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 2018-2019), une thèse de doctorat (à partir d'Octobre 2019), ou un Post-Doc dans le domaine de l'énergétique et de l'environnement.
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 Hauts de France.
Les candidatures, comportant un CV et une lettre de motivation, doivent être soumises auprès des chercheurs responsables des sujets proposés.
Role of the resonantly stabilized radicals in the inception of soot particles
Fossil fuel combustion constitutes the principal source of our energy needs. This combustion is unfortunately also the main source of the air pollution. Among the pollutants emitted by fuel combustion, there are polycyclic aromatic hydrocarbons (PAHs) of which we have a solid conviction that some of them are strongly harmful for health: there are indeed toxicological studies, which show their cancerogenic character. In addition, many studies carried out on the comprehension of the processes involving during PAHs and soot formation, agree on the implication of PAHs as precursors of soot particles. Soot particles are also very harmful for human being, more particularly the small particle sizes, which have a strong capacity of penetration in the lungs.
This training course lies within the scope of the continuation of the development and the validation of a detailed kinetic mechanism of hydrocarbon oxidation under rich fuel conditions producing soot particles. It aims to identify the impact of the resonantly stabilized radicals in the formation of the first aromatic rings. A particular attention will be paid to small PAHs (up 4-5 rings) as pyrene and its isomers, which are considered as direct precursors of nucleation soot process. It is expected to carry out quantum chemistry calculations by using chemical tools as Gaussian16. This work should confirm/cancel certain literature thermokinetic data, or to generate new data.
Keywords: PAHs, soot, combustion, detailed kinetic reaction mechanism, Flames, Quantum Calculations.
Linked to the workpackage of the Labex CaPPA : WP2
Optical properties of aerosols measured in the 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. water droplets containing bioaerosols or silica particles with water adsorbed on their surface. Reactivity with OH radicals will be also considered in order to estimate the role of atmospheric aging on the optical properties of the aerosols. 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 chemist or physicist 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
Supervisor: Denis Petitprez (PC2A) – Co-supervisor : Hervé Herbin (LOA)
Atmospheric chlorine chemistry modelling
The atmosphere is a complex chemical reactor in which a great number of reactions occurs. Most of these reactions are initiated by solar radiation and involves also chemical species either from natural or from anthropogenic sources. Although these compounds are present at very low level of concentration in the atmosphere (ppt to ppm), they could affect the environment and the climate. Human activities have noticeably changed the chemical composition of the atmosphere leading to the outcome of environmental problems such as global warming, or ozone depletion.
The reactions involving chlorine-containing species can modify the chemistry and the composition of the atmosphere. It stills however a lot of uncertainties in the understanding of the gas-phase atmospheric chemistry of these compounds.
The goal of this internship is to improve the understanding of the gas-phase reactivity of chlorine-containing species, to better address the lack of data in the field of atmospheric chemistry and to make a critical review of the literature to establish the chlorine chemical mechanism. 0D modelling studies will be conducted to evaluate the chlorine species speciation under various atmospheric conditions (temperature, photolysis, gas concentration, ...).
Keywords: Atmosphere, chlorine, chemical mechanism, 0D modelling
Linked to the workpackage of the Labex CaPPA : WP6
Low-cost aerosol counters in a volcanic environment
The populations of aerosols are more and more studied because they present a very great diversity of chemical compositions, origins and distributions in sizes (oceanic, industrial, biogenic, volcanic, etc.). This wealth leads to multiple effects, that can be negative or positive, on the evolution of the Earth system and its biosphere: impact on climate, chemical balance (desert and marine aerosols) and imbalance (anthropogenic pollution) of ecosystems, pollen and human health problems, for instance. These impacts can be revealed at different scales (from indoor pollution to climate impact). It results in an interest in a wide range of instrumentation for the study and monitoring of aerosol populations at different scales from satellites to local in situ measurements.
Low-cost particle counters are now available and pave the way for in situ real-time mapping of aerosol populations. These sensors can easily be integrated, embedded and deployed in a network to probe hostile environments like a volcano, or an area with complicated topography such as a subway network. These small instruments are however much less efficient than the research instruments used in the laboratories, and characterization of their response to a given environment is necessary. In the framework of anemerging collaboration between LACy (University of La Reunion), LASIR (University of Lille) and PC2A (University of Lille), we propose an internship on the conditions of use of this instrumentation for the study of aerosols in the volcanic and oceanic environment of La Réunion island: the Optical Particle Counter OPCN3 (Alphasense company) counts particles in the range 350 nm - 40 µm in 24 channels and weights 100g. The Grimm MiniWRAS 1371 countsparticles in the range 10 nm - 35 µm in 41 channels and weights 7 kg. Thus, they allow to probe the kinetic of the Aitken and coagulation/accumulation modes. The internship will consist in working in the PC2A laboratory on the response of these sensors in a controlled atmosphere and then deploying the sensors during a campaign on the Piton de la Fournaise. The data will then be analyzed by combining routine aerosol measurements at the Reunion Island Atmosphere Physics Observatory (OPAR) located a few tens of kilometers from the volcano.
Keywords: Low-cost particle counter, sensor answer, natural aerosols, volcano, data science
Laboratories:LACy (Laboratoire de l’Atmosphère et des Cyclones) ; PC2A (laboratoire de Physicochimie des Processus de Combustion et de l'Atmosphère) ; LASIR (Laboratoire de Spectrochimie Infra-rouge et Raman) ; LOA (Laboratoire d’optique Atmosphérique)
Linked to the workpackage of the LabexCaPPA:WP 3
Unravelling the gas-phase atmospheric iodine reactivity using molecular simulations
The goal of this internship is to improve the understanding of the homogeneous reactivity of iodinated species with major photo-oxidants. It will provide a set of reliable kinetic and mechanistic data on gas-phase iodine reactions of atmospheric interest.
Theoretical chemistry is more and more used to determine rate constants for elementary reactions in the gas phase. In fact, the power of the actual computers allows now to obtain quantitative kinetic parameters within chemical accuracy. Quantum chemistry permits to understand the mechanism of the global reaction and of the different elementary pathways. It also allows to compute the molecular properties (molecular mass, vibrational frequencies, inertia moments) for the reactants, products, transition states, and molecular complexes. Then, the macroscopic properties such as the thermodynamical functions (internal energy, enthalpy, and Gibbs free energy) are computed from molecular properties using statistical thermodynamics. Finally, temperature and pressure dependencies of rate constants are estimated with kinetic theories using with the previously determined thermodynamical functions.
Keywords: Iodine, theoretical chemistry, reactivity, kinetics, atmospheric chemistry
Linked to the workpackage of the Labex CaPPA : WP6
Measurements of Polycyclic Aromatic Hydrocarbons and Oxygenated Polycyclic Aromatic Hydrocarbons in the combustion of advanced biofuels.
Biofuels are considered as promising sources for renewable energy production, which reduces the net CO2 emissions and the fossil fuel dependency. Combustion process is the mostly-used way to produce energy from fuels (>80% of the world’s primary energy supply is currently produced throughout combustion process; such process can be seen in flame burners, car engines, airplane engines, etc.). Recent studies have shown that the combustion of oxygenated biofuels produces lower amounts of large-sized soot particles (>10 nm) than conventional petroleum fuels. However, the biofuels potentially generate higher amounts of small-sized soot particles (<10 nm) and these particles contain a significant fraction of oxygenates including oxygenated polycyclic aromatic hydrocarbons (OPAHs) which are generally more toxic than polycyclic aromatic hydrocarbons (PAHs). These small-sized particles can penetrate deep into lungs and become very harmful for the health.
Due to the presence of oxygen atoms in the chemical structure of biofuels, the chemical species distribution and reaction mechanisms in the soot formation processes are expected to be much more complex compared to conventional fuels. Understanding the formation mechanism of these particles is therefore very challenging, but it is a prerequisite step towards developing cleaner combustion technologies of biofuels. PAHs have been proven to be the origin of soot formation, while the role of OPAHs in soot formation processes is less understood and will be explored in this internship. Concretely, the master student will identify and quantify PAHs and OPAHs in a premixed flame of fuel/biofuel mixture using gas chromatography (GC) instruments. These instruments are equipped with different columns, different detectors (thermal conductivity detector, flame ionization detector, a mass spectrometric detector), and a special system for trapping PAHs/OPAHs. The expected results will serve to analyze the relationship between OPAHs and PAHs, and their kinetic formation, which will provide a solid base for developing a longer-term proposal on the formation mechanism of small-sized soot particles in the combustion of biofuels.
Keywords: Biofuels, soot, PAHs, OPAHs, GC
Linked to the workpackage of the Labex CaPPA: WP 5
Theoretical study of the atmospheric reactivity of iodinated compounds
Chemical reactions associated with atmospheric iodine have attracted increasing attention of experimentalists and theoreticians in recent years. The role of iodine in tropospheric chemistry has been documented in a number of papers over the last four decades, showing that both inorganic and organic species are emitted from the Marine Boundary Layer (MBL). While inorganic emissions of HOI and I2 account for the main source of iodine in the MBL, organic compounds include methyl, ethyl, and propyl iodide (CH3I, C2H5I, C3H7I) together with diiodomethane (CH2I2). Among them, CH3I is viewed as the dominant species with the highest mixing ratio and longest atmospheric lifetime. Rate coefficient data for reaction of OH with iodoalkanes have been experimentally determined for a series of alkyl iodides (CH3I, C2H5I, 1-C3H7I, and 2-C3H7I) as well as for CH2I2. Following their emission in the atmosphere, inorganic and organic iodine will be subject to photolysis under UV−visible light and quickly release I atoms, which play an active role in ozone destruction.
Gas-phase chemistry of iodine containing species is complex and studying its reactivity is challenging. The goal of this thesis is to improve the understanding of the homogeneous reactivity of iodine-containing species with major atmospheric photo-oxidants using theoretical approaches. This work is associated with the activities, which are already supported by the PIA Labex CaPPA (Chemical and Physical Properties of the Atmosphere, ANR-11-LABX-0005-01) in the work package 6 entitled "Hazard: dispersion, reactivity, deposition of radionuclides".
Theoretical chemistry is increasingly used to determine rate constants for elementary reactions in the gas phase. In fact, the power of the actual computers allows now to obtain quantitative kinetic parameters within chemical accuracy (± 4.18 kJ mol-1). Quantum chemistry permits to understand the mechanism of the global reaction and of the different elementary pathways. It also allows to compute the molecular properties (molecular mass, vibrational frequencies, inertia moments) for the reactants, products, transition states, and molecular complexes in the ground and excited states. Then, the macroscopic properties such as the thermodynamical functions (internal energy, enthalpy, entropy, and Gibbs free energy) are computed from molecular properties using statistical thermodynamics. Finally, temperature and pressure (fall-off behaviour and high-pressure limit) dependencies of rate constants are estimated with kinetic theories (such as the Transition State Theory (TST) or Rice-Ramsperger-Kassel-Marcus (RRKM) theory) using with the previously determined thermodynamical functions. This computational procedure has been already used at the PC2A laboratory for reactions involving iodinated compounds
Programmes de recherche en lien avec le sujet : Labex CAPPA
Mots clés : Iodine, atmosphere, molecular simulations
Responsables et coordonnées :
Florent Louis email@example.com Tel : 03 20 33 63 32
Financement envisagé : Bourse Conacyt (Mexique)
Unravelling the atmospheric iodine chemistry using molecular simulations in case of nuclear accident of a nuclear facility
The goal is to improve the understanding of the heterogeneous reactivity between gaseous iodinated species and aerosols present in the troposphere. To date, these heterogeneous interactions have not been considered in the atmospheric iodine dispersion models in case of a severe nuclear power plant accident. This is worrisome since such heterogeneous reactivity may play a major role in the iodine transport far from their emission sources. The importance of iodine in atmospheric chemistry has been highlighted by recent reviews. However, the atmospheric iodine heterogeneous reactivity studies have focused almost exclusively on determining the uptake coefficient of inorganic iodinated compounds (for example, I2, HI, and HOI) by water or ice. Those conditions are not fully relevant for our applications and have to be extended. Furthermore, photo-oxidation of gaseous CH3I and I2 in presence of O3 is known to produce IxOy aerosols, which are measured in the field campaigns. To the best of our knowledge, the influence of aerosols on the iodine photolysis processes in gas phase is not documented. Finally, the field measurements in Arctic and Antarctica pointed out the role of the low temperature in iodine chemistry in gas phase and in the formation of iodine-rich aerosols.
As a result, this thesis will provide a set of reliable kinetic and mechanistic data on iodine (photo)reactivity with atmospheric aerosols in order to improve the relevance and accuracy of iodine chemistry in dispersion models. The work will be based on molecular simulations; systems associating both the main iodinated gaseous species and representative atmospheric aerosols will be carefully selected.
Both molecular iodine (I2) and iodomethane (CH3I) are key iodine compounds of marine and biogenic origin that appears to be of central importance in understanding iodine chemistry in the troposphere. Further, in addition to their atmospheric interest, the reactivity of those compounds has gained much interest in the field of nuclear safety as they are the most probable gaseous iodine species to be released to the troposphere during a severe nuclear power plant accident of the type in Fukushima, Japan. As a result, this work will start on gaseous molecular iodine and iodomethane surface reactivity as a function of key inorganic and organic aerosols classes from the nanometric up to micrometric size. Model primary and secondary aerosols from marine origin will be considered, such as sodium chloride, sulphate, nitrate, and low to high oxidized organic aerosols.
Programmes de recherche en lien avec le sujet : Labex CAPPA
Mots clés : Iodine, aerosols, atmosphere, nuclear power plant, molecular simulations
Responsables et coordonnées :
PC2A : Florent Louis firstname.lastname@example.org Tel : 03 20 33 63 32
PhLAM Céline Toubin email@example.com Tel : 03 20 43 43 80
Financement envisagé : AAP I-SITE Sustain 2018 / Labex CaPPA (IRSN + PC2A + PhLAM)