Polyphemus : une plate-forme multimodèles pour la pollution atmosphérique et l'évaluation des risques

National audienceCet 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

A comprehensive study of ozone sensitivity with respect to emissions over Europe with a chemistry-transport model

International audienceA detailed sensitivity analysis of ozone concentrations with respect to anthropogenic and biogenic emissions is performed at European scale in summer 2001 through the use of the chemistry-transport model Polair3D. We estimate the time evolution of the sensitivities and the extent of the sensitive regions. We discriminate the chemical species to which photochemistry is the most sensitive. This work is intended as a preliminary study for inverse modeling of emissions. Local sensitivities are computed using a tangent linear model and an adjoint model of the underlying chemistry-transport model. Global sensitivities are approximated by means of Monte Carlo simulations. It is shown that NO emissions have a prominent impact and that VOC emissions also play an important role. Major emission sources are associated with the highest sensitivities, although a non-negligible sensitivity of the concentrations at observation stations can cover the whole domain. A typical relative sensitivity of ozone concentrations to NO emissions is about 6 μg * m−3, which is low as to compared to the error and the uncertainty in output concentrations

Inverse modeling of NOx emissions at regional scale over northern France: Preliminary investigation of the second-order sensitivity

International audienceThe purpose of this article is to perform the inverse modeling of emissions at regional scale for photochemical applications. The case study is the region of Lille in northern France for simulations in May 1998. The chemistry-transport model, Polair3D, has been validated with 1 year of model-to-observation comparisons over Lille. Polair3D has an adjoint mode, which enables inverse modeling with a variational approach. A sensitivity analysis has been performed so as to select the emission parameters to be modified in order to improve ozone forecasts. It has been shown that inverse modeling of the time distribution of nitrogen oxide emissions leads to satisfactory improvements even after the learning period. A key issue is the robustness of the inverted emissions with respect to uncertain parameters. A brute force second-order sensitivity analysis of the optimized emissions has been performed with respect to other parameters and has proven that the optimized time distribution of NOx emissions is robust

Investigation of some numerical issues in a chemistry-transport model: Gas-phase simulations

International audienceMany 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

Technical Note: The air quality modeling system Polyphemus

International audiencePolyphemus 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

Extracellular laminin regulates hematopoietic potential of pluripotent stem cells through integrin β1-ILK-β-catenin-JUN axis

血液細胞へ効率よく変化させる弱い接着を明らかに --血液細胞の産生効率を向上--. 京都大学プレスリリース. 2021-03-31.Stuck stem cells are no good at making blood. 京都大学プレスリリース. 2021-03-31.Recombinant matrices have enabled feeder cell-free maintenance cultures of human pluripotent stem cells (hPSCs), with laminin 511-E8 fragment (LM511-E8) being widely used. However, we herein report that hPSCs maintained on LM511-E8 resist differentiating to multipotent hematopoietic progenitor cells (HPCs), unlike hPSCs maintained on LM421-E8 or LM121-E8. The latter two LM-E8s bound weakly to hPSCs compared with LM511-E8 and activated the canonical Wnt/β-catenin signaling pathway. Moreover, the extracellular LM-E8-dependent preferential hematopoiesis was associated with a higher expression of integrin β1 (ITGB1) and downstream integrin-linked protein kinase (ILK), β-catenin and phosphorylated JUN. Accordingly, the lower coating concentration of LM511-E8 or addition of a Wnt/β-catenin signaling activator, CHIR99021, facilitated higher HPC yield. In contrast, the inhibition of ILK, Wnt or JNK by inhibitors or mRNA knockdown suppressed the HPC yield. These findings suggest that extracellular laminin scaffolds modulate the hematopoietic differentiation potential of hPSCs by activating the ITGB1-ILK-β-catenin-JUN axis at the undifferentiated stage. Finally, the combination of low-concentrated LM511-E8 and a revised hPSC-sac method, which adds bFGF, SB431542 and heparin to the conventional method, enabled a higher yield of HPCs and higher rate for definitive hematopoiesis, suggesting a useful protocol for obtaining differentiated hematopoietic cells from hPSCs in general

Retinoid-Induced Expression and Activity of an Immediate Early Tumor Suppressor Gene in Vascular Smooth Muscle Cells

Retinoids are used clinically to treat a number of hyper-proliferative disorders and have been shown in experimental animals to attenuate vascular occlusive diseases, presumably through nuclear receptors bound to retinoic acid response elements (RARE) located in target genes. Here, we show that natural or synthetic retinoids rapidly induce mRNA and protein expression of a specific isoform of A-Kinase Anchoring Protein 12 (AKAP12β) in cultured smooth muscle cells (SMC) as well as the intact vessel wall. Expression kinetics and actinomycin D studies indicate Akap12β is a retinoid-induced, immediate-early gene. Akap12β promoter analyses reveal a conserved RARE mildly induced with atRA in a region that exhibits hyper-acetylation. Immunofluorescence microscopy and protein kinase A (PKA) regulatory subunit overlay assays in SMC suggest a physical association between AKAP12β and PKA following retinoid treatment. Consistent with its designation as a tumor suppressor, inducible expression of AKAP12β attenuates SMC growth in vitro. Further, immunohistochemistry studies establish marked decreases in AKAP12 expression in experimentally-injured vessels of mice as well as atheromatous lesions in humans. Collectively, these results demonstrate a novel role for retinoids in the induction of an AKAP tumor suppressor that blocks vascular SMC growth thus providing new molecular insight into how retiniods may exert their anti-proliferative effects in the injured vessel wall

Observational network design, adaptive observations and targeting strategies in atmospheric data assimilation : sketch of a methodological review

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Simulation numérique et assimilation de données variationnelle pour la dispersion atmosphérique de polluants

This work has led to the development of a three-dimensional chemistry-transport model Polair3D which simulates photochemistry. Model-to-data comparison of ozone and nitrogen oxides measurements over Lille in 1998 has proven its reliability at regional scale. 4 D-var data assimilation has been implemented. It relies on the adjoint model of Polair3D obtained through automatic differentiation. An application of inverse modelling of emissions over Lille with real measurements has been performed. It has proven that the inversion of temporal parameters of nitrogen oxides emissions leads to a significant improvement of forecasts. The so-called second-order sensitivity allows to study the sensitivity of the inversion with respect to the data assimilation system itself by computing its conditioning. This is illustrated by two test cases: short-range dispersion of radionuclides and gas-phase atmospheric chemistry characterized by a wide range of timescales.Ce travail a permis de développer un modèle de chimie-transport tridimensionnel Polair3D pour simuler la pollution photochimique. Des comparaisons aux mesures d'ozone et d'oxydes d'azote sur la région de Lille pour l'année 1998 l'ont validé à l'échelle régionale. La méthode d'assimilation de données 4D-var a été implémentée. Elle est basée sur le modèle adjoint de Polair3D qui a été obtenu par différenciation automatique. Une application à la modélisation inverse des émissions sur Lille avec des observations réelles a montré que l'inversion de paramètres temporels d'émissions d'oxydes d'azote permet d'améliorer notablement les prévisions. La sensibilité de "second-ordre" permet d'étudier la sensibilité de l'inversion au système d'assimilation de données lui-même en calculant son conditionnement. Cette problématique est illustrée sur deux applications: la dispersion de radionucléides à petite échelle et la chimie atmosphérique, caractérisée par sa disparité d'échelles temporelles

Impact of mass consistency errors for atmospheric dispersion

International audienceAtmospheric 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)