Two years of near real-time chemical composition of submicron aerosols in the region of Paris using an Aerosol Chemical Speciation Monitor (ACSm) and a multi-wavelength Aethalometer

Abstract

Abstract. Aerosol Mass Spectrometer (AMS) measurements have been successfully used towards a better understanding of non-refractory submicron (PM1) aerosol chemical properties based on short-term campaign. The recently developed Aerosol Chemical Speciation Monitor (ACSM) has been designed to deliver quite similar artefact-free chemical information but for low-cost, and to perform robust monitoring over long-term period. When deployed in parallel with real-time Black Carbon (BC) measurements, the combined dataset allows for a quasi-comprehensive description of the whole PM1 fraction in near real-time. Here we present a 2 year long ACSM and BC datasets, between mid-2011 and mid-2013, obtained at the French atmospheric SIRTA supersite being representative of background PM levels of the region of Paris. This large dataset shows intense and time limited (few hours) pollution events observed during wintertime in the region of Paris pointing to local carbonaceous emissions (mainly combustion sources). A non-parametric wind regression analysis was performed on this 2 year dataset for the major PM1 constituents (organic matter, nitrate, sulphate and source apportioned BC) and ammonia in order to better refine their geographical origins and assess local/regional/advected contributions which information are mandatory for efficient mitigation strategies. While ammonium sulphate typically shows a clear advected pattern, ammonium nitrate partially displays a similar feature, but less expected, it also exhibits a significant contribution of regional and local emissions. Contribution of regional background OA is significant in spring and summer while a more pronounced local origin is evidenced during wintertime which pattern is also observed for BC originating from domestic wood burning. Using time-resolved ACSM and BC information, seasonally differentiated weekly diurnal profiles of these constituents were investigated and helped to identify the main parameters controlling their temporal variations (sources, meteorological parameters). Finally, a careful investigation of all the major pollution episodes observed over the region of Paris between 2011 and 2013 was performed and classified in terms of chemical composition and BC-to-sulphate ratio used here as a proxy of the local/regional vs. advected contribution of PM. In conclusion, these first 2 year quality-controlled measurements of ACSM clearly demonstrate their great potential to monitor on a long term basis aerosol sources and their geographical origin and provide strategic information in near real-time during pollution episodes. They also support the capacity of the ACSM to be proposed as a robust and credible alternative to filter-based sampling techniques for long term monitoring strategies.