The International Maritime Organization capped the fuel sulfur content of marine fuels outside ECA zones to 0.5 % in 2020. Consequently, either low-sulfur fuels or additional exhaust gas cleaning devices for the reduction in sulfur dioxide (SO2) emissions became mandatory. Although a wet scrubber reduces the amount of SO2 significantly, there is still a need to consider the reduction in particle emissions and organic pollutants. We present data on the particle removal efficiency of a scrubber regarding particle number and mass concentration with different marine fuel types, viz. marine gas oil and two heavy fuel oils (HFOs) with sulphur contents of 1.3 % and 2.4 %, respectively. An open-loop sulfur scrubber was installed in the exhaust line of a marine diesel test engine. Fine particulate matter with diameters below 2.5 µm (PM2.5) was comprehensively characterized in terms of its physical and chemical properties. The wet scrubber led up to a 40% reduction in particle number, whereas a reduction in particle mass emissions was not generally determined, as with HFO 2.4 % sulphur even a slight increase was observed. (Table 1). Furthermore, a shift in size distribution to larger particle diameters occurred after the scrubber when the engine was operated with the HFOs. The behaviour of particle mass concentrations could be related to an increase in sulfate particles with HFO 2.4 %, whereas soot particles did decrease slightly. However, for considerable reduction of respirable particulate matter the sulfur scrubber is not sufficient and one would need an additional filter system. Combining the scrubber with a wet electrostatic precipitator as an additional abatement system indeed showed a reduction in particle number and mass emission factors by >98%. Particles also transport organic pollutants, among them Polycyclic Aromatic Hydrocarbons (PAH), crucial for their carcinogenic and mutagenic potential. Online measurements with the Single Particle Mass Spectrometer revealed for HFO 2.4 % sulfur, that the number of detected soot particles decreased after the scrubber, but the number of PAH containing particles remained constant. With a load of 20 kW, this number even increased. Another important question is the transfer of PAH from the gas/particle phase of the exhaust to the aqueous phase when the exhaust pass the wet scrubber. With a new online instrument using a membrane inlet for extracting organic compounds out of the water into a mass spectrometer, we could clearly detect 2- and 3-ring PAHs in the wash water going out the open-loop scrubber. Concluding, the application of a wet scrubber for the after-treatment of marine fuel oil combustion will reduce SO2 emissions, but it does not substantially affect the number and mass concentration of respirable particulate matter. Complete removal of these particle emissions affords the inclusion of additional abatement systems. Moreover, Polycyclic Aromatic Hydrocarbons are still present in the exhaust after the scrubber and are partially transferred to the wash water, which would be introduced back in the ocean when using a open-loop system. This work was supported by the Federal Ministry for Economic Affairs and Climate Action by the project SAARUS (grant number 03SX483D). The research is also supported by dtec.bw – Digitalization and Technolgy Research Center of the Bundeswehr [project LUKAS and MORE]. Dtec.bw is funded by the European Union – NextGenerationEU. Support by the companies Saacke, RVT, Gea, AVL, and Sult is gratefully acknowledged.