Hydrocarbon, PAH and PCB emissions from ferries: A case study in the Skagerak-Kattegatt-Öresund region

Hydrocarbon speciation measurements have been carried out on board two passenger ferries (medium speed, four-stroke diesel main engines) operating in the Skagerak-Kattegatt-Öresund region. Average emission factors for 20 light-weight hydrocarbons (C2–C6), 12 medium-weight hydrocarbons (C6–C12), 23 polycyclic aromatic hydrocarbons (PAH), 7 polychlorinated biphenyls (PCB) and hexachlorbenzene (HCB) were determined for a situation with varying engine loads and a short service route (MS Aurora, Helsingborg-Helsingor) and a case with a longer service route and more constant engine loads (Stena Danica, Goteborg-Fredrikshavn). In general, ethene, propene, isobutene, benzene and C9---C12 alkanes dominated the hydrocarbon compositions measured, although their relative proportions differed between the two ferries. The PCB emissions measured were relatively small which is probably a reflection of the low Cl content in the fuel and gas oils used. The levels of PAH detected appear, however, to be of significance; the total PAH group accounted for ca. 1 % of the total hydrocarbon emission. It is roughly estimated that ferry traffic in the Skagerak-Kattegatt-Öresund region accounts for ca. 5 t PAH and ca. 1 kg PCB per year. In line with previous estimates of marine emissions, NOx emissions from the ferries were quite significant and this represents an important source in the study area. Since average hydrocarbon emission rates were only ca. 1 % of the NOx emissions, tropospheric ozone formation will be more dependent on the NOx emissions irrespective of the composition of the emitted hydrocarbons. In addition, the low HC/NOx ratio in the emissions also indicates that the possible contribution of ferry traffic emissions to hydrocarbon measurements at coastal stations is not very significant.