A numerical approach to assess air pollution by ship engines in manoeuvring mode and fuel switch conditions

Due to increasing worldwide trade, transportations of goods through seaports have been gradually growing in the past years; harbours are main centres of economic activities, with unavoidable consequences on the air quality degradation and human health of many urbanized ports. This study provides a methodology to assess the impact of pollutant emission from marine engines on ambient air quality of the coastal areas. The environmental pollution from sea traffic was evaluated by assessing the production and atmospheric dispersion of exhaust emissions produced by ship engines in manoeuvring mode and in fuel switch conditions from heavysulphur residual fuel oil to low-sulphur distillate fuel oil. Specifically, this study analyses the emissive behaviour of merchant ships, equipped with large size diesel engines and transiting in the port of Naples, which is located very close to the densely populated urban centre. The spatial distribution of the air pollutant concentrations was calculated with a specific dispersion modelling approach, delivering significant data about the environmental impact of merchant ship emissions on the coastal urban area. The NOX, PM and SOX pollutant concentrations estimated with this methodology were also compared with pollution levels measured in an experimental monitoring campaign performed in the port of Naples. Estimated concentration levels were lower than measured values because the latter were affected by other anthropogenic emissive sources adjacent to port area, above all exhaust emissions from the road transport sector. Both the calculated and measured concentration levels over coastal area were below the European Limit Values.