5-year analysis of submicron aerosol chemical composition and organic aerosol source apportionment at a suburban site in North-Western Europe

International audienceIn Europe, more than 307 000 premature deaths havebeen attributed to fine particle exposure (EEA, 2021). Inparticular, northern France is affected by relatively highparticle matter (PM) concentrations, frequentlyexceeding the new annual PM2.5 concentration of 5μg m-3 recommended by the WHO (EEA, 2021).Therefore, the study of aerosol particle sources isessential to improve air quality and to better developeffective mitigation policies.In this context, an Aerosol Chemical SpeciationMonitor (ACSM) and an aethalometer (AE33) have beenrunning quasi continuously since 2016 at a suburbansite in Lille, known as the ATOLL (AtmosphericObservations in liLLe) platform, located on theUniversity of Lille campus. The objective is to provide acomprehensive dataset of the chemical composition ofsubmicron aerosol particles (PM1), and to investigateOrganic Aerosol (OA) sources in the region throughsource apportionment analysis using Positive MatrixFactorization (PMF). Wind and back-trajectory analysisare also used to help identifying the geographical originsof advected aerosol particles, especially since Lille is atthe crossroads of transnational pollution transport fromBelgium, Germany, the Netherlands and the UK.Here, we present the first long-term analysis ofnon-refractory PM1 (NR-PM1) from October 2016 untilDecember 2020. The average NR-PM1 concentrationwas 9.7 μg m-3, which was dominated by OA (45.4 %)followed by nitrate (31.4 %), ammonium (13.4 %) andsulfate (9.4 %). To study OA origins, we used the rollingPMF algorithm, analyzing one-month windows shiftedby one-week step. Such approach combined with welldefinedconstraints has the advantage of capturing thepotential temporal changes in the source profilesthroughout the seasons and years.The OA PMF analysis yielded two primary OAfactors: a traffic related hydrocarbon-like OA (HOA) andbiomass burning OA (BBOA), and two oxygenated OA(OOA) factors. HOA showed a fairly constantcontribution to OA throughout the seasons (with anaverage contribution of 12 %), while BBOA varied from8 % to 18.5 %, with a peak in winter due to increasedemissions from residential wood combustion. The OOAfactors were distinguished between their less and moreoxidized fractions (LO-OOA and MO-OOA, respectively).They contributed substantially to the total OA mass,with an average of 74 % (32 % and 42 % for LO-OOA andMO-OOA, respectively), indicating a strong participationof aged/secondary processes to local aerosol levels. Aregional signature of those OOA factors is confirmed viawind and trajectory analysis, identifying the impact ofpolluted continental air masses from central Europe.During winter, the correlation between BBOA and LOOOAsuggests the influence of aged biomass burning onthe latter, identifying at least half of OA to be associatedto wood combustion during wintertime. This wasconfirmed by complementary PMF analyses includinginorganic and black carbon components.Overall, this study provides a thorough analysis ofsubmicron aerosol sources at the recently establishedATOLL platform, depicting complex interactionsbetween regional traffic, wood burning, and agriculturalactivities in the highly urbanized North-WesternEuropean region.This work was supported by the French Ministry ofEnvironment, through the CARA program. It is also partof the Labex CaPPA project (ANR-11-LABX-0005-01), andthe CLIMIBIO project, both also funded by the RegionalCouncil “Hauts-de-France” and the European RegionalDevelopment Fund (ERDF)