Volatile Organic Compounds shipping emissions observed in an industrial harbour of northern France

Among the regulated sources of pollutants, shipping has a significant contribution to NO_x and SO₂ global emissions ^1–3. The international maritime transport regulation was updated in 2020 lowering the sulphur content in marine fuel globally from 3.5% to a maximum of 0.5% (m/m). Specific Sulphur Emission Control Areas have been established where the emissions of sulphur are further restricted, such as the Channel, between France and the U.K. However, other pollutants such as Volatile Organic Compounds (VOC) or Particulate Matter (PM), are not regulated in terms of shipping emissions. VOCs are of particular importance in the atmospheric chemistry processes, especially because of their role in the formation of ozone and as precursors of secondary PM in the vicinity of densely populated coastal areas ⁴. This raises the question of which VOC are emitted by ships under these new emission standards, what their emission rates are and what their impact on air quality is? Only a few studies considered the speciation of VOC emitted by ships ⁵, yet those data are crucial for reliable gas-phase atmospheric chemistry modelling and correct impact assessment. Our study presents the analysis of a VOC dataset collected during an intensive one-month field campaign in the harbour of Dunkirk in northern France, the third largest French port. The observations were conducted on a site near ferry and cargo terminals and provided high temporal resolution measurements of VOCs, using a PTR-ToF-MS, alongside many other parameters (meteorology, particles, gases). Data analysis allowed the identification of more than 65 plumes from different ferries, based on a methodology that relies on favourable meteorological conditions, port office entries and tracers like SO₂. Firstly, Emission Factors (EFs) have been calculated, providing an estimate of the relative amount of a pollutant emitted relative to CO₂. For species like SO₂ or CH₄, our results were consistent with the EMEP emission inventory of 2021 (De Lauretis et al. 2021), however, some VOCs displayed large differences compared to ship exhaust determined EF within the EU/SCIPPER project ⁷. As an example, the median EF of benzene ions (C₆H₆.H⁺) was 27.87 mg/kg(fuel) versus 5.31 mg/kg(fuel) for SCIPPER, whereas toluene (C₇H₈.H⁺) was 23.37 mg/kg(fuel) versus 0.49 mg/kg(fuel) for exhaust measurement. Secondly, Positive Matrix Factorization has been applied to the dataset to investigate a shipping chemical profile of VOC that will allow us to calculate the contribution of shipping emission to the total VOC concentration in such harbour area.

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