21 research outputs found
Fumarole compositions and mercury emissions from the Tatun Volcanic Field, Taiwan: Results from multi-component gas analyser, portable mercury spectrometer and direct sampling techniques
No full textRapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna’s emissions
Full text linkA major uncertainty regarding the environmental impacts of volcanic Hg is the extent to which Hg is deposited locally or transported globally. An important control on dispersion and deposition is the oxidation state of Hg compounds: Hg(0) is an inert, insoluble gas, while Hg(II) occurs as reactive gases or in particles, which deposit rapidly and proximally, near the volcanic vent. Using a new high temperature thermodynamic model, we show that although Hg in Etna's magmatic gases is almost entirely Hg(0) (i.e., gaseous elemental mercury), significant quantities of Hg(II) are likely formed at Etna's vents as gaseous HgCl2, when magmatic gases are cooled and oxidised by atmospheric gases. These results contrast with an earlier model study and allow us to explain recent measurements of Hg speciation at the crater rim of Etna without invoking rapid (< 1 min) low temperature oxidation processes. We further model Hg speciation for a series of additional magmatic gas compositions. Compared to Etna, Hg(II) production (i.e., Hg(II)/Hgtot) is enhanced in more HCl-rich magmatic gases, but is independent of the Hg, HBr and HI content of the magmatic gases. Hg(II) production is not strongly influenced by the initial oxidation state of magmatic gases above NNO, although production is hindered in more reduced magmatic gases. The model and results are widely applicable to other open-vent volcanoes and may be used to improve the accuracy of chemical kinetic models for low temperature Hg speciation in volcanic plumes
Conception d'un moteur asynchrone adapté à une double alimentation (réduction des pertes supplémentaires induites par une alimentation de type M.L.I.)
No full textCe mémoire traite des pertes supplémentaires développées asynchrones de fortes puissances. Le premier chapitre est consacré à la modélisation de l'ensemble machine-convertisseurs en régime sinusoïdal et non sinusoïdal. L'auteur y développe un calcul analytique des diverses inductances des enroulements statoriques et rotoriques en fonction des différents paramètres géométriques de la machine. Il met en évidence quelques caractéristiques offertes par la double alimentation telle que la possibilité de réduire considérablement les pertes fer dans le cas d'une machine à champs rotorique et statorique inverses. Le second chapitre s'intéresse au choix des dimensions des conducteurs et de leur subdivision pour différentes configurations de bobinage ainsi que l'influence de la température sur les pertes supplémentaires. Les expressions analytiques sont calculées à partir d'un modèle monodirectionnel. L'auteur met en évidence pour chaque type d'enroulement et motif d'alimentation l'existence d'une hauteur critique des conducteurs qui minimise les pertes par effet Joule. Le troisième chapitre traite des pertes fer supplémentaires. L'auteur s'appuie sur une approche expérimentale et une modélisation thermique de la machine. L'étude est menée sur une macvhine asynchrone de 4kW équipée au stator de thermocouples. Des essais d'échauffements pour différents motifs d'alimentation ont permis de trouver une loi permettant de prédire les pertes de fer à partir de celles obtenues en régime sinusoïdal en fonction du taux de distorsion et de la fréquence de découpage du signal d'alimentation. Dans le quatrième chapitre l'auteur compare pour une machine connue, les pertes pour différents types de commande M.L.I. L'auteur montre que la commande à E/f=Cte suit le même profil que les pertes en régime sinusoïdal avec une majoration et que celles-ci sont largement inférieures à celles obtenues avec une M.L.I. sinus-triangle ou M.L.I calculée.This memory treats about additional losses developed in high power induction motors. The first chapter is devoted to the modelling of the machine-converters association with sinusoidal and nonsinusoidal wave forms. The author develops an analytical calculation of the different inductances of the stator and rotor windings according to the geometrical parameters of the machine. It underlines some characteristics offered by the double feeding such as the possibility of reducing considerably the iron losses in the case of opposite rotor and stator fields. The second chapter relates to the choice of the dimensions of the wires and of their subdivisions for different configurations of windings and discusses the temperature influence on the additional losses. The analytical expressions are calculated with a one-dimensional model. The author underlines that for each type of winding and current wave form, a critical height of the conductors which minimises the copper losses exists. The third chapter treats on additional iron losses. The author uses an experimental approach and a thermal modelling of the machine. The study is undertaken on an asynchronous machine of 4kW equipped at the stator with thermocouples. Temperature-rise tests for various voltage wave forms made it possible to find a law for predicting the iron losses from those obtained in sinusoidal mode according to the distortion rate and the sampling frequency of the signal. In the fourth chapter the author compares for a known machine, the losses for different type of PWM control. The author shows that the law with E/f=Constant follows the same profile as the losses in sinusoidal mode but with an increase and that they are largely lower than those obtained with a sine-triangle PWM or for a calculated PWM.BELFORT-BU L. FEBVRE (900102102) / SudocSudocFranceF
Environmental effects of ashfall in Argentina from the 2008 Chaitén volcanic eruption
Full text linkAnalyses of air, water and vegetation samples collected in June 2008 offer new insights into the environmental effects of the May 2008 Chaitén eruption on Argentina, which was subject to significant ashfall between 42°S and 46°S.Results from air filtration in the ash-affected town of Esquel (with samples analysed by gravimetry and scanning electron microscopy) show the total mass of resuspended ash in the air is well-correlated with traffic activity. However, this variation is primarily related to varying amounts of the largest particles, with little variation in the amounts of fine ash particles (i.e., d < 4 ?m). This result suggests that the hazard associated with resuspended ash remains high even when traffic activity is low and the air is not visibly dusty. We estimate PM2.5 not, vert, similar 200 ?g m? 3, PM4 not, vert, similar 300 ?g m? 3 and PM10 not, vert, similar 1000 ?g m? 3; these concentrations far exceed WHO air quality guidelines and likely persisted for several months.Results from water and vegetation sampling (with samples analysed by inductively coupled plasma mass spectrometry and ion chromatography) indicate that ashfall resulted in significant compositional changes in ephemeral lakes and coirón grass (Festuca pallescens). For B, Cd, Zn, Tl, Cu and Ni, there are strong linear correlations between concentrations and ash thickness (where > 2 mm) in both datasets. These results suggest that the eruption of Chaitén led to significant changes in the concentrations of trace volatile elements within the environment. Analysis of vegetation samples collected in January 2009 indicates that the elevated element concentrations in coirón grass persisted for < 8 months. These results offer insights into the environmental fate of volatile trace elements emitted during volcanic eruptions
Bioindication of volcanic mercury (Hg) deposition around Mt. Etna (Sicily)
No full textMt. Etna is a major natural source of Hg to the Mediterranean region. Total mercury concentrations, [Hg]tot, in Castanea sativa (sweet chestnut) leaves sampled 7–13 km from Etna's vents (during six campaigns in 2005–2011) were determined using atomic absorption spectroscopy. [Hg]tot in C. sativa was greatest on Etna's SE flank reflecting Hg deposition from the typically overhead volcanic plume. [Hg]tot also showed Hg accumulation over the growing season, increasing with leaf age and recent eruptive activity. [Hg]tot in C. sativa was not controlled by [Hg]tot in soils, which instead was greatest on Etna's NW flank, and was correlated with the proportion of organic matter in the soil (% Org). An elevated [Hg]tot/% Org ratio in soils on Etna's SE flank is indicative of increased Hg deposition. This ratio was also found to decrease with local soil pH, suggesting that Hg deposited to the low pH and organic-poor soils on Etna's SE flank may not be retained but will instead be released to groundwater or re-emitted to the atmosphere. These results show that the deposition of volcanic Hg has clear impacts and confirm that Etna is an important source of Hg to the local environmen
Halogens and trace metal emissions from the ongoing 2008 summit eruption of Kīlauea volcano, Hawaìi
Full text linkVolcanic plume samples taken in 2008 and 2009 from the Halemàumàu eruption at Kīlauea provide new insights into Kīlauea's degassing behaviour. The Cl, F and S gas systematics are consistent with syn-eruptive East Rift Zone measurements suggesting that the new Halemàumàu activity is fed by a convecting magma reservoir shallower than the main summit storage area. Comparison with degassing models suggests that plume halogen and S composition is controlled by very shallow (77%) as gaseous elemental mercury at the point of emission. Sulphate is an important aerosol component (modal particle diameter ∼0.44μm). Aerosol halide ion concentrations are low compared to other systems, consistent with the lower proportion of gaseous hydrogen halides. Plume concentrations of many metallic elements (Rb, Cs, Be, B, Cr, Ni, Cu, Mo, Cd, W, Re, Ge, As, In, Sn, Sb, Te, Tl, Pb, Mg, Sr, Sc, Ti, V, Mn, Fe, Co, Y, Zr, Hf, Ta, Al, P, Ga, Th, U, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm) are elevated above background air. There is considerable variability in metal to SO 2 ratios but our ratios (generally at the lower end of the range previously measured at Kīlauea) support assertions that Kīlauea's emissions are metal-poor compared to other volcanic settings. Our aerosol Re and Cd measurements are complementary to degassing trends observed in Hawaiian rock suites although measured aerosol metal/S ratios are about an order of magnitude lower than those calculated from degassing trends determined from glass chemistry. Plume enrichment factors with respect to Hawaiian lavas are in broad agreement with those from previous studies allowing similar element classification schemes to be followed (i.e., lithophile elements having lower volatility and chalcophile elements having higher volatility). The proportion of metal associated with the largest particle size mode collected (>2.5μm) and that bound to silicate is significantly higher for lithophiles than chalcophiles. Many metals show higher solubility in pH 7 buffer solution than deionised water suggesting that acidity is not the sole driver in terms of solubility. Nonetheless, many metals are largely water soluble when compared with the other sequential leachates suggesting that they are delivered to the environment in a bioavailable form. Preliminary analyses of environmental samples show that concentrations of metals are elevated in rainwater affected by the volcanic plume and even more so in fog. However, metal levels in grass samples showed no clear enrichment downwind of the active vents. © 2011 Elsevier Ltd
Application and evaluation of biomagnetic and biochemical monitoring of the dispersion and deposition of volcanically-derived particles at Mt. Etna, Italy
No full textBiomagnetic monitoring, using tree leaves as passive surfaces for particle collection, has been shown to be a promising technique for assessing the dispersion and deposition of particles in the context of anthropogenic pollution. By comparing leaves' magnetic properties with trace metal levels measured in the leaves, we here assess the utility of the biomagnetic technique as a sensitive, fast and inexpensive method for assessment of volcanic plume deposition. Samples of sweet chestnut leaves (Castanea sativa) were collected from the area surrounding Mt. Etna volcano in Sicily during the 2008 growing season when the volcano was displaying mild eruptive activity. Previous work has shown that the trace metal concentrations of these leaves show promise as a bio-indicator of volcanic gas, aerosol and ash deposition on the flanks of Mt. Etna. For 2008, ICPMS analysis of the elemental abundances within the leaves showed that As, Cd, Cu, Mo, Tl, K, B, Al and Co displayed elevated concentrations downwind of the volcanic source, to the E–ESE, but with overall reduced concentrations relative to 2007. Less explosive activity than 2007 and a broader, more easterly wind field may have distributed the volcanic plume over a wider area, both of which would account for reduced trace element concentrations in 2008. Correspondence of elevated concentrations in both years (2007 and 2008) with their respective wind fields suggests that plume deposition is the controlling factor rather than variability in the soils and that these leaves do indeed have potential as bio-indicators of the plume's dispersion. Magnetic analysis of the leaves shows that the spatial distribution of saturation isothermal remanent magnetisation (SIRM) and magnetic susceptibility (χlf) values display a strong correlation with the wind-influenced plume transport direction for 2008, with elevated concentrations of magnetic minerals on the eastern flanks, in broad agreement with the ICP-MS data. This spatial distribution provides further evidence of plume variability as the main control on the concentrations of magnetic particles on the leaf surfaces and on elemental uptake by the tree and suggests that biomagnetic monitoring may also hold promise as a method of assessing the dispersion and impacts of volcanic plumes. The dominant magnetic mineral on the leaf surfaces is a magnetite-like mineral (contributing >90% of the SIRM), of coarse, multidomain (MD) grain size (∼5 to 15μm). A volcanogenic source is most likely, as magnetites from anthropogenic sources are typically an order of magnitude smaller in grain size (∼0.1–1 μm). These new results from the use of environmental magnetism on leaves, in a volcanically-affected region, suggest that biomagnetic monitoring offers a new, sensitive and rapid means for the assessment of volcanic plume deposition over wide areas
Nonparametric signed‐rank control charts with variable sampling intervals
Full text linkVariable sampling interval (VSI) charts have been proposed in the literature for normal theory (parametric) control charts and are known to provide performance enhancements. In the VSI setting, the time between monitored samples is allowed to vary depending on what is observed in the current sample. Nonparametric (distribution‐free) control charts have recently come to play an important role in statistical process control and monitoring. In this paper a nonparametric Shewhart‐type VSI control chart is considered for detecting changes in a specified location parameter. The proposed chart is based on the Wilcoxon signed‐rank statistic and is called the VSI signed‐rank chart. The VSI signed‐rank chart is compared with an existing fixed sampling interval signed‐rank chart, the parametric VSI X‐chart, and the nonparametric VSI sign chart. Results show that the VSI signed‐rank chart often performs favourably and should be used.The South African Research Chairs Initiative at the University of Pretoria and by the Department of Information Systems, Statistics and Management Science, University of Alabama. Marien Graham's research was also supported by the National Research Foundation (Thuthuka programme: TTK14061168807; grant number: 94102), SARCHI Award to the third author from the National Research Foundation.http://wileyonlinelibrary.com/journal/qre2018-12-21hj2018Statistic
Mercury emissions and stable isotopic compositions at Vulcano Island (Italy)
No full textSampling and analyses methods for determining the stable isotopic compositions of Hg in an active volcanic
system were tested and optimized at the volcanic complex of Vulcano (Aeolian Islands, Italy). Condensed
gaseous fumarole Hg(fum)
T , plume gaseous elemental Hg(g)
0 and plume particulate Hg(p)
II were obtained at
fumaroles F0, F5, F11, and FA. The average total Hg emissions, based on HgT/SO2 in condensed fumarolic gases
and plumes, range from 2.5 to 10.1 kg y−1, in agreement with published values [Ferrara, R., Mazzolai, B.,
Lanzillotta, E., Nucaro, E., Pirrone, N., 2000. Volcanoes as emission sources of atmospheric mercury in the
Mediterranean Basin. Sci. Total Environ. 259(1–3), 115–121; Aiuppa, A., Bagnato, E., Witt, M.L.I., Mather, T.A.,
Parello, F., Pyle, D.M., Martin, R.S., 2007. Real-time simultaneous detection of volcanic Hg and SO2 at La Fossa
Crater, Vulcano (Aeolian Islands, Sicily). Geophys. Res. Lett. 34(L21307).]. Plume Hg(p)
II increases with distance
from the fumarole vent, at the expense of Hg(g)
0 and indicates significant in-plume oxidation and
condensation of fumarole Hg(fum)
T .
Relative to the NIST SRM3133 Hg standard, the stable isotopic compositions of Hg are δ202Hg(fum)
T =−0.74‰±0.18
(2SD, n=4) for condensed gaseous fumarole Hg(fum)
T , δ202Hg(g)
0 =−1.74‰±0.36 (2SD, n=1) for plume gaseous
elemental Hg(g)
0 at the F0 fumarole, and δ202Hg(p)
II =−0.11‰±0.18 (2SD, n=4) for plume particulate Hg(p)
II . The
enrichment of Hg(p)
II in the heavy isotopes and Hg(g)
0 in the light isotopes relative to the total condensed fumarolic
Hg(fum)
T gas complements the speciation data and demonstrates a gas-particle fractionation occurring after the gas
expulsion inambient T° atmosphere. A first order Rayleigh equilibriumcondensation isotope fractionation model
yields a fractionation factor αcond-gas of 1.00135±0.00058.Published236-2431.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveJCR Journalope
Rapid oxidation of mercury (Hg) at volcanic vents: Insights from high temperature thermodynamic models of Mt Etna's emissions
No full textA major uncertainty regarding the environmental impacts of volcanic Hg is the extent to which Hg is deposited locally or transported globally. An important control on dispersion and deposition is the oxidation state of Hg compounds: Hg(0) is an inert, insoluble gas, while Hg(II) occurs as reactive gases or in particles, which deposit rapidly and proximally, near the volcanic vent. Using a new high temperature thermodynamic model, we show that although Hg in Etna's magmatic gases is almost entirely Hg(0) (i.e., gaseous elemental mercury), significant quantities of Hg(II) are likely formed at Etna's vents as gaseous HgCl2, when magmatic gases are cooled and oxidised by atmospheric gases. These results contrast with an earlier model study and allow us to explain recent measurements of Hg speciation at the crater rim of Etna without invoking rapid (< 1 min) low temperature oxidation processes. We further model Hg speciation for a series of additional magmatic gas compositions. Compared to Etna, Hg(II) production (i.e., Hg(II)/Hgtot) is enhanced in more HCl-rich magmatic gases, but is independent of the Hg, HBr and HI content of the magmatic gases. Hg(II) production is not strongly influenced by the initial oxidation state of magmatic gases above NNO, although production is hindered in more reduced magmatic gases. The model and results are widely applicable to other open-vent volcanoes and may be used to improve the accuracy of chemical kinetic models for low temperature Hg speciation in volcanic plumes.</p
