VOC sources and impacts at an urban Mediterranean area (Marseille – France)

Abstract. Long-term measurements of VOC concentrations are crucial to improve our knowledge about their role in atmospheric chemistry, especially in region 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 measurement of C2 to C16 NMHC using two TD-GC-FID instruments. The positive Matrix Factorization model has been applied to this dataset for each season. Six factors were identified yearlong (traffic exhaust, fuel evaporation, industrial source, shipping, regional and local urban background and IVOC) and two were identified as seasonal factors (biogenic in summer and residential heating during cold period).

The traffic (exhaust and evaporation) is the first contributor to NMHC concentration measured 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 pollutants formation has been evaluated. Results reveal that the shipping source is potentially one of the most important contributors to the Secondary Organic Aerosol formation potential despite the low contribution of this factor to NMHC concentration.

The impact of the lockdown due to Covid-19 is clearly visible on all sources and especially on the traffic source. The contribution of this source has decreased by a half during spring 2020 in comparison with other seasons.

A comparison of these results with emission inventories should be useful to evaluate their accuracy for a better understanding of the atmospheric pollution occurring at Marseille.