Publications

2011

• Estimating the effect of on road vehicle emission on future air quality in Paris
  
  • Roustan Yelva
  • Seigneur Christian
  • Pausader Marie
  , 2010, pp.....................
• Modeling pollutant dispersion from roadway traffic using a line source Gaussian formula
  
  • Briant Régis
  • Korsakissok Irène
  • Seigneur Christian
  , 2010, pp............................
• Assimilation d'images dans un modèle réduit pour l'estimation du mouvement.
  
  • Drifi Karim
  • Herlin Isabelle
  , 2011. Cet article décrit une méthode d'estimation du champ de vitesse apparent, sous-jacent à l'évolution temporelle d'une séquence d'images. Un modèle d'évolution, dit complet, est choisi pour représenter la dynamique du champ de vitesse et des images. La méthode de décomposition orthogonale propre est appliquée et fournit des bases de représentation des champs de vitesse et des images. La projection de Galerkin du modèle complet sur ces bases réduites définit alors le modèle réduit. Un algorithme d'assimilation variationnelle de données est conçu afin d'estimer les coefficients des champs de vitesse à partir des coefficients des images observées. Le mouvement est enfin restitué à partir de ces coefficients estimés. La méthode est validée sur des données synthétiques afin de quantifier les résultats.
• Linking multimedia environmental and PBPK models to assess health risks of lead associated to drinking water - A case study
  
  • Maurau S.
  • Ciffroy Philippe
  • Brochot Céline
  • Roustan Y.
  • Marang L.
  , 2011. Human exposure to chemicals through multiple pathways is classically estimated by the so-called 'multimedia models', calculating the distribution of contaminants among products of interest for humans (like drinking water, inhaled air, vegetables, meat, milk, etc). Combined to data describing human behavior (diet composition, time spent outside, etc), such multimedia models provide an estimation of the daily quantity inhaled or ingested by the population of interest. Once the exposure scenario is identified, the dose-response assessment is typically achieved by comparing exposure outputs (e.g, the daily intake) to reference doses, estimated from toxicological data. Coupling multi-media models for different exposure pathways with a generic physiologically based pharmacokinetic (PBPK) model for the human population enables to assess directly the impact of the exposure scenarios on the chemical's concentration in the target tissues.One aim of the European 2-FUN project (Full-chain and UNcertainty Approaches for Assessing Health Risks in FUture ENvironmental Scenarios) was to develop an integrated 'multimedia-PBPK' toolbox that also incorporates uncertainty and inter-individual variability analyses by Monte Carlo simulations, and different kinds of sensitivity analysis. In the present study, an integrated modeling approach was demonstrated for predicting internal tissue concentrations of chemicals by coupling a multimedia environmental model and a PBPK model. A case study was designed for a region situated on the Seine river watershed, downstream of the Paris megacity and for lead emitted from industrial zones in the region. The limited monitoring datasets of lead concentrations in bottom sediment and in raw river water, obtained at the downstream of Paris, were used to re-construct long-term daily concentrations of lead in river water. The re-construction of longterm series of lead level played a key role for the intermediate model calibration (conducted in multimedia model), and thus for improving model input to PBPK model. In order to take into account the parametric uncertainty in the model inputs, some input parameters relevant for the multimedia model were given by probability density functions (PDFs); some generic PDFs were updated with site-specific measurements by a Bayesian approach.This case study demonstrated the feasibility of a full-chain assessment combining multimedia environmental predictions and PBPK modeling, including uncertainty analysis.
• Comparison of different gas-phase mechanisms and aerosol modules for simulating ozone and particulate matter
  
  • Sartelet Karine
  • Kim Youngseob
  • Couvidat Florian
  • Seigneur Christian
  , 2010, pp.....................
• A new algorithm to solve condensation/evaporation growth and coagulation of nanoparticles
  
  • Devilliers Marion
  • Seigneur Christian
  • Sartelet Karine
  • Debry Edouard
  • Bessagnet Bertrand
  • Rouil Laurence
  , 2011. We usually define as " nanoparticles ", those particles which present at least one dimension less than 100 nm. Several studies have measured different emission sources of nanoparticles, for indoor and outdoor air. It is also known that these particles are likely to have multiple effects on human health. (Oberdorster et al.(2005)).Aware of the risks related to nanoparticles, INERIS decided in 2009 to create a research program in order to develop a model that would be able to simulate the dynamics of nanoparticles in both confined and free atmospheres. Unlike existing models, it is necessary to follow both numerical and mass concentrations of particles in order to correctly account for the time evolution of nanoparticles and their potential health effects, as the number concentration is much more relevant for nanoparticles. This study addresses condensational growth, evaporation and coagulation. A comparative review of algorithms currently used in air quality models is presented as well as new algorithms adapted to nanoparticles. We use the sectional approach in which the size distribution is discretized into sections characterized by a fixed mean geometrical diameter, particles properties are assumed to be constant over each particle size section. Two different initial particle distributions are used, one from regional pollution in hazy conditions and another one from diesel engine emission measurements. During the simulation of condensational growth, evaporation and coagulation, the size of the particles changes. In order to maintain the fixed mean geometrical diameter of each section, we have to proceed to a redistribution of the particle mass and number concentrations at each time step: particles are then transferred to the section which corresponds to their new diameter. It appears that some of the algorithms used for redistribution are better fitted for nanoparticles, among them we present a new hybrid algorithm based on number redistribution for small sections and mass redistribution for coarse sections. Futur work will consist in including several physical processes specific to nanoparticles such as nucleation and wall deposition.
• A new method to simulate coagulation of an externally mixed particle population
  
  • Dergaoui Hilel
  • Seigneur Christian
  • Sartelet Karine
  • Debry E.
  • Bessagnet Bertrand
  • Rouil Laurence
  , 2011. The usual way to follow the particle distribution in atmosphere is to assume particles to be internally mixed. This means that particles with same size have also the same composition, hence the same physical and chemical properties. This assumption has already been lifted in order to correctly account for the elemental carbon effect on aerosol climate forcing [Jacobson 2001] and also to study pollution near emission sources [Kleeman et al. 1997], where newly emitted particles may be present with aged transported particles, with the same size but different composition. The representation of an externally mixed particle population in a 3D eulerian chemical transport model has already been developed [Jacobson 2002]. A sectional approach is used for particle size, whereas the mixing state is approached by introducing several particle distributions, each one being associated with one particular source or kind of composition. In addition, some mixing thresholds between distributions allow for a more accurate representation [Bowman et al. 2010].In this communication, we present a new method to simulate coagulation and of an externally mixed particle population. Instead of introducing several distributions, the sectional approach is extended to the particle composition. That is to say the chemical composition of particles in each size section is discretized according to the percentage of one or more of its components. The entire chemical composition space can then be partitioned for each particle size. This method allows for a rigorous treatment of coagulation, which tends to mix particles among themselves. As an example, the implementation of coagulation results in the computation of coefficients to distribute mass among size and composition sections. The advantage of this approach is first, the possibility to set composition sections as wanted and second, to choose optimally between accurate mixing state representation and cpu cost. The principles of this method are discussed and the ability of this method to represent the aerosol mixing state is demonstrated with a 0D simulation. Future work will adress the condensation/evaporation growth with this computational formulation.
• Solving ill-posed Image Processing problems using Data Assimilation
  
  • Béréziat Dominique
  • Herlin Isabelle
  Numerical Algorithms, Springer Verlag, 2011, 56 (2), pp.219-252. Data Assimilation is a mathematical framework used in environmental sciences to improve forecasts performed by meteorological, oceanographic or air quality simulation models. It aims to solve an evolution equation, describing the temporal dynamics, and an observation equation, linking the state vector and observations. In this article we use this framework to study a class of ill-posed Image Processing problems, usually solved by spatial and temporal regularization techniques. An approach is proposed to convert an ill-posed Image Processing problem in terms of a data Assimilation system, solved by a 4D-Var method. This is illustrated by the estimation of optical ow from a noisy image sequence, with the dynamic model ensuring the temporal regularity of the result. The innovation of the paper concerns first, the extensive description of the tasks to be achieved for going from an image processing problem to a data assimilation description; second, the theoretical analysis of the covariance matrices involved in the algorithm; and third a specic discretisation scheme ensuring the stability of computation for the application on optical flow estimation. (10.1007/s11075-010-9383-z)
  DOI : 10.1007/s11075-010-9383-z
• Simulation numérique de la condensation / évaporation et de la coagulation des nanoparticules
  
  • Devilliers Marion
  • Seigneur C.
  • Debry Edouard
  • Sartelet Karine
  • Bessagnet Bertrand
  • Rouil Laurence
  , 2011, pp.NC. Conscient des risques liés aux nanoparticules (particules dont au moins une des dimensions est inférieure à 100 nanomètres), l'INERIS(1) a engagé en 2009 un programme de recherche en collaboration avec le CEREA(2) afin de développer un modèle capable de simuler les transformations des nanoparticules dans les ambiances intérieures (espaces confinés) comme dans l'atmosphère. En effet, les nanoparticules sont notamment susceptibles de coaguler, de grossir par condensation, et de se déposer sur les parois; ce qui modifie leur granulométrie. Une des problématiques liée à la modélisation des nanoparticules est que leur nombre est déterminant devant leur masse, tout au contraire des particules étudiées jusqu'à présent (particules fines ou grossières dont une des dimensions est supérieure à 100 nanomètre). Différents schémas numériques ont été développés pour simuler la condensation/évaporation d'une population de particules, et un noyau de coagulation issu d'algorithmes usuels a été intégré. L'inter-comparaison de ces schémas met en évidence que certains sont plus adaptés que d'autres pour les nanoparticules. Les algorithmes qui sont appropriés pour toutes les tailles de particules sont présentés. A terme, ce modèle de dynamique des nanoparticules a vocation à être intégré dans des modèles de dispersion atmosphérique (CHIMERE) et des modèles CFD (code_Saturne EdF)
• Comparison of lidar-derived PM10 with regional modeling and ground-based observations in the frame of MEGAPOLI experiment
  
  • Royer P.
  • Chazette P.
  • Sartelet K.
  • Zhang Q. J.
  • Beekmann Matthias
  • Raut Jean-Christophe
  Atmospheric Chemistry and Physics, European Geosciences Union, 2011, 11 (20), pp.10705-10726. An innovative approach using mobile lidar measurements was implemented to test the performances of chemistry-transport models in simulating mass concentrations (PM10) predicted by chemistry-transport models. A ground-based mobile lidar (GBML) was deployed around Paris onboard a van during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) summer experiment in July 2009. The measurements performed with this Rayleigh-Mie lidar are converted into PM10 profiles using optical-to-mass relationships previously established from in situ measurements performed around Paris for urban and peri-urban aerosols. The method is described here and applied to the 10 measurements days (MD). MD of 1, 15, 16 and 26 July 2009, corresponding to different levels of pollution and atmospheric conditions, are analyzed here in more details. Lidar-derived PM10 are compared with results of simulations from POLYPHEMUS and CHIMERE chemistry-transport models (CTM) and with ground-based observations from the AIRPARIF network. GBML-derived and AIRPARIF in situ measurements have been found to be in good agreement with a mean Root Mean Square Error RMSE (and a Mean Absolute Percentage Error MAPE) of 7.2 μg m−3 (26.0%) and 8.8 μg m−3 (25.2%) with relationships assuming peri-urban and urban-type particles, respectively. The comparisons between CTMs and lidar at ~200 m height have shown that CTMs tend to underestimate wet PM10 concentrations as revealed by the mean wet PM10 observed during the 10 MD of 22.4, 20.0 and 17.5 μg m−3 for lidar with peri-urban relationship, and POLYPHEMUS and CHIMERE models, respectively. This leads to a RMSE (and a MAPE) of 6.4 μg m−3 (29.6%) and 6.4 μg m−3 (27.6%) when considering POLYPHEMUS and CHIMERE CTMs, respectively. Wet integrated PM10 computed (between the ground and 1 km above the ground level) from lidar, POLYPHEMUS and CHIMERE results have been compared and have shown similar results with a RMSE (and MAPE) of 6.3 mg m−2 (30.1%) and 5.2 mg m−2 (22.3%) with POLYPHEMUS and CHIMERE when comparing with lidar-derived PM10 with periurban relationship. The values are of the same order of magnitude than other comparisons realized in previous studies. The discrepancies observed between models and measured PM10 can be explained by difficulties to accurately model the background conditions, the positions and strengths of the plume, the vertical turbulent diffusion (as well as the limited vertical model resolutions) and chemical processes as the formation of secondary aerosols. The major advantage of using vertically resolved lidar observations in addition to surface concentrations is to overcome the problem of limited spatial representativity of surface measurements. Even for the case of a well-mixed boundary layer, vertical mixing is not complete, especially in the surface layer and near source regions. Also a bad estimation of the mixing layer height would introduce errors in simulated surface concentrations, which can be detected using lidar measurements. In addition, horizontal spatial representativity is larger for altitude integrated measurements than for surface measurements, because horizontal inhomogeneities occurring near surface sources are dampened. (10.5194/acp-11-10705-2011)
  DOI : 10.5194/acp-11-10705-2011
• Assimilation of OMI NO2 retrievals into a regional chemistry-transport model for improving air quality forecasts over Europe
  
  • Wang Xiaoni
  • Mallet Vivien
  • Berroir Jean-Paul
  • Herlin Isabelle
  Atmospheric Environment, Elsevier, 2011, 45 (2), pp.485-492. This paper presents the assimilation of satellite NO2 observations into a chemistry-transport model (CTM). The NO2 columns from Ozone Monitoring Instrument (OMI) aboard NASA Aura satellite are used during November-December 2005. These satellite observations are assimilated in an air quality model from Polyphemus, in order to better forecast NO2 in Europe. The optimal-interpolation method is applied to produce analyzed columns, and these analyzed columns are mapped to model concentrations assuming that the model vertical profile is perfect. Good consistency is seen in the comparisons of model simulations, satellite data and ground observations before assimilation. The model results with and without assimilation are then compared with ground observations for evaluating the assimilation effects. It is found that the assimilation can improve the NO2 forecasts by reducing their discrepancies against ground observations, indicating a better NO2 forecast obtained with OMI observations. Such improvements are seen in a cold season rather than in a warm one probably due to the longer lifetime of NOx and the initial condition changes having more impacts in winter. This also suggests that the assimilation of the short-lived species like NO2 is a complicate problem. (10.1016/j.atmosenv.2010.09.028)
  DOI : 10.1016/j.atmosenv.2010.09.028
• Simulation of atmospheric transport of caesium-137 from the Fukushima-Daiichi nuclear power plant over the Pacific Ocean
  
  • Winiarek Victor
  • Bocquet Marc
  , 2011. This animation shows the dispersion of the caesium-137 radioactive plume from the Fukushima-Daichii power plant over Japan, the Pacific Ocean and the West coast of North America. It depicts the activity concentration of this radionuclide at ground level. The unit is Becquerel per cubic meter. It has been simulated using the 3D numerical model Polyphemus/Polair3D which accounts for several processes such as advection by the wind, turbulent diffusion, as well as dry and wet deposition. The meteorological fields that drive this transport model simulation are from the ECMWF at a resolution of 0.25°x0.25°. The source term for the emission of caesium-137 at the power plant which is used in this simulation has been estimated by inverse modelling in Winiarek et al. 2014, as a result of a collaboration between École des Ponts ParisTech and the Institute for Nuclear Radioprotection and Safety (see references below). One must be cautious in interpreting the values since this type of simulation remains impacted by high uncertainty in the source term, in the modelling of the physical process and to a lower degree by the meteorological fields.
• Optimal redistribution of the background ozone monitoring stations over France
  
  • Wu Lin
  • Bocquet Marc
  Atmospheric Environment, Elsevier, 2011, 45 (3), pp.772--783. Ozone is a harmful air pollutant at ground level, and its concentrations are routinely measured with monitoring networks. The network design problem aims at determining the optimal positioning of the monitoring stations. In this study, the background stations of the French routine pollution monitoring network (BDQA) are partially redistributed over France under a set of design objectives. These background stations report ozone variations at large spatial scale comparable with that of a chemistry-transport model (CTM). The design criterion needs to be defined on a regular grid that covers France, where in general no ozone observations are available for validation. Geostatistical ozone estimation methods are used to extrapolate concentrations to these grid nodes. The geostatistical criteria are introduced to minimize the theoretical error of those geostatistical extrapolations. A physical criterion is also introduced to measure the ability of a network to represent a physical ozone field retrieved from CTM simulations using geostatistical extrapolation methods. A third type of criteria of geometrical nature, e.g. a maximal coverage of the design domain, are based uniquely on the distance between the network stations. To complete the network design methodology, a stochastic optimization method, simulated annealing, is employed in the algorithm to select optimally the stations. Significant improvement with all the proposed criteria has been found for the optimally redistributed network against the original background BDQA network. For instance, the relative improvements in the physical criterion value range from 21% to 32% compared to randomly relocated networks. Different design criteria lead to different optimally relocated networks. The optimal networks under physical criteria are the most heterogeneously distributed. More background stations are displaced to the coast, frontiers, and large urban agglomerations, e.g. Paris and Marseilles. The ozone heterogeneous fields are not as well reconstructed from optimal networks under geostatistical or geometrical criteria as from the optimal network obtained with the physical criterion. The values of the physical criterion for the geostatistically and geometrically optimal networks show deteriorations of about 8% and 17% respectively compared to that of the physically optimal network. (10.1016/j.atmosenv.2010.08.038)
  DOI : 10.1016/j.atmosenv.2010.08.038