The understanding of atmospheric particulate pollution represents one of the most important scientific challenges of our time, due various effects on climate and public health. These impacts are regularly highlighted during pollution episode occurring in densely urbanized areas. In Northern Europe, and more particularly in France, most intense and persistent episodes usually occur during spring, and are characterized by a large-scale pattern, covering most of the territory. Specific episodes are generally investigated from a single measurement point, describing the synergy between sources, chemical composition and meteorological conditions over a local to a regional scale. In this context, the development of aerosol mass spectrometry measurements greatly improved our knowledge of pollution (trans-)formation. Yet, this approach conceptually fails to get the bigger picture of large-scale pollution episodes, as multi-site characterization is needed. The presented work focuses on the investigation of the intense PM pollution episode that occurred in March 2015 from multi-site observations and near real time data. Aerosol Chemical Speciation Monitor (ACSM, Ng et al., 2011) and 7-wavelength aethalometer (AE33, Drinovec et al., 2015) measurements were carried out in Lyon, Metz, Creil and at SIRTA (Fig. 1)..
