Modeling of air pollution due to marine traffic in Marseille

Marine traffic is constantly increasing and is unlikely to decrease in the years to come. However, merchant and tourist ships still use fuels with a high pollutant content, particularly in the Mediterranean sea where regulations are more flexible than those applied in northern European waters. The pollutants of interest in this work, which include particulate matter (PM10, PM2.5), NO2, SO2 and ozone, are responsible for respiratory diseases such as airway irritation, cardiopulmonary and lung cancers. The aim of this study is to estimate the impact of maritime traffic on air quality in Marseille in case of high port occupancy. The same ship traffic emission scenario will be studied under a series of typical meteorological conditions selected on the basis of a statistical seasonal analysis. This approach therefore differs from studies based on annualized ship traffic scenarios, which do not capture worst-case pollution. In order to do so, we have parameterized the numerical weather forecasting model WRF (Weather Research and Forecasting) that allows the inclusion of chemistry and atmospheric transport equations. The relative difference in concentration between a situation with and without ship traffic allows us to evaluate the influence of ships on air quality. The results show an average ship contribution of between 1.5% and 5.7% for PM2.5, with some local maximum of about 25% near the port. Contribution levels for gaseous species are much higher, with values reaching 40% for SO2 and 80% for NO2. The analysis of various meteorological conditions has highlighted a significant influence of wind speed and sea-land breeze dynamic on ship contribution.