Volatile organic compound sources and impacts in an urban Mediterranean area (Marseille, France)

Abstract. Long-term measurements of volatile organic compound (VOC) concentrations are crucial to improve our knowledge about their role in atmospheric chemistry, especially in regions with high photochemistry, such as the Mediterranean Basin. A field measurement campaign of 18 months has been conducted in Marseille from March 2019 to August 2020 with online measurements of C2 to C16 non-methane hydrocarbons (NMHCs) using two thermal desorber–gas chromatography–flame ionization detector (TD-GC-FID) instruments. The positive matrix factorization model has been applied to this dataset for each season. Six yearlong factors were identified (traffic exhaust, fuel evaporation, industrial sources, shipping, regional and local urban backgrounds, and IVOCs), and two seasonal factors were identified (biogenic sources in summer and residential heating during cold periods). Traffic (exhaust and evaporation) is the largest contributor to measured NMHC concentrations, with a relative contribution of about 40 %, with the exception of spring 2020, where the relative contribution was only 25 %. The potential contribution of each factor to secondary pollutant formation has been evaluated. Results reveal that the shipping source is potentially one of the most important contributors to secondary organic aerosol formation potential, despite the low contribution of this factor to NMHC concentrations. The impact of the lockdown due to Covid-19 is clearly visible across all sources, especially the traffic source. The contribution of this source decreased by half during spring 2020 in comparison with other seasons. A comparison of these results with emission inventories may be useful to evaluate their accuracy for a better understanding of the atmospheric pollution occurring in Marseille.