Ship emissions are a major cause of global air pollution and have a significant impact on climate and human health. To reduce emissions and improve air quality, a number ofseveral so-called sulphur emission control areas (SECAs) have been established worldwide to further improve air quality in densely populated coastal areas and preserve vulnerable ecosystems. Consequently, ships in SECAs are only authorized to operate on low-sulphur fuels or use exhaust after treatment devices such as exhaust gas scrubbers. To comply with these regulations at sea, sophisticated measurement systems are needed. and present hIn this paperere an approach to remotely detect and characterize ship exhaust plumes through on-board measurements from a research vessel in the Baltic Sea is presented. The ship exhaust plumes are detected by particle number concentration and their size distribution through CPC and SMPS+CPC measurements and qualitatively analysed by on-line single-particle mass spectrometer (SPMS). Passig et al (2020) showed that the ionization method using KrF excimer laser with 248 nm wavelength, also used in this study, exhibits high sensitivity especially for iron but also for other transition metals. In particular, this high sensitivity of the measurement method to health-relevant metals, which are contained in PM from ships with exhaust gas scrubbers and thus serve to distinguish the fuels used, is exploited. The method of SPMS and the device used here are described in more detail in the work of Li et al (2011) and Passig et al (2021). Essentially, single particles in a size range of 0.2 - 2.5 µm can be detected and analysed. In contrast to gas phase measurements, a measurement by SPMS can easily be performed from several kilometres distance in land-based measuring stations, but these measurements are strongly dependent on wind direction (Passig et al, 2021). To overcome the dependency on wind direction, the measurements for this study were performed on board the German research vessel Elisabeth Mann Borgese. The plumes of passing ships could be recorded and analysed from a distance of several kilometres. As an example, a single event is listed in Figure 1, which suggests the use of HFO in conjunction with an exhaust gas scrubber. These measurements show that SPMS can be a powerful tool for ship exhaust monitoring. This project was funded by the DFG (German Research Foundation) – 471841824 and by dtec.bw – Digitilization and Technology Research Center of the Bundeswehr (project LUKAS). dtec.bw is funded by the European Union – NextGenerationEU.