Publications

2017

• CHIMERE-2017 : from urban to hemispheric chemistry-transport modeling
  
  • Mailler Sylvain
  • Menut Laurent
  • Khvorostyanov Dmitry
  • Valari Myrto
  • Couvidat Florian
  • Siour Guillaume
  • Turquety Solène
  • Briant Régis
  • Tuccella Paolo
  • Bessagnet Bertrand
  • Colette Augustin
  • Letinois Laurent
  • Markakis Konstantinos
  • Meleux Frédérik
  Geoscientific Model Development, European Geosciences Union, 2017, 10, pp.2397-2423. CHIMERE is a chemistry-transport model designed for regional atmospheric composition. It can be used at a variety of scales from local to continental domains. However, due to the model design and its historical use as a regional model, major limitations had remained, hampering its use at hemispheric scale, due to the coordinate system used for transport as well as to missing processes that are important in regions outside Europe. Most of these limitations have been removed in the CHIMERE-2017 version, allowing its use in any region of the world and at any scale, from the scale of a single urban area up to hemispheric scale, with or without polar regions included. Other important improvements have been made in the treatment of the physical processes affecting aerosols and the emissions of mineral dust. From a computational point of view, the parallelization strategy of the model has also been updated in order to improve model numerical performance and reduce the code complexity. The present article describes all these changes. Statistical scores for a model simulation over continental Europe are presented, and a simulation of the circumpolar transport of volcanic ash plume from the Puyehue volcanic eruption in June 2011 in Chile provides a test case for the new model version at hemispheric scale. (10.5194/gmd-10-2397-2017)
  DOI : 10.5194/gmd-10-2397-2017
• Online learning with the Continuous Ranked Probability Score for ensemble forecasting
  
  • Thorey J.
  • Mallet V.
  • Baudin P.
  Quarterly Journal of the Royal Meteorological Society, Wiley, 2017, 143 (702), pp.521-529. Ensemble forecasting resorts to multiple individual forecasts to produce a discrete probability distribution which accurately represents the uncertainties. Before every forecast, a weighted empirical distribution function is derived from the ensemble, so as to minimize the Continuous Ranked Probability Score (CRPS). We apply online learning techniques, which have previously been used for deterministic forecasting, and we adapt them for the minimization of the CRPS. The proposed method theoretically guarantees that the aggregated forecast competes, in terms of CRPS, against the best weighted empirical distribution function with weights constant in time. This is illustrated on synthetic data. Besides, our study improves the knowledge of the CRPS expectation for model mixtures. We generalize results on the bias of the CRPS computed with ensemble forecasts, and propose a new scheme to achieve fair CRPS minimization , without any assumption on the distributions. (10.1002/qj.2940)
  DOI : 10.1002/qj.2940
• Who is the Expert? Integrated Urban Modeling and the Reconfiguration of Expertise
  
  • Commenges Hadrien
  • Tomasoni Lorenza
  • Seigneur Christian
  • Bonin Olivier
  • Leurent Fabien
  • Bonhomme Céline
  • Deroubaix José-Frédéric
  Journal of Urban Technology, Taylor & Francis (Routledge): SSH Titles, 2017, 24 (2), pp.89-108. Much has been spoken and written about the rationalization and optimization of services and amenities in urban territories. In this context, there is increasing use of numerical modeling techniques addressing the design, selection and/or calibration of policy instruments. The question of the relations between appraisal tools and policymaking has been widely studied. However, few studies have specifically focused on the role of modeling in policymaking processes. Drawing on two case studies, this paper suggests a change in the nature of multi-expertise: neither conflicting nor cross-sectoral, we observed in both cases an interwoven configuration with a network of experts making use of integrated models. We call this configuration distributed expertise, arguing that it is a novel configuration and that its emergence is closely linked to the development of integrated modeling techniques. Other authors have discussed the idea that the growing need for new appraisal tools is linked with the proliferation of wicked policy problems. From our case studies we would conclude that the emergence of integrated modeling is not a response to complex problems but to complex systems of actors who need to reach a consensus on actions. (10.1080/10630732.2017.1284990)
  DOI : 10.1080/10630732.2017.1284990
• Statistical atmospheric inversion of local gas emissions by coupling the tracer release technique and local-scale transport modelling: a test case with controlled methane emissions
  
  • Ars Sébastien
  • Broquet Grégoire
  • Yver Kwok Camille
  • Roustan Yelva
  • Wu Lin
  • Arzoumanian Emmanuel
  • Bousquet Philippe
  Atmospheric Measurement Techniques, European Geosciences Union, 2017, 10 (12), pp.5017 - 5037. This study presents a new concept for estimating the pollutant emission rates of a site and its main facilities using a series of atmospheric measurements across the pollutant plumes. This concept combines the tracer release method, local-scale atmospheric transport modelling and a statistical atmospheric inversion approach. The conversion between the controlled emission and the measured atmospheric concentrations of the released tracer across the plume places valuable constraints on the atmospheric transport. This is used to optimise the configuration of the transport model parameters and the model uncertainty statistics in the inversion system. The emission rates of all sources are then inverted to optimise the match between the concentrations simulated with the transport model and the pollutants' measured atmospheric concentrations, accounting for the transport model uncertainty. In principle, by using atmospheric transport modelling, this concept does not strongly rely on the good colocation between the tracer and pollutant sources and can be used to monitor multiple sources within a single site, unlike the classical tracer release technique. The statistical inversion framework and the use of the tracer data for the configuration of the transport and inversion modelling systems should ensure that the transport modelling errors are correctly handled in the source estimation. The potential of this new concept is evaluated with a relatively simple practical implementation based on a Gaussian plume model and a series of inversions of controlled methane point sources using acetylene as a tracer gas. The experimental conditions are chosen so that they are suitable for the use of a Gaussian plume model to simulate the atmospheric transport. In these experiments, different configurations of methane and acetylene point source locations are tested to assess the efficiency of the method in comparison to the classic tracer release technique in coping with the distances between the different methane and acetylene sources. The results from these controlled experiments demonstrate that, when the targeted and tracer gases are not well collocated, this new approach provides a better estimate of the emission rates than the tracer release technique. As an example, the relative error between the estimated and actual emission rates is reduced from 32 % with the tracer release technique to 16 % with the combined approach in the case of a tracer located 60 m upwind of a single methane source. Further studies and more complex implementations with more advanced transport models and more advanced optimisations of their configuration will be required to generalise the applicability of the approach and strengthen its robustness. (10.5194/amt-10-5017-2017)
  DOI : 10.5194/amt-10-5017-2017
• Modelling organic aerosol concentrations and properties during ChArMEx summer campaigns of 2012 and 2013 in the western Mediterranean region
  
  • Chrit Mounir
  • Sartelet Karine
  • Sciare Jean
  • Pey Jorge
  • Marchand Nicolas
  • Couvidat Florian
  • Sellegri Karine
  • Beekmann Matthias
  Atmospheric Chemistry and Physics, European Geosciences Union, 2017, 17 (20), pp.12509-12531. In the framework of the Chemistry-Aerosol Mediterranean Experiment, a measurement site was set up at a remote site (Ersa) on Corsica Island in the northwestern Mediterranean Sea. Measurement campaigns performed during the summers of 2012 and 2013 showed high organic aerosol concentrations, mostly from biogenic origin. This work aims to represent the organic aerosol concentrations and properties (oxidation state and hydrophilicity) using the air-quality model Polyphemus with a surrogate approach for secondary organic aerosol (SOA) formation. Biogenic precursors are isoprene, monoterpenes and sesquiterpenes. In this work, the following model oxidation products of monoterpenes are added: (i) a carboxylic acid (MBTCA) to represent multi-generation oxidation products in the low-NOx regime, (ii) organic nitrate chemistry and (iii) extremely low-volatility organic compounds (ELVOCs) formed by ozonolysis. The model shows good agreement of measurements of organic concentrations for both 2012 and 2013 summer campaigns. The modelled oxidation property and hydrophilic organic carbon properties of the organic aerosols also agree reasonably well with the measurements. The influence of the different chemical processes added to the model on the oxidation level of organics is studied. Measured and simulated water-soluble organic carbon (WSOC) concentrations show that even at a remote site next to the sea, about 64 % of the organic carbon is soluble. The concentrations of WSOC vary with the origins of the air masses and the composition of organic aerosols. The marine organic emissions only contribute to a few percent of the organic mass in PM$_1$, with maxima above the sea. (10.5194/acp-17-12509-2017)
  DOI : 10.5194/acp-17-12509-2017