Proposition de stages, thèses et post-docs

Laboratoire de Physicochimie des Processus de Combustion et de l'Atmosphère
PC2A - UMR 8522 CNRS/Lille1
Université Lille 1 Sciences et Technologies
Cité scientifique, Bâtiment C11/C5
59655 Villeneuve d'Ascq Cedex, France

Le Laboratoire de Physicochimie des Processus de Combustion et de l'Atmosphère de l'Université Lille1 Sciences et Technologies cherche des physico-chimistes, chimistes ou physiciens de formation, pour préparer un stage de recherche Master (Année universitaire 2017-2018), une thèse de doctorat ou un Post-Doc dans le domaine de l'énergétique et de l'environnement de Septembre-Octobre 2017.

Les sujets de recherche proposés concernent les domaines de la combustion, de la sûreté nucléaire et de l'environnement. Ils s'inscrivent dans des axes de recherche soutenus par le Ministère de l'Enseignement Supérieur et de la Recherche, le CNRS-INSIS, l'Institut de Radioprotection et de Sûreté Nucléaire (IRSN) et le Contrat de Projet Etat-Région Nord Pas-de-Calais.

Les candidatures, comportant un CV et une lettre de motivation, doivent être soumises auprès des chercheurs responsables des sujets proposés.

Master 2

Kinetic study of reactions with interest to atmospheric and combustion chemistry by simultaneous detection of OH and RO2 radicals coupled to laser photolysis

OH radicals as well as peroxy radicals (HO2 and RO2) are key species not only in the atmospheric chemistry reaction mechanism, but also in combustion processes, two research domains that are developed in the laboratory PC2A. In this frame, we have set-up an experimental technique able to determine the concentrations of these radicals in a time resolved manner with the goal of studying kinetics of elementary reactions involving these radicals. The set-up is composed of a photolysis laser, initiating the reaction by a pulsed photolysis of an appropriate precursor in the reaction (i.e. H2O2 for generating OH radicals), coupled to two detection techniques:

- OH radicals by Laser Induced Fluorescence (LIF) at high repetition rate (10 kHz)

- Peroxy radicals by continuous wave Cavity Ring Down Spectroscopy (cw-CRDS) in the near IR

In the frame of the proposed PhD work, this experimental set-up will be used to study different reaction systems of atmospheric or combustion interest, for example:

- the degradation of isoprene, a biogenic volatile organic compound (VOC)emitted in large quantities by vegetation

- the cross reactions between HO2 and other RO2 radicals, a very important class of reaction in remote environment, only poorly understood. The simultaneous measurement of OH and HO2 / RO2 radicals will allow determining the branching ratios of such reactions.

Keywords: Peroxy radicals, OH radicals, laser photolysis, laser spectroscopy

Linked to the workpackage of the Labex CaPPA : WP 1

Supervisors: Christa Fittschen / Coralie Schoemaecker

 

Study of I2 interactions with inorganic aerosols using molecular modelling tools

Reactive halogen species are commonly known for their role in the ozone depletion in the stratosphere. They actually play an important role in tropospheric chemistry, especially in the polar and marine boundary layers. They impact the oxidative capacity of the troposphere via catalytic destruction of ozone or altering NO/NO2 and OH/HO2 cycles.

 

For the most common halogens such as chlorine and bromine, these reactions are pretty well known in gas phase and are included in simulation models. Although iodine species are a minor constituent of seawater, recent field studies have measured significant levels of organic and inorganic iodine in the marine boundary layer.

 

Another sources of discrepancies between experimentally observed concentrations and those calculated by simulation models is the lack of knowledge on heterogeneous processes of solid surfaces of aerosols with gas-phase molecular species.

 

In this context, the aim of this research project is to understand how molecular iodine behaves at the surface of aerosols found in the marine boundary layer (NaCl, sulphate, nitrate). For this work, ab initio molecular simulation will be performed using the Vienna Ab initio Simulation Package (VASP) after an initial training at the lab. The results obtained could help further experimental researches.

 

Keywords: aerosols, marine boundary layer, I2, molecular simulations

Linked to the workpackage of the Labex CaPPA : WP 6

Supervisors: Fayçal ALLOUTI / Florent LOUIS

Optical properties of aerosols measured in the IR and UV range

Because of their ability to absorb and to scatter radiations, airborne particles play an important role in the energy budget of the earth-atmosphere system. It is assumed that aerosols are one of the atmospheric constituents participating to the cooling effect, but estimates are highly uncertain owing to the large spatial and temporal variability of aerosol concentration and physical properties.

The measurements from space-borne instruments are the only means for observing aerosol distributions from local to global scale. However, to fully exploit the instruments capabilities it is essential to have reference optical properties of various particles and mainly their complex refractive indices.

The aim of this work is to measure transmittance spectra of model airborne particles in the infrared and the UV-vis spectral region using a dedicated experimental setup developed in PC2A. The extinction spectra of the aerosol are measured by Fourier Transform InfraRed (FTIR) spectrometer and UV-vis spectrometer and the corresponding size distributions are recorded using optical counters. The whole methodology has been validated using model silica particles and volcanic ashes. The team wants to extend this methodology to other particles of atmospheric interest, e.g., pure water droplets, water droplets containing bioaerosols or silica particles with water adsorbed on their surface. Thus the objective of the internship is to transform the set-up in order to generate such particles and to measure their optical properties in parallel with chemical composition and some physical properties such as the size and the concentration of the particles. The experimental data are then processed in order to retrieve the complex refractive indexes of these aerosols (collaboration with LOA).

                 

This project is addressed to physicist or chemist candidates, interested in the experimental aspects of the research and motivated by the atmospheric impact of aerosols.

                 

Keywords: atmospheric particles, metrology of the aerosol, FTIR and UV-vis spectroscopy

Workpackage of the Labex CaPPA: WP2

Supervisors: Denis Petitprez (PC2A) - Hervé Herbin (LOA) - Olivier Pujol (LOA)

Modelling iodine interactions with atmospheric aerosols

Following a severe nuclear power reactor accident, radionuclides like caesium and iodine are released into the atmosphere. Models could predict health impact and organize population evacuation if the need arises. The computer codes used by the IRSN in case of accidental release of radioactive products do not consider the dispersion and drawdown effects; the source term is chemically inert. However, the reactivity of iodine in the atmosphere is well known, and this hypothesis has to be reassessed.

During the Fukushima accident, the simulations have defined quantities of caesium relatively close to those measured in the field, this is not the case for iodine. This discrepancy could be explained by the chemical reactivity of iodine in the atmosphere, which is not implemented in the codes. Indeed, parameters like deposition velocity or the dose-effect factor depends on Iodine chemical speciation and physical form (gas, particle, liquid, solid). Therefore, heterogeneous reactions are important to evaluate the radiologic impact.

The purpose of this internship is to make a critical review of the literature to complete the iodine chemical mechanism with the heterogeneous reactions. 0D modelling studies will be conducted to evaluate the iodine species speciation under various atmospheric conditions (temperature, photolysis, gas and aerosols concentration, ...). The iodine reactivity will be added in heterogeneous phase to the chemical transport models (Chimere and Polair3D in our case) to have a better understanding of the Fukushima accident.

This project will be performed in the framework of the Laboratoire de Recherche Commun C3R (Cinétique Chimique, Combustion, Réactivité) IRSN/CNRS/Lille1 and the Labex CaPPA – WP6 (Chemical and Physical Properties of the Atmosphere).

 

Keywords:  Iodine, Chemistry-transport, Heterogeneous Reactivity, Fukushima

Linked to the workpackage of the Labex CaPPA : WP6

Supervisors: Valérie FEVRE-NOLLET / Patrick LEBEGUE

Biomarkers of Air Pollution on Pollen

Pollen grain has a brief atmospheric airborne life ranging from hours to days during pollination period. Pollen grain is modified by gaseous and particulate pollution during its transport in the atmosphere.

     The modifications of pollen grains by atmospheric pollution induce an inhibition of the germinative capability of the pollen, an increase of its allergenic potential and facilitate the dispersion of allergens in the fine fraction of atmospheric aerosols (1).

     Pollen lipidic fraction can be modified in laboratory conditions by air pollutants, particularly by ozone (2). With this internship, pollen will be exposed to oudoor atmospheric pollution in situ. The candidate will have to design suitable exposure conditions of pollen to outdoor pollution. The lipidic fraction of pollen will be used as a marker of pollution. Lidids will be extracted and analyzed by chromatographic techniques (GC-MS, GC-FID and HPLC).

     Rupture of pollen will also be studied by measuring size distributions with an Aerodynamic Particle Spectrometer (APS).

(1) Sénéchal, H. et al. A Review of the Effects of Major Atmospheric Pollutants on Pollen Grains, Pollen Content and Allergenicity. The Scientific World Journal 2015, ID 940243 (2015).

(2) Naas, O. et al. Chemical modification of coating of Pinus halepensis pollen by ozone exposure. Environmental Pollution 214, 816–821 (2016).

 

Keywords: Heterogeneous Chemistry, Analytical Chemistry, Allergy

Linked to the workpackage of the Labex CaPPA: WP 2

Supervisor: Nicolas Visez

Gas phase reactivity of iodine-containing species of atmospheric interest

The goal of this internship is to improve the understanding of the homogeneous reactivity of iodine-containing species with major photo-oxidants, to better address the lack of data in the field of atmospheric chemistry and nuclear safety, and to provide a set of reliable kinetic and mechanistic data on gas-phase iodine reactivity. These data will improve the relevance and accuracy of iodine dispersion models.

 

Quantum chemistry is more and more used to determine rate constants for gas-phase elementary reactions because the power of the current generation of computers allows to obtain reliable kinetic parameters. It permits to understand the mechanism of global and elementary reactions. It allows to calculate the molecular properties (geometrical data, molecular mass, vibrational frequencies, inertia moments) of reactants, products, transition states, and molecular complexes for an elementary reaction. Then, the macroscopic quantities such as the thermodynamical functions (internal energy, enthalpy, and Gibbs free energy) are calculated from molecular properties using statistical thermodynamics. Finally, temperature and pressure dependencies of rate constants are determined using kinetic theories from thermodynamical functions.

 

This project will be performed in the framework of the Laboratoire de Recherche Commun C3R (Cinétique Chimique, Combustion, Réactivité) IRSN/CNRS/Lille1 and the Labex CaPPA – WP6 (Chemical and Physical Properties of the Atmosphere). The subject of this research project can be pursued through a Ph-D.

 

Keywords: Iodine, theoretical chemistry, reactivity, kinetics, atmospheric chemistry, nuclear safety

Linked to the workpackage of the Labex CaPPA : WP6

Supervisor(s): Florent LOUIS / Marc RIBAUCOUR

Soil spreading of organic waste products: source of secondary organic aerosols?

Agricultural lands occupy about 40-50% of the Earth’s land surface. In order to assess the potential of agricultural ecosystems to act as a source or sink for ozone and volatile organic compounds (VOC), it is necessary to determine the emissions and deposition within the interface soil-atmosphere.

The valorisation of different types of organic waste products (OWP) from farms (cattle, pigs...), urban origin (sewage sludge, green waste) or industrial (sweets, etc.) is currently promoted as a substitute for mineral fertilizers. OWPs have a wide variety of characteristics due to their origin and the treatments that they may undergo before spreading and this diversity of characteristics could have a significant impact on gaseous emissions following soil application.

The agricultural soils emit volatile organic compound (VOC) that contribute to the formation of secondary pollutants such as ozone but also to the formation of secondary organic aerosols (SOA), both pollutants being under regulation.

The present project is focused in the study of SOA formation and ozone deposition and reactivity at the soil-atmosphere interface. Laboratory based measurements will investigate the related emissions of VOC from OWPs and their subsequent reaction with ozone to form aerosols. The experiments will be performed in an aerosol flow tube where the VOC will react with the ozone. An high panel of scientific equipment will be deployed and allow the physical and chemical characterisation of the VOCs and freshly formed aerosols (proton transfer mass spectrometer, scanning mobility particle sizer,…). Filter measurements of aerosols will allow their chemical and molecular characterisation by off-line analysis (gas chromatography, time of flight secondary ions mass spectrometry).The interested candidate will participate at the development of the experimental set-up and will perform experiments.

    

 This project is addressed to agronomist, physicist or chemist candidates interested in the experimental aspects of the research and motivated by the atmospheric impact of aerosols.

 

Labs: PC2A and INRA

Period: from February 1st 2017 to June 30 2017

Gratification: €554.40 per month

Keywords: volatile organic compounds, organic waste products, aerosols, mass spectrometry

Supervisors: RalucaCiuraru (INRA) and Denis Petitprez (PC2A)

 

 

 

Thèses

Analyse expérimentale de la phase gazeuse et particulaire en conditions de flamme: Identification des espèces clefs impliquées dans les processus de formation des suies

 

 

La formation des particules de suies dans les processus de combustion est une problématique de recherche majeure du fait de l’impact négatif de ces composés sur notre santé et notre environnement. Le lien entre l’ingestion de ces particules et certaines pathologies touchant principalement les voies respiratoires est en effet bien établi. La toxicité des particules de suie est principalement liée au fait que celles-ci peuvent transporter des composés cancérigènes adsorbés à leur surface. Outre leur effet délétère sur la santé humaine, il est aujourd’hui avéré que les particules de suie participent également au changement climatique à l’échelle de la planète. Elles sont mêmes selon une étude récente estimées comme étant le deuxième activateur de l’effet de serre juste derrière le dioxyde de carbone. Cette propriété leur est conférée par le pouvoir absorbant dont elle dispose vis-à-vis d’une partie du rayonnement solaire ainsi que de par leur propension à réfléchir une fraction du rayonnement infrarouge réémis par la Terre.

 

C'est pourquoi, la compréhension des mécanismes chimiques de formation de ces composés fait l'objet de nombreux travaux de recherche de par le monde. Cependant, de larges zones d'ombres demeurent sur ces mécanismes, notamment concernant la nature des réactions chimiques et des espèces gazeuses mises en jeu dans ces processus de formation. L'obtention de données expérimentales quantitatives fiables (profils de concentration d'espèces) est une étape cruciale pour aboutir à une compréhension fine des ces processus, qui requiert la mise en œuvre de techniques expérimentales sophistiquées et adaptées à l'étude de flammes. 

 

Le sujet de thèse que nous proposons vise à caractériser les principales espèces moléculaires impliquées dans les processus de formation des particules de suie. Pour ce faire, des dispositifs analytiques classiques comme la chromatographie en phase gaz (GC) ou la spectrométrie infrarouge par transformée de Fourier (IRTF) seront mises en œuvre pour la mesure des petites espèces gazeuses moléculaires. Ces mesures, qui requièrent le prélèvement des espèces de la flamme au moyen d'une microsonde, seront réalisées dans une flamme de diffusion de méthane cylindrique, laminaire et génératrice de particules de suies. La mesure de température, qui est une donnée essentielle pour le développement de modèles cinétique, sera obtenue par thermocouples Pt/Rh. Parallèlement à ces travaux, la mesure des HAPs (hydrocarbures aromatiques polycycliques) et des suies seront réalisées au moyen de techniques lasers innovantes. Les HAPs seront mesurés par fluorescence induite par laser en jet froid (JCLIF), qui est un dispositif original et particulièrement sensible pour la mesure de ces composés développée depuis plusieurs années au PC2A. Les particules de suie seront étudiées par incandescence induite par laser (LII). Des possibilités d'analyses supplémentaires réalisées au Synchrotron Soleil (Gif-sur-Yvette) sont également envisagées dans le cadre de cette thèse. La détermination de profils radiaux et axiaux (le long de la hauteur de la flamme) permettra l'obtention d'une véritable cartographie des espèces impliquées dans les processus de formation des particules. L'obtention de ces nouvelles données expérimentales constitue un élément très précieux, car il offre la possibilité d'évaluer les mécanismes chimiques détaillés dans des conditions plus réalistes que celles proposées par les flammes 1D prémélangées étudiées jusqu'ici.

 

Ce sujet de thèse s'adresse donc spécifiquement à des candidats chimistes ou physiciens à vocation clairement expérimentale et souhaitant acquérir des compétences dans les domaines de la chimie analytique et des diagnostics lasers.

 

Programmes de recherche en lien avec le sujet : CPER Climibio

 

Mots clés :   Particules fines - HAPs – Suie – Diagnostics Lasers – Chromatographie - Flamme

 

Responsables et coordonnées :

PC2A :                   Xavier Mercier                     xavier.mercier@univ-lille1.fr                                           03 20 43 48 04

PC2A :                   Abderrahman El Bakali     abderrahman.el-bakali @univ-lille1.fr                          03 20 43 48 04

 

 

Études cinétiques des réactions d’intérêt atmosphériques par détection simultanée des radicaux OH et RO2 couplé à la photolyse laser

 

Les radicaux OH ainsi que des radicaux peroxyles (HO2 et RO2) sont des espèces clés dans les mécanismes réactionnels en chimie de l’atmosphère mais également en combustion, deux domaines de recherches développés au laboratoire PC2A.  Dans ce cadre, nous avons mis en place un dispositif expérimental résolu dans le temps pour la mesure de ces radicaux afin d’étudier les cinétiques de réactions élémentaires. Il s’agit d’une cellule de photolyse laser, qui initie la réaction par photolyse pulsée d’un précurseur approprié (p.e. H2O2 pour faire le radical OH), couplée à trois moyen de détection : la Fluorescence Induite par Laser à haut cadence permet de détecter le radical OH d’une manière relative, deux voies de Cavity Ring Down Spectroscopy (CRDS) permet la quantification simultanée de deux espèces, par exemple HO2, OH (quantitatif), CH3O2, CH2O, H2O2…

 

Dans le cadre de cette thèse ce dispositif sera utilisé pour l’étude de différents systèmes d’intérêt atmosphérique, par exemple :

la réaction entre les radicaux RO2 et OH. Nous avons très récemment montré que ces réactions jouent un rôle important dans les atmosphères propres. Il est prévu d’étudier les réactions des radicaux RO2 issue des l’oxydation des COV biogénique.
les réactions entre le radical HO2 et d’autre radicaux peroxyle RO2, importantes aussi bien en atmosphère qu’en combustion basse température, peuvent mener aux produits stables (i.e. terminaison de la chaîne de réaction) ou à la formation des radicaux OH (i.e. continuation de la chaîne de réaction). La mesure simultanée et absolue de OH et RO2 / HO2 permet de déterminer le rapport de branchement entre ces deux voies.

 

Le candidat rechercher devra justifier d’une formation en chimie, physique ou physico-chimie avec de solides bases en spectroscopie, réactivité, optique atmosphérique.

 

Programmes de recherche en lien avec le sujet : LaBEX CaPPA, ClimiBio

 

Mots clés : Réactivité homogène – Chimie radicalaire – Photolyse laser – Spectroscopie

 

Responsables et coordonnées :

PC2A :                   Christa Fittschen                                christa.fittschen@univ-lille1.fr                         03 20 43 72 66

                               Coralie Schoemaecker     coralie.schoemaecker@univ-lille1.fr             03 20 43 72 66

 

Post-docs

Numerical study of the effect of additives to sooting premixed flames

Context and objectives

The PC2A laboratory has recently begun experimental and modeling studies on the influence of some additives on the sooting tendency in premixed laminar hydrocarbon flame conditions. The main objective is to control the impact of hydrogen and oxygenated molecules on both gas and particulate phase chemistry in a wide range of operating conditions (equivalence ratio, pressure and proportion of the additive).

On the experimental side, the laboratory has implemented various conventional (GC, GC/MS, IRTF) and diagnostic laser (LIF, LII, CRDS) techniques to cover a wide experimental data base constituted by:

  • Temperature profiles
  • Gaseous species mole fraction profiles including polycyclic aromatic hydrocarbons
  • Soot  volume fraction profiles
  • Distribution of the particle size

Numerically, the laboratory has the expertise to take advantage of the points i) and ii) for the development and validation of detailed phase gas mechanisms in flame conditions. Modeling data of iii) and iv) points is a recent topic in the laboratory. A recent soot code based on the sectional method has been developed and its association with our kinetic mechanisms has been successfully carried out using Cantera code. Our group wishes to recruit a postdoctoral researcher to support the development of this new theme. The person hired will support modeling soot volume fraction and particle-size distributions. The candidate is expected to be able to make the necessary improvements to the soot code such as taking into account the reversibility of some processes between the two phases.

Essential Requirements

Applicants will hold a Ph.D. degree in Chemical or Mechanical Engineering.

The position requires skills in:

  • Coding and software development skills (mainly C++/Python, other languages considered) in order to improve the existing sectional soot model implementation in Cantera;
  • Detailed soot modelling (sectional or moment methods, stochastic approaches)
  • Combustion chemistry and laminar 1D-flame simulations;

Application: For application, send a detailed CV which includes the list of publications, a covering letter and contact details to:

Abderrahman el Bakali           +33.3.20.43.49.30

Pascale Desgroux         +33.3.20.43.48.04

Salary: This work is supported by CPER CLIMIBIO (http://climibio.univ-lille.fr/). Month salary depends on candidate experience.