Impacts of shipping emissions on air quality: emission factors and PM source apportionment in the coastal city of Toulon, France

Maritime traffic can have a significant local impact, particularly in port areas during the docking and undocking phases. Air quality measurements conducted in certain port cities show that ship emissions are quantitatively comparable to those from road traffic and are contributing to a significant deterioration of air quality. This pollution is now recognized as a real societal problem and a proven danger for human health. Since the reduction of sulphur content in ship fuels in 2020, only few studies have been carried out to analyse in detail the contribution of shipping to urban pollution.

A month-long measurement campaign was carried out from August 24 to September 21, 2021, in the port of Toulon on the French Mediterranean coast. Particle concentration, size distribution, and chemical composition as well as gas concentrations were measured using state-of-the-art instruments such as Scanning Mobility Particle Sizer (SMPS, TSI), High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS, Aerodyne), Multi-Angle Absorption Photometer (MAAP, Thermo), Gas Concentration Analyzer (G2401, Picarro), Optical Particle Counter (OPC, Grimm), Condensation Particle Counter (EnviCPC100, Palas), Aethalometer (AE33, Magee) and various gas analyzers (100E, 200E and 400E from Teledyne).

In this study, the emission factors (EFs) for pollutants emitted from shipping were determined using a carbon mass balance approach. A total of 50 exhaust plumes was identified and quantified.

In addition, the organic fraction of the particles measured by HR-ToF-AMS was used to populate a source apportionment model based on positive matrix factorization (PMF) method.  The source deconvolution was performed for mass spectra with mass/charge ratios (m/z) ranging from 12 to 256 with a time step of 1 minute. Besides, mass spectra derived from docked ferries were used as constraining profiles. The model has been supplemented with spectra from the literature, in particular hydrocarbon-type and cooking-type organic aerosols. These features enhanced the deconvolution process, enabling emissions associated with cooking activities, road traffic and shipping to be distinguished. Ancillary measurements such as meteorological data, particle number, black carbon, and gaseous pollutants were used to underpin the physical accuracy of each organic aerosol factor in the source apportionment model. Finally, an eight-factor solution was chosen: three organic factors were associated to shipping, a hydrocarbon-type organic aerosol (HOA) associated with traffic exhaust emissions, a cooking-type organic aerosol (COA), a less oxidized organic aerosol (LOOA), a more oxidized organic aerosol (MOOA) and a last factor of intermediate oxidation.

The results of this analysis underscore the significant influence of maritime emission on urban pollution in the port area of Toulon.