruptive pressure, temperature, conduit radius, and volatile content) and given outputs (exit gas volume fraction, velocity, pressure, and mass eruption rate). We find that, for the model simulations containing H2O and CO, CO was more significant than H2O in driving lunar magma ascent, for the range of volatile contents considered here. For the simulations containing H2 and CO, H2 had a similar or slightly greater control than CO on magma ascent dynamics. Our results showed that initial H2 and CO content has a strong control on exit velocity and pressure, two factors that strongly influence the formation of an eruption plume, pyroclast ejection, and overall deposit morphology. Our results highlight the importance of (a) quantifying and determining the origin of CO, and (b) understanding the abundance of different H‐species present within the lunar mantle. Quantifying the role of volatiles in driving lunar volcanism provides an important link between the interior volatile content of the Moon and the formation of volcanic deposits on the lunar surface.

Explosive caldera-forming eruptions and debris-filled vents: Gargle dynamics

AbstractLarge explosive volcanic eruptions are commonly associated with caldera subsidence and ignimbrites deposited by pyroclastic currents. Volumes and thicknesses of intracaldera and outflow ignimbrites at 76 explosive calderas around the world indicate that subsidence is commonly simultaneous with eruption, such that large proportions of the pyroclastic currents are trapped within the developing basins. As a result, much of an eruption must penetrate its own deposits, a process that also occurs in large, debris-filled vent structures even in the absence of caldera formation and that has been termed “gargling eruption.” Numerical modeling of the resulting dynamics shows that the interaction of preexisting deposits (fill) with an erupting (juvenile) mixture causes a dense sheath of fill material to be lifted along the margins of the erupting jet. This can cause an eruption that would otherwise produce a buoyant plume and fallout deposits to instead form pyroclastic currents as the dense sheath drives pulsing jet behavior. Increasing thickness of fill amplifies the time variation in jet height. Increasing the fill grain size relative to that of the juvenile particles can result in a much higher jet due to poorer mixing between the dense sheath and the dilute jet core. In all cases, material collapses along the entire height of the dense sheath rather than from the top of a simple fountain. These gargle dynamics provide strong backing for processes that have been inferred to result in intraplinian ignimbrites and simultaneous deposition from high- and low-energy pyroclastic currents.

Sampling Plume Deposits on Enceladus’ Surface to Explore Ocean Materials and Search for Traces of Life or Biosignatures

Abstract Enceladus is unique as an astrobiology target in that it hosts an active plume sourced directly from its habitable subsurface ocean. Ice particles from the plume contain geochemical constituents that are diagnostic of the ocean conditions, and may hold traces of life and/or biosignatures, if they exist. Up to 93% of the plume particles fall back onto the surface of Enceladus. The low radiation environment and present-day activity are favorable to the preservation of any complex organics and putative biosignatures contained within these particles. Laboratory experiments and modeling suggest that plume deposits would likely be weakly consolidated and relatively easy to sample. Sampling systems like a dual rasp, under development to achieve technology readiness level (TRL) 5 in 2021, would enable a landed mission on Enceladus’ surface to acquire large amounts of surface materials, a requirement for analysis of trace constituents. A landed mission on Enceladus could greatly enhance our understanding of the chemical makeup of plume particles and the subsurface ocean, and seek traces of life and/or biosignatures.

Quality control of computational fluid dynamics (CFD) model of ozone reaction with human surface: Effects of mesh size and turbulence model

Indoor chemical reactions with human surfaces can meaningfully affect indoor pollutant dynamics and human exposure to reactants and products. Computational Fluid Dynamics models have been used to simulate ozone-human surface reactions in indoor environments. However, the model uncertainties due to near-human grid size and turbulence model are not well understood. The objective of this study is to assess performance of turbulence models and near-human surface grids in predicting local airflow and ozone transport near the human surface under a representative range of indoor airflow conditions. The results show that Large Eddy Simulation (LES) with a fine near-human grid size (e.g., y+ = 1) can yield reasonable results of airflow and mass transfer near the body. The SST k–ω model performs well for the simulation of near-human airspeed, whereas the standard k–ε model can predict lower airspeeds above the human head than the measurements. Both standard k–ε and SST k–ω models may underestimate the turbulent kinetic energy of the thermal plume and ozone deposition velocity at the human surface. The results also suggest that near-human grid sizes of y+ >10 can lead to unreasonable estimates of airflow and mass transfer rate near the human surface.

Strength Evolution of Ice Plume Deposit Analogs of Enceladus and Europa

AbstractEnceladus and possibly Europa spew materials from their internal ocean into their exosphere, some of which are deposited back onto the surface of those Ocean Worlds. This setting provides a unique opportunity to seek traces of past or extant life in ice plume deposits on their surfaces. However, the design of lander missions and surface sampling techniques and the choice of sampling locations rely heavily on strength expectations. Here we present an experimental investigation of the evolution in strength of ice plume deposit analogs at several temperatures, as well as a model that predicts first‐order estimates of the strength of evolved ice plume deposits under geologic timescales relevant to Enceladus and Europa. These results suggest that plume deposits remain weak and poorly consolidated on Enceladus, while they may develop substantial strength (comparable to solid ice) within <100 Myr on Europa.

Foraminiferal Patterns in Deglacial Sediment in the Western Ross Sea, Antarctica: Life Near Grounding Lines

AbstractImproved multibeam swath bathymetry allows targeted coring of glacial landforms aiming at improving our understanding of sedimentary facies that developed in glacimarine settings during the post‐Last Glacial Maximum (LGM) deglaciation. Coupled with radiocarbon dates, we explore foraminiferal records from 18 sediment cores from the western Ross Sea largely from sites near paleo–grounding lines. We investigate post‐LGM foraminiferal assemblages from glacimarine environments, including those proximal and more distal to paleo–grounding lines, including environments influenced by subglacial meltwater outflow and further removed from direct glacial influence and subject to different oceanographic conditions. Agglutinated benthic foraminiferal assemblages dominate open marine facies deposited under the presence of High Salinity Shelf Water and significant primary production, while calcareous foraminiferal assemblages characterize grounding line‐proximal settings, some of which were potentially influenced by Modified Circumpolar Deep Water. Rapid deposition of meltwater plume deposits inhibited and, in some cases, significantly altered foraminifera abundance and diversity. Broadly in the Ross Sea, it appears that the high bathymetric gradient of grounding zone wedges is a key factor promoting rich benthic foraminiferal communities in habitats proximal to grounding lines. Therefore, we demonstrate that paleo–grounding line settings may archive high quality in situ foraminiferal data, which is imperative for paleoenvironmental and geochemical studies on glaciated continental margins worldwide.

Characterizing deposits emplaced by cryovolcanic plumes on Europa

In the absence of direct observations of Europa's particle plumes, deposits left behind during eruptive events would provide the best evidence for recent geological activity, and would serve as indicators of the best places to search for ongoing activity on the icy moon. Here, we model the morphological and spectral signatures of europan plume deposits, utilizing constraints from recent Hubble Space Telescope observations as model inputs. We consider deposits emplaced by plumes that are 1 km to 300 km tall, and find that in the time between the Galileo Mission and the arrival of the Europa Clipper spacecraft, plumes that are <7 km tall are most likely to emplace deposits that could be detected by spacecraft cameras. Deposits emplaced by larger plumes could be detected by cameras operating at visible wavelengths provided that their average particle size is sufficiently large, their porosity is high, and/or they are salt-rich. Conversely, deposits emplaced by large plumes could be easily detected by near-IR imagers regardless of porosity, or individual particle size or composition. If low-albedo deposits flanking lineated features on Europa are indeed cryoclastic mantlings, they were likely emplaced by plumes that were <4 km tall, and deposition could be ongoing today. Comparisons of the sizes and albedos of these deposits between the Galileo and Europa Clipper missions could shed light on the size and frequency of cryovolcanic eruptions on Europa.

Analytical Solution of Advection‐Dispersion Boundary Value Processes in Environmental Flows

AbstractThe one‐dimensional advection‐dispersion equation with streamwise boundaries has been used to model a wide range of real‐world processes including groundwater contaminant transport, atmospheric plume deposition, and the movement of planktonic organisms and migratory animals through riverine systems. Imposing boundary conditions at upstream and downstream locations complicates the analysis of this equation, and processes that require such boundary conditions are, therefore, typically modeled using approximations that are valid only under certain conditions. Approximations typically involve a simplification of the mass influx into the system, require a large separation between source and boundary, or work only in either strongly advection‐ or strongly dispersion‐dominated systems. Here, we circumvent these limitations by providing an analytical solution to a class of advection‐dispersion equations that are broadly applicable to the processes described above as well as many other physical and biological problems. Our solution makes it possible to relax the assumptions required under previous analytic approximations, making it a more flexible approach for modeling advection‐dispersion processes under realistic field conditions. We show that the solution is in good agreement with random walk simulations. To illustrate the broad utility of the method, we also apply it to an empirical data set from a population of migratory fish moving through a river system in the California Central Valley and demonstrate that it describes the data more accurately than do existing methods.

Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation, Gale crater, Mars

AbstractRecent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 103 to 107 Earth years.

Nonlinear Spectral Unmixing for the Characterisation of Volcanic Surface Deposit and Airborne Plumes from Remote Sensing Imagery

In image processing, it is commonly assumed that the model ruling spectral mixture in a given hyperspectral pixel is linear. However, in many real life cases, the different objects and materials determining the observed spectral signatures overlap in the same scene, resulting in nonlinear mixture. This is particularly evident in volcanoes-related imagery, where both airborne plumes of effluents and surface deposit of volcanic ejecta can be mixed in the same observation line of sight. To tackle this intrinsic complexity, in this paper, we perform a pilot test using Nonlinear Principal Component Analysis (NLPCA) as a nonlinear transformation, that projects a hyperspectral image onto a reduced-dimensionality feature space. The use of NLPCA is twofold: (1) it is used to reduce the dimensionality of the original spectral data and (2) it performs a linearization of the information, thus allowing the effective use of successive linear approaches for spectral unmixing. The proposed method has been tested on two different hyperspectral datasets, dealing with active volcanoes at the time of the observation. The dimensionality of the spectroscopic problem is reduced of up to 95% (ratio of the elements of compressed nonlinear vectors and initial spectral inputs), by the use of NLPCA. The selective use of an atmospheric correction pre-processing is applied, demonstrating how individual plume and volcanic surface deposit components can be discriminated, paving the way to future application of this method.

Flocculation in a decaying shear field and its implications for mud removal in near‐field river mouth discharges

AbstractWe measure the change in floc size in a decaying shear field that mimics the decay found in a river mouth discharge. The primary questions explored are: (1) how far from equilibrium are the flocs during the decay? And, (2) how significant are the changes in size, and hence settling velocity, brought on by the changes in shear when it comes to predicting settling flux? These questions are examined in the laboratory using a camera system that allows for flocs to be sized within a turbulent suspension. We also examine how inclusion of various approaches to account for flocculation impacts the plume concentration and deposition rates in a simple river mouth discharge model. In the experiments, flocs grew from their initial size of 20–50 μm up to 100–200 μm due only to changes in shear over time scales of decay similar to those in a small river mouth discharge. It is estimated that such growth would lead to fourfold or greater fold increase in the mud settling velocity within the first few kilometers from the river mouth, even though floc sizes were only 0.5–0.8 of their equilibrium values. The plume modeling highlights the strong dependence of the mud deposition rate on the method chosen to account for flocs, and the importance of the settling to entrainment velocity ratio in dictating plume concentrations.

Morphological and Sedimentological Signatures of Late Holocene Prodelta Lobes in Lingayen Gulf, Philippines

ABSTRACT Mateo, Z.R.P. and Siringan, F.P., 2016. Morphological and sedimentological signatures of Late Holocene prodelta lobes in Lingayen Gulf, Philippines. Delta switching is an integral part of coastal evolution and may be caused by a combination of autogenic and allogenic factors. We present offshore signatures of modern and ancient prodelta deposits that document delta switching in the bayhead region of Lingayen Gulf, NW Philippines. Prodelta lobes of prograding systems are marked by areas of shoaling of about 6 m within 95 years, with around 30% clay, whereas abandoned deltas are manifested as areas of deepening of around 3 m with as much as 80% sand. The sorting and kurtosis of the mud fraction further categorize recent and current sedimentary environments and processes such as erosional and shoreface environments and areas dominated by sediment plume and normal offshore deposition. High-resolution subbottom profiles reveal the stacked and truncated nature of different prodelta lobes associated wit...

Examining the influence of meteorological simulations forced by different initial and boundary conditions in volcanic ash dispersion modelling

The performance of the combination of the FALL3D ash dispersion model with the Weather Research and Forecast (WRF) meteorological model in the southern cone of South America under two initial and boundary conditions was evaluated. ERA-Interim and NCEP-GFS datasets were used as dynamic conditions by WRF to simulate meteorological fields for FALL3D. As a study case, we used the eruption of the Puyehue–Cordón Caulle Volcanic Complex occurred in Chile in June 2011. The simulated meteorological results were compared with the horizontal wind direction, meridional and zonal wind components, air and dew point temperatures of 7 radio sounding stations using a set of error indicators. In addition, the ash mass load simulated by FALL3D for a day of maximum dispersion of volcanic ash was evaluated using the Moderate Resolution Imaging Spectroradiometer (MODIS) data, on which the Prata algorithm was applied. As well as this, the WRF-dominant physical processes with both dynamic conditions were analyzed for that same date.Meteorological results indicated that the simulation performed with WRF and NCEP-GFS shows the lowest errors at levels between 925 and 300hPa. Ash dispersion simulated with FALL3D and WRF in both dynamic conditions shows a different perfomance, which from the synoptic and dynamic viewpoint can be explained for the result of wind intensity and geopotential height. Moreover, WRF intiliazed with NCEP-GFS and FALL3D has a higher degree of concordance with the MODIS image. Based on the analysis and results, it was concluded that for the southern cone of South America, 1) it was not trivial for the simulation of volcanic ash dispersion to use one dynamic condition or another in WRF; 2) in that sense, meteorological variables that influenced the differences in volcanic ash dispersion were horizontal wind intensity and direction and geopotential heights; 3) the system generated from the combination of the WRF model initialized with NCEP-GFS and the FALL3D dispersion model would provide better estimations of ash plume position and deposition in the region.

Predicting and Controlling Nuclear Accident Hazards: Issues and Challenges

ABSTRACTGlobal nuclear security is threatened by nuclear accidents and the purposeful use of nuclear weapons. Accordingly, atmospheric pollution prediction and control for nuclear accidents, including identifying sources in nuclear or radiological incidents, predicting hazards to persons and environments, and optimally controlling accident hazards, are current areas of nuclear security research. Source inversion, hazard prediction, and optimal control are three interrelated key issues for nuclear accident emergencies. Although progress has been made in hazard prediction for nuclear accidents since the 1970s and some source inversion methods were presented after the Fukushima nuclear accident, optimal control methods are rarely reported, source inversion methods are less practical, and prediction accuracy remains unsatisfactory. Thus, novel theories are required for optimal control and source inversion for nuclear accidents, and to develop methods for simulating the influences of radioactive plume dispersion and deposition under complex meteorological and terrain conditions. This work reviews the current progress, uncertainties, and research needs in nuclear security. In addition, a rapid source inversion method based on the Lagrangian model is developed and implemented in a test case. To address future challenges, an innovative architecture for Atmospheric Pollution Prediction and Optimal Control System for nuclear accidents (APPOCS) is proposed, and the perspectives are generalized to promote future research on nuclear accident hazard prediction and optimal control. At this time, forward-looking ideas and revolutionary perspectives are required to foster nuclear security research in the academic community.

Phosphorus mobility under short-term anoxic conditions in two shallow eutrophic coastal systems (Curonian and Sacca di Goro lagoons)

The effects of short-term anoxia on phosphorus mobility were investigated in estuarine sediments collected from two eutrophic European lagoons. Study areas differ with regard to climate and salinity: the boreal Curonian Lagoon (Lithuania) is oligohaline while the Mediterranean Sacca di Goro (Italy) is mesohaline. In each lagoon two sites were chosen representing areas impacted by river plume discharge and areas impacted by high organic matter deposition. Benthic fluxes of dissolved oxygen, inorganic phosphorus (DIP), iron (Fe2+) and manganese (Mn2+) were measured by dark intact core incubations in oxic and anoxic conditions. The latter were induced by incubation prolonged by up to 40 h depending on oxygen consumption rates. Solid phase P pools and pore water profiles of DIP, Fe2+, Mn2+ and sulfides were also measured before and after the induction of anoxia. Although incubation temperature and organic matter content were similar in plume and organic impacted areas of the two estuaries, higher benthic oxygen consumption rates were observed in Sacca di Goro, suggesting higher reactivity of the organic pool. Short-term anoxia had a significant effect on benthic fluxes of DIP (sulfide and Fe2+) only at the organic-rich and saline site of Sacca di Goro while internal buffers prevented inorganic P regeneration at the remaining sites. However, the analysis of pore water and solid phase pools revealed large variations during the transition and provided insights on the mechanisms controlling P dynamics. Both stations influenced by river plume deposition had high total inorganic P content (but most of it was refractory) and high reactive Mn pools, continuously regenerated by ventilation and irrigation of sediments by macrofauna. In these sites, oxygen depletion resulted in large accumulation of reduced Mn in the pore water but high fluxes of Mn2+ were also measured in the oxic part of the incubation suggesting the relevance of this respiration process. Thus Mn reduction preserved oxidized Fe pool and ultimately prevent P mobilization. Our results suggest that fluxes of DIP across the sediment–water interface are controlled by an array of different and site-specific mechanisms. These biogeochemical buffers are effective and contrast massive P release to the water column in highly productive systems as coastal lagoons, where episodes of transient oxygen shortage are frequent.

PHOTOMETRY OF PLUTO 2008–2014: EVIDENCE OF ONGOING SEASONAL VOLATILE TRANSPORT AND ACTIVITY

The New Horizons spacecraft will encounter Pluto in 2015 July. As this fast flyby will yield a picture of Pluto frozen in time, ground-based observations are key to understanding this dwarf ice planet, especially with regard to the seasonal transport of surface volatiles. This paper reports on changes in Pluto's rotational light curve as evidence for this transport. Historical observations are consistent with a stable frost pattern, but since 2002, changes began to appear in both light curves and Hubble Space Telescope maps. Our BVR observations at Table Mountain Observatory from 2008 to 2014 show evidence for sustained and continued albedo and color changes on Pluto. The B and V albedos are stable, but Pluto is becoming redder in color, particularly on its low-albedo side. This view is consistent with the transport of a bright volatile (nitrogen) with the uncovering of a substrate of red material such as photolyzed methane. As Buie et al. reported a B – V of 0.96 in 2002–2003, and our B – V was higher in 2008–2012, Pluto may have experienced a transient reddening in the 1999–2012 period. We also discovered an opposition supersurge in all three colors at very small solar phase angles (∼0.°10). Explosive geysers have been observed on Triton and Mars, the two other celestial bodies with receding polar caps. Because the physical conditions existing on Pluto are similar to those on Triton, we predict that plume deposits and possibly active plumes will be found on its surface.

Laser ablation and deposition of titanium dioxide with ultrashort pulses at 527 nm

We report an experimental analysis on laser ablation and deposition of TiO2 with ≈300-fs, 527-nm ultrashort laser pulses. We particularly address the following: (1) the dependence of the deposition rate on the laser fluence, in high-vacuum conditions; (2) the effect of an oxygen background gas pressure on the expansion of the ablated species and on the deposition rate. Two different regimes are observed for the dependence of the deposition rate in high vacuum: The first one governed by two-photon absorption occurring close to the ablation threshold is, then, followed by the second, thermal dependence at larger fluences. The propagation of the atomic and nanoparticulate plumes produced in ultrashort laser ablation are influenced in a quite different way by the background gas pressure, which eventually reflects on the variation of the deposition rate with pressure. Moreover, it is observed that the ablated material is predominantly composed of nanoparticles (≈70 %), similar to what was reported before in the case of elemental metallic targets. Finally, plume deposition results in the formation of nanoparticle-assembled films with a variation of the characteristics morphology with the background gas pressure.

Horizontal Resolution Dependence of Atmospheric Simulations of the Fukushima Nuclear Accident Using 15-km, 3-km, and 500-m Grid Models

We investigated the horizontal resolution dependence of atmospheric radionuclide (Cs-137) simulations of the Fukushima nuclear accident on March 15, 2011. We used Eulerian and Lagrangian transport models with low- (15-km), medium- (3-km), and high- (500-m) resolutions; both models were driven by the same meteorological analysis that was prepared by our data assimilation system (NHM-LETKF) for each horizontal resolution. This preparation was necessary for the resolution-dependent investigation, excluding any interpolation or averaging of meteorological fields. In the results, the 15-km grid analysis could not reproduce Fukushima’s mountainous topography in detail, and consequently failed to depict a complex wind structure over mountains and valleys. In reality, the Cs-137 plume emitted from the Fukushima Daiichi Nuclear Power Plant (FDNPP) was mostly blocked by Mt. Azuma and other mountains along the Naka-dori valley after crossing over Abukuma Mountains on March 15, 2011. However, the 15-km grid simulations could not represent the blockage of the Cs-137 plume, which unnaturally spread through the Naka-dori valley. In contrast, the 3-km and 500-m grid simulations produced very similar Cs-137 concentrations and depositions, and successfully produced the plume blockage and deposition along the Naka-dori valley. In conclusion, low-resolution (15-km grid or greater) atmospheric models should be avoided for assessing the Fukushima nuclear accident when a regional analysis is needed. Meanwhile, it is reasonable to use 3-km grid models instead of 500-m grid models due to their similarities and the high computational burden of 500-m grid model simulations.

The Kinetics of De-agglomeration of Magnesium Stearate Dry-Coated Salbutamol Sulphate Powders

The objective was to investigate the effect of dry coating of salbutamol sulphate (SS) with magnesium stearate (MgSt) on the kinetics of powder de-agglomeration. The relative de-agglomeration of the MgSt coated SS powders was higher than uncoated SS at all air flow rates; the SS coated with 2 % MgSt showed the highest extent of de-agglomeration (> 5 % MgSt coated SS > 1 % MgSt coated SS). Rate of de-agglomeration was described by a cumulative de-agglomerated versus time profile. Profiles fitted a mono-exponential model and the de-agglomeration rate constant (kd) was estimated. No significant differences existed between any of the uncoated and coated powders. The significance of this study relates to the improved aerosolization and de-agglomeration performance of the MgSt coated SS powders with optimum performance of 2 % MgSt coated SS. More significant is the finding that no change existed in de-agglomeration rate constants between the coated and uncoated powders, with the potential implications that their aerosol plume concentration and deposition patterns were similar.

Modeling of leachable 137Cs in throughfall and stemflow for Japanese forest canopies after Fukushima Daiichi Nuclear Power Plant accident

The Fukushima accident dispersed significant amounts of radioactive cesium (Cs) in the landscape. Our research investigated, from June 2011 to November 2013, the mobility of leachable Cs in forests canopies. In particular, 137Cs and 134Cs activity concentrations were measured in rainfall, throughfall, and stemflow in broad-leaf and cedar forests in an area located 40km from the power plant.Leachable 137Cs loss was modeled by a double exponential (DE) model. This model could not reproduce the variation in activity concentration observed. In order to refine the DE model, the main physical measurable parameters (rainfall intensity, wind velocity, and snowfall occurrence) were assessed, and rainfall was identified as the dominant factor controlling observed variation. A corrective factor was then developed to incorporate rainfall intensity in an improved DE model.With the original DE model, we estimated total 137Cs loss by leaching from canopies to be 72±4%, 67±4%, and 48±2% of the total plume deposition under mature cedar, young cedar, and broad-leaf forests, respectively. In contrast, with the improved DE model, the total 137Cs loss by leaching was estimated to be 34±2%, 34±2%, and 16±1% of the total plume deposition under mature cedar, young cedar, and broad-leaf forests, respectively. The improved DE model corresponds better to observed data in literature.Understanding 137Cs and 134Cs forest dynamics is important for forecasting future contamination of forest soils around the FDNPP. It also provides a basis for understanding forest transfers in future potential nuclear disasters.