Publications

2007

• Technical Note: The air quality modeling system Polyphemus
  
  • Mallet Vivien
  • Quélo D.
  • Sportisse B.
  • Ahmed de Biasi M.
  • Korsakissok I.
  • Debry Edouard
  • Wu L.
  • Roustan Y.
  • Sartelet K.
  • Tombette M.
  • Foudhil H.
  Atmospheric Chemistry and Physics, European Geosciences Union, 2007, 7 (20), pp.5479-5487. Polyphemus is an air quality modeling platform which aims at covering the scope and the abilities of modern air quality systems. It deals with applications from local scale to continental scale, using two Gaussian models and two Eulerian models. It manages passive tracers, radioactive decay, photochemistry and aerosol dynamics. The structure of the system includes four independent levels with data management, physical parameterizations, numerical solvers and high-level methods such as data assimilation. This enables sensitivity and uncertainty analysis, primarily through multimodel approaches. On top of the models, drivers implement advanced methods such as model coupling or data assimilation. (10.5194/acp-7-5479-2007)
  DOI : 10.5194/acp-7-5479-2007
• Aerosol modeling at regional scale: Model-to-data comparison and sensitivity analysis over Greater Paris
  
  • Tombette Marilyne
  • Sportisse Bruno
  Atmospheric Environment, Elsevier, 2007, 41 (33), pp.6941-6950. The aim of this paper is to present preliminary results of aerosol modeling over Greater Paris. We briefly describe the parameterizations and the numerical methods related to the general dynamic equation for aerosols: a size resolved aerosol model (SIREAM) has been hosted by the chemistry transport model Polair3D inside the Polyphemus system. Then the results of a simulation over Greater Paris are presented with preliminary comparisons to measured data for aerosols (PM10 and PM2.5) and gases (ozone, NO2) for six months of 2001 (from April to the end of September). A sensitivity analysis is also performed in order to assess the robustness of the model configuration. (10.1016/j.atmosenv.2006.10.037)
  DOI : 10.1016/j.atmosenv.2006.10.037
• Fast and stable vector spline method for fluid apparent motion estimation
  
  • Isambert Till
  • Herlin Isabelle
  • Berroir Jean-Paul
  , 2007, 6, pp.505-508. Apparent motion estimated on satellite data is used for example to compute the wind field in meteorology, and surface currents in oceanography. The satellite images display turbulent fluids with strong rotational patterns at different spatial and temporal scales. This specificity necessitates devising adapted methods, allowing to control the divergence and curl of the retrieved motion field. Vector spline methods are very adapted to that purpose. The vector spline problem is defined as finding a motion field that satisfies a temporal conservation equation at selected control points and that minimizes a regularity constraint in all the image domain. An exact solution of this problem can be found for the 2nd order div-curl regularity constraint. The retrieval of the solution does not require an iterative minimization procedure: a dense matrix must be inverted to compute the spline's coefficients. This matrix unfortunately becomes large and ill-conditioned as the number of control points increases, making the vector spline approach unsuitable for processing large satellite images. This paper presents a method called "Partition of Unity and Optical Flow'' (PUOF), based on a decomposition of the spatial domain: local vector splines are computed in subdomains of the image, then merged using a partition of unity algorithm. The resulting motion field is a good approximation of the exact vector spline solution, and its retrieval is numerically stable and computationally affordable even when processing large data sets, as demonstrated by results obtained on sequences of synthetic and meteorological images. (10.1109/ICIP.2007.4379203)
  DOI : 10.1109/ICIP.2007.4379203
• Estimation de vitesses par assimilation de données variationnelle
  
  • Huot Etienne
  • Xu Yann
  • Korotaev Gennady K.
  • Wu Lin
  • Herlin Isabelle
  • Le Dimet François-Xavier
  , 2007, pp.1285-1288. Les méthodes classiques d'estimation dense de la vitesse (de type flot optique) s'appuient sur l'estimation des dérivées spatio-temporelles de l'image. Celles-ci sont difficiles à estimer dans le cas d'occlusion d'une partie des acquisitions. Les approches issues de l'assimilation de données s'appuient sur un modèle d'évolution temporelle, qui permet de répondre à ce problème des données manquantes. Nous proposons donc une nouvelle approche pour estimer un champ de vitesse apparent, à partir d'une séquence d'images, en utilisant une méthode d'assimilation de données variationnelle. Pour cela un Modèle Image est construit, dans lequel sont assimilées les observations de la séquence d'images. Cette approche permet une estimation optimale de la vitesse, même si les observations sont partiellement manquantes comme c'est fréquemment le cas en imagerie satellite.
• Impact of mass consistency errors for atmospheric dispersion
  
  • Sportisse Bruno
  • Quélo Denis
  • Mallet Vivien
  Atmospheric Environment, Elsevier, 2007, 41 (29), pp.6132-6142. Atmospheric dispersion models are usually off-line coupled to mesoscale meteorological models. This may generate the loss of mass consistency, defined as the conservation of uniform mixing ratio. We investigate in this short paper the impact of the resulting mass consistency errors. Three methods based on the renormalization of density, on fluxes computed with mass mixing ratio and on the adjustment of the vertical velocity, respectively, are aimed at reducing the mass consistency errors. They are benchmarked and applied to two test cases: air quality modeling over Europe for summer 2001 (typical of reactive dispersion) and simulation of the Chernobyl accident (typical of passive dispersion). Our tests indicate the differences between the passive and the reactive cases. The investigation of the spatial patterns (especially of the vertical distribution) discriminates the method based on the adjustment of the vertical velocity. Indeed, this method suffers from the enhancement of the numerical diffusion (illustrated in the passive case) and from the modification of the escape flux (for ozone). (10.1016/j.atmosenv.2007.04.029)
  DOI : 10.1016/j.atmosenv.2007.04.029
• Simulation of aerosols and gas-phase species over Europe with the POLYPHEMUS system: Part I - Model-to-data comparison for 2001
  
  • Sartelet Karine
  • Debry Edouard
  • Fahey K.
  • Tombette Marilyne
  • Roustan Yelva
  • Sportisse Bruno
  Atmospheric Environment, Elsevier, 2007, 41 (29), pp.6116-6131. This paper aims at presenting a validation of multi-pollutants over Europe with a focus on aerosols. Chemistry-Transport Models are now used for forecast and emission reduction studies not only for gas-phase species but also for aerosols. Comprehensive model-to-data comparisons are therefore required. We present in this paper a preliminary validation study of the Polyphemus system applied over Europe for 2001. The aerosol model is the SIze REsolved Aerosol Model (SIREAM). It is a sectional model that describes the temporal evolution of the size/composition distribution of atmospheric particles containing a mix of black carbon, mineral dust, inorganic species, and primary and secondary organics. In addition to a brief model description, we present an overview of the model validation. A comprehensive set of model-to-data statistics is computed with observational data extracted from three European databases (the EMEP, AirBase and BDQA databases). Model performance criteria are verified for ozone and particulate matter (PM) and its inorganic components. Comparisons of correlations and root mean square errors with those generated by other models run over Europe for 2001 indicate a good performance of the Polyphemus system. Modifications of the system configuration and parameterizations may have a significant impact on error statistics, which may question the robustness of such models. Because large differences exist between databases, the robustness of model-to-data error statistics is also investigated. (10.1016/j.atmosenv.2007.04.024)
  DOI : 10.1016/j.atmosenv.2007.04.024
• Solving aerosol coagulation with size-binning methods
  
  • Debry Edouard
  • Sportisse Bruno
  Applied Numerical Mathematics: an IMACS journal, Elsevier, 2007, 57 (9), pp.1008-1020. The sectional approach is usually advocated for solving coagulation of atmospheric aerosols. This article aims at reviewing and benchmarking some widely used sectional methods. A rigorous framework is proposed and the focus is put on differences and similarities among the approaches. The sensitivity with respect to the computation of the partition coefficients is investigated. The dynamical behavior of coagulation is also studied. (10.1016/j.apnum.2006.09.007)
  DOI : 10.1016/j.apnum.2006.09.007
• Investigation of some numerical issues in a chemistry-transport model: Gas-phase simulations
  
  • Mallet Vivien
  • Pourchet Adélaïde
  • Quélo Denis
  • Sportisse Bruno
  Journal of Geophysical Research, American Geophysical Union, 2007, 112 (D15301). Many numerical strategies have been specifically developed for chemistry-transport models. Since no exact solutions are available for 3-D real problems, there are only few insights to choose between alternative numerical schemes and approximations, or to estimate the performance discrepancy between two approaches. However it is possible to assess the importance of numerical approximations through the comparison of different strategies. We estimated the impact of several numerical schemes for advection, diffusion and stiff chemistry. We also addressed operator splitting with different methods and operator orders. The study is performed with a gas-phase Eulerian model from the modeling platform Polyphemus. It is applied to ozone forecasts mainly over Europe, with focus on a few key species: ozone, nitric oxide, nitrogen dioxide, sulfur dioxide and hydroxy radical. The outcome is a ranking of the most sensitive numerical choices. It stresses the prominent impact of the advection scheme and of the splitting time step. (10.1029/2006JD008373)
  DOI : 10.1029/2006JD008373
• Validation of the Polyphemus platform on the ETEX, Chernobyl and Algeciras cases
  
  • Quélo Denis
  • Krysta Monika
  • Bocquet Marc
  • Isnard Olivier
  • Minier Yannick
  • Sportisse B.
  Atmospheric Environment, Elsevier, 2007, 41 (26), pp.5300-5315. The objective of this article is to investigate the validity of a modeling system developed for forecasting atmospheric dispersion, the POLYPHEMUS platform, with a special focus on radionuclides. The platform is briefly described and model-to-date comparisons are reported for three cases: the ETEX campaign, the Chernobyl accident and the Algeciras release. The results are similar to those usually given in the literature by state-of-the-art models. Some preliminary sensitivity analysis indicate the main sources for uncertainties. (10.1016/j.atmosenv.2007.02.035)
  DOI : 10.1016/j.atmosenv.2007.02.035
• Numerical simulation of the general dynamic equation (GDE) for aerosols with two collocation methods
  
  • Debry Edouard
  • Sportisse Bruno
  Applied Numerical Mathematics: an IMACS journal, Elsevier, 2007, 57 (8), pp.885-898. This paper presents two algorithms for solving the general dynamic equation for aerosols. Coagulation and condensation are solved simultaneously without using splitting. The first method is based on a collocation method for size discretization and a Rosenbrock solver for time integration. In the second method, time discretization is first performed. This leads to a Volterra equation of first kind, which is solved with cubic splines. Both methods are compared to a reference solution for constant coagulation and linear condensation. (10.1016/j.apnum.2006.08.002)
  DOI : 10.1016/j.apnum.2006.08.002
• Numerical Simulations of Reactive Diphasic Gas-Particle Flows
  
  • Nussbaum Julien
  • Helluy Philippe
  • Hérard Jean-Marc
  • Carrière Alain
  , 2007. (10.2514/6.2007-4161)
  DOI : 10.2514/6.2007-4161
• A review of current issues in air pollution modeling and simulation
  
  • Sportisse Bruno
  Computational Geosciences, Springer Verlag, 2007, 11 (2), pp.159-181. Air pollution modeling is now a mature field, and comprehensive numerical models (the chemistry-transport models) are used in many applications. This article aims at reviewing the main issues from the point of view of applied mathematics and computational physics (as viewed by the author). We address topics such as subgrid parameterization, numerical algorithms with a focus on aerosol simulation, data assimilation and inverse modeling, reduction of high-dimensional models and propagation of uncertainties. Even if this article is strictly related to air pollution modeling, many issues and methods can be extended to dispersion of tracers in other media (for instance, water). (10.1007/s10596-006-9036-4)
  DOI : 10.1007/s10596-006-9036-4
• Dominant aerosol processes during high-pollution episodes over Greater Tokyo
  
  • Sartelet Karine
  • Hayami Hiroshi
  • Sportisse Bruno
  Journal of Geophysical Research: Atmospheres, American Geophysical Union, 2007, 112, pp.3/4 p.. This paper studies two high-pollution episodes over Greater Tokyo: 9 and 10 December 1999, and 31 July and 1 August 2001. Results obtained with the chemistry-transport model (CTM) Polair3D are compared to measurements of inorganic PM2.5. To understand to which extent the aerosol processes modeled in Polair3D impact simulated inorganic PM2.5, Polair3D is run with different options in the aerosol module, e.g. with/without heterogeneous reactions. To quantify the impact of processes outside the aerosol module, simulations are also done with another CTM (CMAQ). In the winter episode, sulfate is mostly impacted by condensation, coagulation, long-range transport, and deposition to a lesser extent. In the summer episode, the effect of long-range transport largely dominates. The impact of condensation/evaporation is dominant for ammonium, nitrate and chloride in both episodes. However, the impact of the thermodynamic equilibrium assumption is limited. The impact of heterogeneous reactions is large for nitrate and ammonium, and taking heterogeneous reactions into account appears to be crucial in predicting the peaks of nitrate and ammonium. The impact of deposition is the same for all inorganic PM2.5. It is small compared to the impact of other processes although it is not negligible. The impact of nucleation is negligible in the summer episode, and small in the winter episode. The impact of coagulation is larger in the winter episode than in the summer episode, because the number of small particles is higher in the winter episode as a consequence of nucleation. (10.1029/2006JD007885)
  DOI : 10.1029/2006JD007885
• BEST PRACTICE GUIDELINE FOR THE CFD SIMULATION OF FLOWS IN THE URBAN ENVIRONMENT
  
  • Franke Jörg
  • Hellsten Antti
  • Schlünzen Heinke
  • Carissimo Bertrand
  , 2007. The main objective of the COST Action 732 is the improvement and quality assurance of micro-scale obstacle-accommodating meteorological models and their application to the prediction of flow and transport processes in urban or industrial environments. This report contains the full best practice guidelines for undertaking simulations that are used to evaluate microscale obstacle-accommodating meteorological models Summaries of this report have been published as the following documents : Franke, J., Hellsten, A., Schlunzen, H. A., & Carissimo, B. (2010). The Best Practise Guideline for the CFD simulation of flows in the urban environment: an outcome of COST 732. In The Fifth International Symposium on Computational Wind Engineering (CWE2010) (pp. 1-10) Franke, J., Hellsten, A., Schlunzen, K. H., & Carissimo, B. (2011). The COST 732 Best Practice Guideline for CFD simulation of flows in the urban environment: a summary. International Journal of Environment and Pollution, 44(1-4), 419-427.
• Analysis of the Black Sea surface currents retrieved from space imagery
  
  • Korotaev Gennady K.
  • Huot Etienne
  • Le Dimet François-Xavier
  • Herlin Isabelle
  • Stanichny S.V.
  • Solovyev D.M.
  , 2007.
• High resolution reconstruction of a tracer dispersion event: application to ETEX
  
  • Bocquet Marc
  Quarterly Journal of the Royal Meteorological Society, Wiley, 2007, 133 (625B), pp.1013-1026. In a previous two-part paper, new methods for reconstructing the source of an atmospheric tracer at regional scale were developed. Specifically, the 'maximum entropy on the mean' (MEM) method was extended to large (though linear) data assimilation problems. Tests using twin experiments and a limited subset of the data from the European Tracer Experiment (ETEX) were performed. Although temporal reconstruction knowing the location of the source was satisfying, a full three-dimensional reconstruction with real data was still out of reach. In this paper, using the MEM method and some of its refinements, a reconstruction using all ETEX-I measurements at a resolution of 1.125 × 1.125 × 1 h is shown to be possible. This allows for a reconstruction of the full dispersion event. The MEM retrieval of the tracer plume using what is believed to be a good prior is then compared to retrievals using other priors, including Gaussian priors. Eventually, a reconstruction using all data sequentially in time (rather than all together) is obtained. This helps define what a maximum-entropy filter applied to sequential data assimilation of a linear tracer should be able to do, with a view to an efficient emergency response in case of an accidental release of pollutant. (10.1002/qj.64)
  DOI : 10.1002/qj.64
• Partenariat recherche publique/entreprise : l'exemple du CEREA, Laboratoire Commun ENPC/EDF R&D. Chapitre 6
  
  • Sportisse Bruno
  , 2007.
• A review of parameterizations for modelling dry deposition and scavenging of radionuclides
  
  • Sportisse Bruno
  Atmospheric Environment, Elsevier, 2007, 41 (13), pp.2683-2698. This article aims at reviewing the state-of-the-science parameterizations for modelling dry deposition and scavenging of atmospheric tracers, with a focus on radionuclides. These parameterizations are key components of the numerical models that are used for environmental forecast. We present detailed models and parameterizations. Both are characterized by many uncertainties. (10.1016/j.atmosenv.2006.11.057)
  DOI : 10.1016/j.atmosenv.2006.11.057
• Source reconstruction of an accidental radionuclide release at European scale
  
  • Krysta Monika
  • Bocquet Marc
  Quarterly Journal of the Royal Meteorological Society, Wiley, 2007, 133 (623B), pp.529-544. We develop and experiment with new techniques to reconstruct the source of an accidental release of radionuclides at continental scale. The prior information on the source to be accounted for in the inversion is identified. Using methods based on information theory, purposeful cost functions consistent with this prior are constructed. They generalize classical variational least-square assimilation techniques. The adjoint of the numerical dispersion model POLAIR3D is used in the minimization of these cost functions. The method is tested on a set of twin experiments involving the main European civil nuclear sites as candidate sources. Several experiments are performed. They demonstrate how sensitive the retrievals are to the prior, the meteorological conditions, the source profile shape and the errors. A reconstruction is then attempted on the Algeciras incident, which took place in southern Spain in May 1998. A truly successful three-dimensional inversion is out of reach with the available observations. However, a temporal reconstruction of the event succeeds, and this exemplifies the newly designed cost functions. (10.1002/qj.3)
  DOI : 10.1002/qj.3
• Technical Note: A new SIze REsolved Aerosol Model (SIREAM)
  
  • Debry E.
  • Fahey K.
  • Sartelet K.
  • Sportisse B.
  • Tombette M.
  Atmospheric Chemistry and Physics, European Geosciences Union, 2007, 7 (6), pp.1547. We briefly present in this short paper a new SIze REsolved Aerosol Model (SIREAM) which simulates the evolution of atmospheric aerosol by solving the General Dynamic Equation (GDE). SIREAM segregates the aerosol size distribution into sections and solves the GDE by splitting coagulation and condensation/evaporation-nucleation. A quasi-stationary sectional approach is used to describe the size distribution change due to condensation/evaporation, and a hybrid equilibrium/dynamical mass-transfer method has been developed to lower the computational burden. SIREAM uses the same physical parameterizations as those used in the Modal Aerosol Model, MAM Sartelet et al. (2006). It is hosted in the modeling system Polyphemus Mallet et al., 2007, but can be linked to any other three-dimensional Chemistry-Transport Model.
• Inverse modelling-based reconstruction of the Chernobyl source term available for long-range transport
  
  • Davoine X.
  • Bocquet Marc
  Atmospheric Chemistry and Physics, European Geosciences Union, 2007, 7 (6), pp.1564. The reconstruction of the Chernobyl accident source term has been previously carried out using core inventories, but also back and forth confrontations between model simulations and activity concentration or deposited activity measurements. The approach presented in this paper is based on inverse modelling techniques. It relies both on the activity concentration measurements and on the adjoint of a chemistry-transport model. The location of the release is assumed to be known, and one is looking for a source term available for long-range transport that depends both on time and altitude. The method relies on the maximum entropy on the mean principle and exploits source positivity. The inversion results are mainly sensitive to two tuning parameters, a mass scale and the scale of the prior errors in the inversion. To overcome this hardship, we resort to the statistical L-curve method to estimate balanced values for these two parameters. Once this is done, many of the retrieved features of the source are robust within a reasonable range of parameter values. Our results favour the acknowledged three-step scenario, with a strong initial release (26 to 27 April), followed by a weak emission period of four days (28 April–1 May) and again a release, longer but less intense than the initial one (2 May–6 May). The retrieved quantities of iodine-131, caesium-134 and caesium-137 that have been released are in good agreement with the latest reported estimations. Yet, a stronger apportionment of the total released activity is ascribed to the first period and less to the third one. Finer chronological details are obtained, such as a sequence of eruptive episodes in the first two days, likely related to the modulation of the boundary layer diurnal cycle. In addition, the first two-day release surges are found to have effectively reached an altitude up to the top of the domain (5000 m).
• Use of proper orthogonal decomposition for the reduction of atmospheric chemical kinetics
  
  • Sportisse Bruno
  • Djouad Rafik
  Journal of Geophysical Research, American Geophysical Union, 2007, 112 (D06303). We investigate in this article a method based on proper orthogonal decompositions (POD) in order to reduce atmospheric chemical mechanisms. In a preliminary test, we apply this algorithm to the reduction of the CBM IV mechanism in a box model. The reduced basis computed with POD gives accurate results in its domain of validity while the CPU time needed for integration has been drastically lowered. The number of degrees of freedom of the local reduced model is 2 or 3. Moreover, we investigate some numerical strategies and a sensitivity analysis related to the choice of the reduced basis. This reducing technique is applied to three different scenarios for initial conditions: rural, urban, and polluted. Our tests indicate the deep relation with the slow-fast behavior of chemical kinetics. (10.1029/2006JD007808)
  DOI : 10.1029/2006JD007808
• Modélisation inverse pour la qualité de l'air : éléments de méthodologie et exemples
  
  • Bocquet Marc
  • Sportisse Bruno
  Pollution Atmosphérique : climat, santé, société, APPA, 2007 (196), pp.395-404. L'objet de cet article est de donner quelques éléments méthodologiques pour la modélisation inverse des émissions en qualité de l'air : comment caractériser des émissions sur la base de données mesurées et de sorties de modèles numériques ? Trois exemples issus de travaux récents menés au sein du CEREA, Laboratoire commun ENPC/EDF R&D, permettent d'illustrer ces thématiques : la modélisation inverse de radionucléides à petite échelle, la modélisation de précurseurs de l'ozone (NOx) à l'échelle régionale (région de Lille) et l'identification d'une source accidentelle à l'échelle continentale (expérience ETEX). Il ne s'agit donc pas d'une revue exhaustive sur le sujet.
• Polyphemus : une plate-forme multimodèles pour la pollution atmosphérique et l'évaluation des risques
  
  • Mallet Vivien
  • Quélo Denis
  • Sportisse B.
  • Korsakissok Irène
  Pollution Atmosphérique : climat, santé, société, APPA, 2007 (196), pp.423-431. Cet article présente le système de modélisation de la qualité de l'air Polyphemus, ses principales fonctionnalités et quelques applications. Polyphemus est dédié à la modélisation de la dispersion atmosphérique de traceurs passifs ou d'espèces réactives aux échelles locale, régionale et continentale. Polyphemus est développé au CEREA, laboratoire commun entre EDF R&D et lʼÉcole des Ponts et au sein dʼun projet commun avec lʼInstitut national de recherche en informatique et automatique (INRIA), avec le soutien de lʼIRSN et de lʼINERIS. Polyphemus est un système dʼun type nouveau qui se distingue de lʼapproche classique du " modèle tout en un " par sa construction modulaire, notamment fondée sur des bibliothèques et des pilotes manipulant les modèles de dispersion. Accueillant plusieurs modèles, Polyphemus est une plate-forme et non un modèle. Une de ses fonctionnalités notables est sa capacité à effectuer des simulations multimodèles, ce qui permet d'évaluer des incertitudes. Plusieurs méthodes dʼassimilation de données font aussi partie du système afin de pouvoir intégrer des données fournies par des réseaux de mesure.