Characterising an intense PM pollution episode in March 2015 in France from multi-site approach and near real time data: Climatology, variabilities, geographical origins and model evaluation J.-E. Petit a, * , T. Amodeo b , F. Meleux b , B. Bessagnet b , L. Menut c , D. Grenier d , Y. Pellan d , A. Ockler a , B. Rocq e , V. Gros f , J. Sciare f, g , O. Favez b, ** a Air Lorraine, 20 rue Pierre Simon de Laplace, 57070 Metz, France b INERIS, rue Jacques Taffanel, 60550 Verneuil-en-Halatte, France c Laboratoire de M et eorologie Dynamique, Palaiseau, France d Air Rh^ one-Alpes, 3 all ee des Sorbiers, 69500 Bron, France e Atmo Picardie, 22 boulevard Michel Strogoff, 80332 Longueau, France f Laboratoire des Sciences du Climat et de l’Environnement, CEA/Orme des Merisiers, 91191 Gif-sur-Yvette, France g The Cyprus Institute, Energy Environment Water Research Center, Nicosia, Cyprus highlights  A severe particulate matter pollution episode in France has been studied in four sites across the country.  Climatology analysis shows the role of atmospheric variability in the formation of such episode.  Spatial heterogeneities highlight the role of local sources and processes, as well as transboundary transport.  The performance of Chemistry-Transport Model CHIMERE depends on air mass origin. article info Article history: Received 8 November 2016 Received in revised form 5 February 2017 Accepted 6 February 2017 Available online 8 February 2017 Keywords: Aerosol Pollution France Aerosol chemical speciation monitor ACSM Aethalometer Model abstract During March 2015, a severe and large-scale particulate matter (PM) pollution episode occurred in France. Measurements in near real-time of the major chemical composition at four different urban background sites across the country (Paris, Creil, Metz and Lyon) allowed the investigation of spatio- temporal variabilities during this episode. A climatology approach showed that all sites experienced clear unusual rain shortage, a pattern that is also found on a longer timescale, highlighting the role of synoptic conditions over Wester-Europe. This episode is characterized by a strong predominance of secondary pollution, and more particularly of ammonium nitrate, which accounted for more than 50% of submicron aerosols at all sites during the most intense period of the episode. Pollution advection is illustrated by similar variabilities in Paris and Creil (distant of around 100 km), as well as trajectory analyses applied on nitrate and sulphate. Local sources, especially wood burning, are however found to contribute to local/ regional sub-episodes, notably in Metz. Finally, simulated concentrations from Chemistry-Transport model CHIMERE were compared to observed ones. Results highlighted different patterns depending on the chemical components and the measuring site, reinforcing the need of such exercises over other pollution episodes and sites. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Particulate pollution is nowadays subject to extensive studies notably due to particulate concentrations that exceed the recom- mended limits and demonstrated health effects on a short- and long-term perspective (Ramgolam et al., 2009; IARC, 2013). Also, increasing population density within urban areas tends to enhance * Corresponding author. ** Corresponding author. E-mail addresses: jean-eudes.petit@atmo-grandest.eu (J.-E. Petit), olivier.favez@ ineris.fr (O. Favez). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv http://dx.doi.org/10.1016/j.atmosenv.2017.02.012 1352-2310/© 2017 Elsevier Ltd. All rights reserved. Atmospheric Environment 155 (2017) 68e84