Multi-year source apportionment of highly-time resolved carbonaceous aerosol in the region of Paris, France
Résumé
Carbonaceous particulate matter accounts for a large fraction of fine atmospheric aerosol particles and plays a significant role on air quality and climate forcing. Although various primary sources and secondary transformation processes have already been identified and quantified worldwide, its characterization over long term time periods remains poorly documented. We report here the first source apportionment of carbonaceous aerosols for a 5+ year period from in situ on line measurements at a suburban background site (SIRTA) located in the Paris region (France). Submicron non refractory aerosols were measured using an aerosol chemical speciation monitor (ACSM) with a 30 min time resolution, while equivalent mass concentration of BC was measured by a seven wavelength aethalometer with 1 min frequency. The relative source contributions of wood burning and traffic emissions to black carbon were estimated using the ‘aethalometer model’. Positive matrix factorization, based on ME 2 engine, was applied to apportion the organic aerosol (OA) sources using the advanced Source Finder toolkit (SoFi Pro), specifically designed to robustly identify the expected factors even over multi year time scales. Results obtained with SoFi Pro were then compared to the standard SoFi outputs, corresponding to 12 successive ME 2 computations for the 2014 2017 period. Converging results nicely illustrated seasonal, weekly, and diurnal cycles of the various primary and secondary carbonaceous aerosol fractions, and offer a unique immersion into the seasonal characteristics of secondary OA (SOA) in Paris. Primary carbonaceous showed higher concentrations in winter due to enhanced wood burning emissions during the heating season. SOA dominated the total carbonaceous aerosol loading all around the year as a result of regional transport and local physicochemical formation processes. Less and more oxidized SOA fractions have been highlighted for the entire studied period. Finally, the impact of aqueous (heterogeneous) and photochemical processes on the SOA formation was also addressed.