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

摘要

Aerosol mass spectrometer (AMS) measurements have been successfully used towards a betterunderstanding of non-refractory submicron (PM) aerosol chemicalproperties based on short-term campaigns. The recently developed AerosolChemical Speciation Monitor (ACSM) has been designed to deliver quite similarartifact-free chemical information but for low cost, and to perform robustmonitoring over long-term periods. When deployed in parallel with real-timeblack carbon (BC) measurements, the combined data set allows for aquasi-comprehensive description of the whole PM fraction in near realtime. Here we present 2-year long ACSM and BC data sets, between mid-2011 andmid-2013, obtained at the French atmospheric SIRTA supersite that isrepresentative of background PM levels of the region of Paris. This largedata set shows intense and time-limited (a few hours) pollution eventsobserved during wintertime in the region of Paris, pointing to localcarbonaceous emissions (mainly combustion sources). A non-parametric windregression analysis was performed on this 2-year data set for the majorPM constituents (organic matter, nitrate, sulfate and source apportioned BC) and ammonia in order to betterrefine their geographical origins and assess local/regional/advectedcontributions whose information is mandatory for efficient mitigation strategies. While ammoniumsulfate typically shows a clear advected pattern, ammonium nitrate partiallydisplays a similar feature, but, less expectedly, it also exhibits asignificant contribution of regional and local emissions. The contribution ofregional background organic aerosols (OA) issignificant in spring and summer, while a more pronounced local origin isevidenced during wintertime, whose pattern is also observed for BCoriginating from domestic wood burning. Using time-resolved ACSM and BCinformation, seasonally differentiated weekly diurnal profiles of theseconstituents were investigated and helped to identify the main parameterscontrolling their temporal variations (sources, meteorological parameters).Finally, a careful investigation of all the major pollution episodes observedover the region of Paris between 2011 and 2013 was performed and classifiedin terms of chemical composition and the BC-to-sulfate ratio used here as aproxy of the local/regional/advected contribution of PM. In conclusion, thesefirst 2-year quality-controlled measurements of ACSM clearly demonstratetheir great potential to monitor on a long-term basis aerosol sources andtheir geographical origin and provide strategic information in near real timeduring pollution episodes. They also support the capacity of the ACSM to beproposed as a robust and credible alternative to filter-based samplingtechniques for long-term monitoring strategies.