102 research outputs found
Etude de la source et du transport des aérosols marins en zone côtière méditerranéenne
The knowledge of both the source and atmospheric transport of marine aerosols is needed for a better understanding of a large number of physicochemical processes that control the lower troposphere properties. In this context, the present work deals with the modelization of the generation and atmospheric transport of marine aerosols in the Mediterranean coastal zone. In particular, this study allowed improvement of the aerosol transport model MACMod on the basis of a specific work on the boundary conditions. A new formulation of the sea-spray source function has been determined for the northern Mediterranean and effects of the transformations of the sea-spray particles during their atmospheric transport were identified. In addition, to better take into account the influence of the anthropogenic zones for the boundary conditions, the implementation of the CHIMERE model on the study area was made. Finally, a last part of the thesis was dedicated to the use of the MACMod model for the air quality forecasting and the survey of the PM2.5 and PM10 concentrations.La connaissance de la source et du transport atmosphérique de l’aérosol marin est primordiale pour mieux comprendre un grand nombre de processus physico-chimiques régissant les propriétés de la basse troposphère. C’est dans ce cadre que s’inscrit cette thèse dont l’objectif principal concerne la modélisation de la génération et du transport des aérosols marins en zone côtière Méditerranéenne. Cette étude a permis notamment l’amélioration du modèle de transport MACMod à partir d’un travail sur les conditions aux surfaces frontières. Une formulation de la fonction source spécifique à la région méditerranéenne nord-occidentale a été déterminée et certains effets des transformations subies par les particules issues de la production primaire au cours de leur transport atmosphérique ont été analysés. De plus, dans le but de mieux tenir compte du cas des zones anthropisées pour les conditions aux limites du modèle, un travail sur l’implémentation du code CHIMERE sur la région méditerranéenne a été initialisé. Enfin, une dernière partie a été consacrée à l’adaptation du modèle MACMod à la prévision de la qualité de l’air et le suivi des concentrations de PM2.5 et PM10
Fuel cell electrodes from organometallic Pt precursors: an easy atmospheric plasma approach
An organometallic powder (platinum (II) acetylacetonate) is decomposed in the
post-discharge of an atmospheric RF plasma torch to deposit Pt nanoparticles on
carbon black supports. The resulting nanohybrid materials are characterized by
FEG-SEM and XPS techniques to highlight their high content in Pt, their
oxidation degree, and the dispersion of the Pt nanoparticles on the substrate.
ICP-MS and electrochemical characterizations in a single fuel cell (cyclic
voltammetry, dynamic polarization curves) are also performed on electrodes
realized by treating the powder mixture overlaid on gas diffusion layers. The
comparison of the catalytic activity and the Pt loading with commercially
available electrodes shows the great potential of this simple innovative, fast,
and robust deposition method
Réactivité aux échelles micronique et submicronique de particules colloïdales : oxydation d'un sulfure de fer (pyrite) par du chrome (VI) et sorption sur un hydroxyde d'aluminium (gibbsite) d'espèces organiques
Two systems characterised by oxydoreduction and sorption of surface reactions are studied: the pyrite oxidation (FeS2) by chromium (VI) and the sorption of dinitro-2,4 benzoic species on gibbsite (g-Al(OH)3). The aim of the first system is to study the pyrite oxidation processes of the pyrite by using chromium (VI) like a metal probe. The solution analysis by UV-visible spectroscopy and the solid phase characterisation by confocal Raman spectrometry, XPS, EXAFS and XANES allow to suggest a mechanism model of oxidation/dissolution. The objective of the second study is to display a specific chemical reactivity between two crystalline face types of the gibbsite by using an organic probe with the help of sub-wavelength spectroscopy (SNOM). Correlations between crystalline faces and near field spectra show difference reactivity between mono and bi coordinated OH groups from the mineral phase. A model of sorption is presented.Deux systèmes à pouvoir d'oxydoréduction et de sorption de surface sont étudiés : l'oxydation de pyrite (FeS2) par du chrome (VI) et l'adsorption d'espèces 2,4-dinitrobenzoate sur gibbsite (g-Al(OH)3). L'enjeu du premier système est d'appréhender le processus d'oxydation de la pyrite en utilisant une sonde métallique, le chrome (VI). L'analyse de la solution par spectroscopie UV-visible et la caractérisation de la phase solide par spectrométries Raman confocal, XPS, EXAFS et XANES permettent de proposer un modèle de mécanisme d'oxydation/dissolution. L'objectif de la seconde étude est de mettre en évidence une différence de réactivité de surface entre deux types de face cristalline de la gibbsite à l'aide d'une sonde organique en utilisant la spectroscopie optique en champ proche (SNOM). Les corrélations faces cristallines/spectres en champ proche indiquent une réactivité différente entre les hydroxyles mono et bi-coordonnées de la phase minérale. Un modèle de sorption est présenté
Study of the source and the transport of Sea-spays in the Mediterranean Coastal Zone
La connaissance de la source et du transport atmosphérique de l’aérosol marin est primordiale pour mieux comprendre un grand nombre de processus physico-chimiques régissant les propriétés de la basse troposphère. C’est dans ce cadre que s’inscrit cette thèse dont l’objectif principal concerne la modélisation de la génération et du transport des aérosols marins en zone côtière Méditerranéenne. Cette étude a permis notamment l’amélioration du modèle de transport MACMod à partir d’un travail sur les conditions aux surfaces frontières. Une formulation de la fonction source spécifique à la région méditerranéenne nord-occidentale a été déterminée et certains effets des transformations subies par les particules issues de la production primaire au cours de leur transport atmosphérique ont été analysés. De plus, dans le but de mieux tenir compte du cas des zones anthropisées pour les conditions aux limites du modèle, un travail sur l’implémentation du code CHIMERE sur la région méditerranéenne a été initialisé. Enfin, une dernière partie a été consacrée à l’adaptation du modèle MACMod à la prévision de la qualité de l’air et le suivi des concentrations de PM2.5 et PM10.The knowledge of both the source and atmospheric transport of marine aerosols is needed for a better understanding of a large number of physicochemical processes that control the lower troposphere properties. In this context, the present work deals with the modelization of the generation and atmospheric transport of marine aerosols in the Mediterranean coastal zone. In particular, this study allowed improvement of the aerosol transport model MACMod on the basis of a specific work on the boundary conditions. A new formulation of the sea-spray source function has been determined for the northern Mediterranean and effects of the transformations of the sea-spray particles during their atmospheric transport were identified. In addition, to better take into account the influence of the anthropogenic zones for the boundary conditions, the implementation of the CHIMERE model on the study area was made. Finally, a last part of the thesis was dedicated to the use of the MACMod model for the air quality forecasting and the survey of the PM2.5 and PM10 concentrations
Réactivité aux échelles micronique et submicronique de particules colloïdales (oxydation d'un sulfure de fer (pyrite) par du chrome (VI) et sorption sur un hydroxyde d'aluminium (gibbsite) d'espèces organiques)
Deux systèmes à pouvoir d'oxydoréduction et de sorption de surface sont étudiés : l'oxydation de pyrite (FeS2) par du chrome (VI) et l'adsorption d'espèces 2,4-dinitrobenzoate sur gibbsite (g-Al(OH)3). L'enjeu du premier système est d'appréhender le processus d'oxydation de la pyrite en utilisant une sonde métallique, le chrome (VI). L'analyse de la solution par spectroscopie UV-visible et la caractérisation de la phase solide par spectrométries Raman confocal, XPS, EXAFS et XANES permettent de proposer un modèle de mécanisme d'oxydation/dissolution. L'objectif de la seconde étude est de mettre en évidence une différence de réactivité de surface entre deux types de face cristalline de la gibbsite à l'aide d'une sonde organique en utilisant la spectroscopie optique en champ proche (SNOM). Les corrélations faces cristallines/spectres en champ proche indiquent une réactivité différente entre les hydroxyles mono et bi-coordonnées de la phase minérale. Un modèle de sorption est présenté.Two systems characterised by oxydoreduction and sorption of surface reactions are studied: the pyrite oxidation (FeS2) by chromium (VI) and the sorption of dinitro-2,4 benzoic species on gibbsite (g-Al(OH)3). The aim of the first system is to study the pyrite oxidation processes of the pyrite by using chromium (VI) like a metal probe. The solution analysis by UV-visible spectroscopy and the solid phase characterisation by confocal Raman spectrometry, XPS, EXAFS and XANES allow to suggest a mechanism model of oxidation/dissolution. The objective of the second study is to display a specific chemical reactivity between two crystalline face types of the gibbsite by using an organic probe with the help of sub-wavelength spectroscopy (SNOM). Correlations between crystalline faces and near field spectra show difference reactivity between mono and bi coordinated OH groups from the mineral phase. A model of sorption is presented.NANCY1-SCD Sciences & Techniques (545782101) / SudocSudocFranceF
Pyrite oxidation in acidic medium: Overall reaction pathway
This study investigated the oxidation processes of pyrite by dissolved oxygen. Synthetic pyrite suspensions have reacted with dissolved oxygen in a closed-thermostated system for 20 h and at pH values of 2.0 and 3.5. Special emphasis was made on the characterization of the solid phase formed during the reaction process, using X-ray photoelectron spectroscopy (XPS) and confocal Raman microspectrometry. The results revealed a strong heterogeneity of the samples with the identification of two different micrometric areas. E g and Ag Raman pyrite modes were characterized by wavenumber drifts, from 0 to 6, correlated with the shine changes of the micrometric probed area. XPS analyses provided evidence of the distribution of iron and sulfur species at the reacted pyrite surface. The Fe(2p3/2) signals showed an increase in the binding energy range typical of Fe(III)-S and Fe(III)-O compounds. The S(2p) XPS signals included contribution from disulfide, monosulfide, elemental sulfur, and sulfate. Elemental sulfur should be protected from sublimation under ultrahigh vacuum, possibly by an overlaying of other species such as Fe(III) (oxyhydr)oxide species. An overall reaction pathway of the pyrite in oxidizing (Cr(VI), dissolved oxygen, Fe(III)), and acidic media (pH ≤ 3.5) has been established from the present results and previous papers. Copyright © 2008 John Wiley & Sons, Ltd.SCOPUS: cp.jFLWINinfo:eu-repo/semantics/publishe
Investigation of pyrite oxidation by hexavalent chromium: Solution species and surface chemistry
International audiencePyrite oxidation processes by aqueous Cr(VI) were investigated at 25 °C under an argon atmosphere. Synthetic pyrite suspensions (6 g L−1) were reacted for 20 h with a range of Cr(VI) solutions from 0 to 700 μM and at pH 2–12. The main objective of this work was to investigate the reaction mechanisms by emphasizing the role of sulfur species. Aqueous chemical processes were well illustrated in acidic media where significant amounts of sulfate and iron species were determined. Sulfate anions are the final stable sulfur species involved in the reaction pathway. Experiments showing complete Cr(VI) removal from solution displayed ratios [S(VI)]/[Fe]tot < 2, probably due to a deficit in aqueous sulfur species. Experiments showing incomplete Cr(VI) removal displayed ratios [Cr(VI)]removed/[S(VI)] close to 1.5. This ratio was found to be consistent with the formation of thiosulfate (S2O2−3). Thiosulfate ions disproportionated into elemental sulfur S(0) and tetrathionate ions (S4O2−6) that were finally oxidized to sulfate anions under acidic conditions. The distribution of the oxidation state of sulfur atoms at the pyrite surface determined by XPS was additional evidence for the multistep sulfur oxidation process. The presence of elemental sulfur in the S(2p) spectra correlated well with the disproportion of thiosulfate under acidic conditions
A model for the atmospheric transport of sea-salt particles in coastal areas
The presnt paper deals with the latter development of the MACMod model dedicated to the aerosol transport. In particular,. a new formulation for the sea-spray source function is validated
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