Air Pollution from Ships - Emission Measurements and Impact Assessments

Sammanfattning: Environmental impact and air pollution from ships have received increasing attention the last decades. Due to combustion characteristics of typical marine engines and a wide spread use of unrefined fuel, the global fleet emits significant amounts of SO2, NOX and particles to air. Impact assessments and information on emitted amounts are important inputs to decision-making in regulation development and also for ship designers who aim at environmentally improved designs. In order to assess the impacts caused by ship emissions to air, information on ships’ activities in an area or the corresponding fuel use is essential. In combination with an emission factor that state the mass of an emitted pollutant related to either the work produced by ship engines or the mass of combusted fuel, the total emitted mass of a pollutant is established. Ship engines are diverse and the emission factors are insufficiently quantified for certain operational modes and specific pollutants which makes assessments difficult. Measurements on-board ships were thus conducted in order to determine emission characteristics during manoeuvring periods and for engines operating on fuels of different qualities. The measurement studies comprised three engines and focussed on emissions of particles and NOX. Elevated levels of numbers of small particles (0.30-0.40µm) were observed during manoeuvring periods and from combustion of marine distillate oils. Sizes <0.30µm were not covered by the study. The size distribution of particles is potentially important in impact assessments since there are indications that fine and ultrafine particles are associated with higher health risks than coarse particles. The particle mass was reduced by half from a shift from a heavy fuel oil with 1.6% sulphur content to a marine gasoil with 0.03% sulphur. The results from the impact assessments point in favour of the abatement technologies selective catalytic reduction (SCR), shore side electricity (SSE) connection and the use of fuel with low sulphur content in a local and regional cost benefit perspective. The SSE seemed beneficial also from a shipowner perspective. SCR was also analysed in a life cycle perspective and it was concluded there were overall benefits from its use for all impact categories except global warming.