Measurement report: Long-term real-time characterisation of the
submicronic aerosol and its atmospheric dynamic in a Mediterranean
coastal city: Tracking the polluted events at the Marseille-Longchamp
supersite
Authors: Chazeau Benjamin , Temime-Roussel Brice , Gille Grégory , Mesbah Boualem , D'Anna Barbara , Wortham Henri , Marchand Nicolas 
Published: October 2020

Abstract. A supersite was recently implemented in Marseille to conduct intensive and advanced measurement studies for ambient aerosols. A Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) was deployed to investigate the chemical composition of submicronic aerosol over a 14-month period (1 February 2017–13 April 2018). Parallel measurements were performed with an Aethalometer, an ultrafine particle monitor and a suite of instruments to monitor regulated pollutants (PM2.5, PM10, NOx, O3 and SO2). The averaged PM1 chemical composition over the period was dominated by organics (49.7 %) and black carbon (17.1 %) while sulfate accounted for 14.6 %, nitrate for 10.2 %, ammonium for 7.9 % and chloride for 0.5 % only. Wintertime was found to be the season contributing the most to the annual PM1 mass concentration (30 %), followed by autumn (26 %), summer (24 %) and spring (20 %). During this season, OA and BC concentrations were found to contribute to 32 % and 31 % of their annual concentrations, respectively, as a combined result of heavy urban traffic, high emissions from residential heating, open combustion of green wastes and low planetary boundary layer (PBL) height. In summer, sulfate contribution to PM1 increased with an average and a maximum contribution to the PM1 of 24 % and 66 %. This is partly due to local photochemical production from its precursor SO2, locally emitted by shipping and industrial activities and advected to the city under sea breeze conditions. Results from backtrajectory cluster analysis suggest that, besides local anthropogenic activities, Mediterranean long-range transport contributes the most to the enrichment of the sulfate fraction. Another important feature of the summer season is that half of the most intense SO2 peaks happen at that time of the year and are associated to higher UFPs number. The fifteen days exceeding the target daily PM2.5 concentration value recommended by the World Health Organization (WHO) occurred during the cold period (late autumn-early spring). These episodes contribute to an increase of 6.5 % of the annual PM1 concentration. Local and long-range pollution episodes could be distinguished, accounting for 40 and 60 % of the exceedance days, respectively. Enhanced OA and BC concentrations, mostly originating from domestic wood burning under nocturnal land breeze conditions were observed during local pollution episodes, while high level of oxygenated OA and inorganic nitrate were associated to medium/long-range transported particles. In conclusion this supersite showed a high potential for the study of seasonality and pollution episodes phenomenology in Marseille over multiple geographic scales. The present paper highlights the significant contribution of regional transport of pollutants to the local air pollution that must be considered by local authorities in deploying effective PM abatement strategies.