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
Résumé
The understanding of atmospheric particulate pollution still represents important issues, due various effects on climate and public health. These impacts are 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. The presented work focuses on the investigation of the intense PM pollution episode that occurred in March 2015 in France from multi-site observations and near real time data. Aerosol Chemical Speciation Monitor and 7-wavelength aethalometer measurements were carried out in 4 sites across the country. A climatology approach showed that this episode is associated at all sites with clear rain shortage compared to normal values. When looking back until 2007, unusually high PM concentrations are always associated to pronounced rain shortage. If this trend become confirmed, this could be an illustration of the regional impact of climate change, and its link with air quality issues. Despite a clear dominance of secondary species, singularities from site to site are observed: While high amplitudes are observed in the Paris Basin, concentrations stayed fairly stable in Lyon and Metz, highlighting different transformation processes linked to different meteorology. Also, the increase of the PM1-2.5 fraction emphasizes the need of a better characterization in terms of chemical composition and sources. Also, a novel trajectory-based methodology allowed to distinguish advected from local/regional signal and showed that the sites are influenced by different long-range emission zones, and thus potentially different sources. This being of primarily importance to settle mitigation policies, coordinated over large geographical scales. Finally, modelled PM1 chemical composition by CHIMERE shows satisfying consistency for secondary pollutants, but exhibits high discrepancies for OM and BC, underlining the need of, among others, refined emission inventories and/or emission factors.