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Optimization of Monitoring Networks for Air Quality

Project R2DS 2007-21

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  • Official Link : click here.
  • Syllabus
  • Objective
    • Air quality, due to its impact on nature and human society, has to be assessed, partly based on the observations from monitoring networks, and partly from the physical or statistical knowledge. The underlying atmospheric random field is heterogeneous, consequently the way how the field is observed does matter. Determining the optimal network positioning for the air quality evaluation, is of both theoretical and practical importance. We will investigate several network design problems, which differ in the design criterion, the underlying random field, and the algorithm for the selection of monitoring sites. The design methodology will be proposed correspondingly.
  • Approaches
    • Existing approaches are, for instance, the optimum experimental design and the maximum entropy principle. For the former, elaborate theory has been developed mainly based on the linear regression, which relates the network configurations to certain criteria, e.g. A, D, E, and G design. The objective of these experiments are mainly for the hypothesis testing and the parameter estimation. For the latter, the design is usually coupled with Bayesian inference of model parameters. Intuition criteria are proposed, e.g. maximum information gain from the network to be constructed.
    • Our approach is, first of all, aiming at practical interests, such as the evaluation of the efficiency of existing networks and the assimilation of new type of observations say from LIDAR stations. Since the design criteria are often related to the estimation of the underlying random field, we will firstly develop and validate the estimation methods, which should be appropriate in the network design context. More precisely, the geostatistical methods, also called kriging methods, are examined taking into account the properties of the concerned random field, e.g. the diurnal behavior of ozone. Then, the criteria are optimized using combinatorial optimization methods such as the simulated annealing algorithm. Finally, the design results are analyzed for practical use.
  • CEREA : Marc Bocquet (PI), Lin Wu (postdoc), Rachid Abida (Ph.D student), and Matthieu Chevallier (Master student)
Potential Partners
  • INERIS : Laurence Rouïl
  • AIRPARIF : Philippe Lameloise
  • Efficiency evaluation of BDQA network by solving a network reduction problem.
    • In this study, the efficiency of the BDQA (Base de Données sur la Qualité de l'Air, maintained by AIRPARIF) network for ozone estimation is assessed by investigating a network reduction problem. We examine how well a subset of the BDQA network can represent the full network. Several interpolation methods, namely ordinary kriging, simple kriging, kriging about means, and consistent kriging about means, are compared for a reliable ozone estimation. It is found that the statistical information about the means improves significantly the kriging results. Exponential models are employed for the spatial correlations, and it is necessary to consider the correlation model to be hourly-varying and daily stationary. The network reduction problem is solved using the simulated annealing algorithm. Significant improvements can be obtained through optimization. The potential redundant stations can thus be removed to save maintenance costs. Alternatively, the equipments of those redundant stations might be reallocated for a more efficient network.
  • Optimal redistribution of the background ozone monitoring stations
    • In this network displacement problem, a set of design objectives are assessed, e.g. geometrical criteria of space-filling type, minimization of kriging error (according to A, D or E-optimality conditions), and performance of the reconstruction of ozone fields (generated by simulations of a chemistry-transport model or by data assimilation experiments). By displacing background stations to regular grid points over France, significant improvements against the original background BDQA network have been found under all the proposed criteria. The impact of the different criteria on displacement is also investigated.
  • L. Wu and M. Bocquet, Optimal redistribution of the background ozone monitoring stations over France , Atmospheric Environment, in press, 2010
  • L. Wu, M. Bocquet, and M. Chevallier, Optimal reduction of the ozone monitoring network over France , Atmospheric Environment, 44:3071-3083, 2010,
  • L. Wu, M. Bocquet, Optimal Reduction of the BDQA Network for Ozone Assessments Over France , CEREA report, 2009
  • M. Chevallier, Conception optimale de réseaux d'observation pour la qualité de l'air , CEREA report 2008-10
  • Teaching : Marc Bocquet is in charge of one course at graduate level (ENSTA ParisTech + École des Ponts ParisTech). The course is on data assimilation algorithms, of which one session (3h30) is for the construction of monitoring network. This is, to our knowledge, the only lesson available of this kind.
  • Training : Matthieu Chevallier (4th year student at École Polytechnique) has finished one short stage from March to June in 2008. Matthieu worked in CEREA for one and a half days per week (PIL - Projet d'Ingénieur en Laboratoire, training at École des Ponts).
  • L. Wu, Network Design for Ozone Monitoring over France: Reduction of Redundant Stations and Displacement of Background Stations , oral presentation at conference TIES 2010
  • L. Wu, Network Design for Ozone Monitoring over France , oral presentation at summer school CIMPA 2010
  • L. Wu, Optimal Reduction of the BDQA Network for Ozone Assessments Over France , poster presentation at EGU 2009
  • M. Bocquet, Network Design for Air Quality , oral presentation at ITM 2009
  • L. Wu, Air Quality Forecast and Applications , UCECF seminar, University Paris VI, November 22, 2008

Last Update: 23 August 2010