Atmos. Chem. Phys. Discuss., 12, 33219-33263, 2012
© Author(s) 2012. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Estimation of volatile organic compound emissions for Europe using data assimilation
M. R. Koohkan1,2, M. Bocquet1,2, Y. Roustan1, Y. Kim1, and C. Seigneur1
1Université Paris-Est, CEREA, joint laboratory École des Ponts ParisTech and EDF R&D, Champs-sur-Marne, France
2INRIA, Paris Rocquencourt research centre, France

Abstract. The emission of volatile organic compounds (VOCs) over western Europe for the year 2005 are estimated via inverse modelling, by assimilation of in situ observations of concentration and compared to a standard emission inventory. The study focuses on fifteen VOC species: five aromatics, six alkanes, two alkenes, one alkyne and one biogenic diene. The inversion relies on a validated fast adjoint of the chemistry transport model used to simulate the fate and transport of these VOCs. The assimilated ground-based measurements over Europe are provided by the European Monitoring and Evaluation Programme (EMEP) network. The background emissions errors and the prior observational errors are estimated by maximum likelihood approaches. The positivity assumptions on the VOC emission fluxes is pivotal for a successful inversion and this maximum likelihood approach consistently accounts for the positivity of the fluxes. For most species, the retrieval leads to a significant reduction of the bias, which underlines the misfit between the standard inventories and the observed concentrations. The results are validated through a forecast test and a cross-validation test. It is shown that the statistically consistent non-Gaussian approach based on a reliable estimation of the errors offers the best performance. The efficiency in correcting the inventory depends on the lifetime of the VOCs. In particular, it is shown that the use of in-situ observations using a sparse monitoring network to estimate emissions of isoprene is inadequate because its short chemical lifetime significantly limits the spatial radius of influence of the monitoring data. For species with longer lifetime (a few days), successful, albeit partial, emission corrections can reach regions hundreds of kilometres away from the stations. Domainwide corrections of the emissions inventories of some VOCs are significant, with underestimations on order of a factor of two of propane, ethane, ethylene and acetylene.

Citation: Koohkan, M. R., Bocquet, M., Roustan, Y., Kim, Y., and Seigneur, C.: Estimation of volatile organic compound emissions for Europe using data assimilation, Atmos. Chem. Phys. Discuss., 12, 33219-33263, doi:10.5194/acpd-12-33219-2012, 2012.
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