Mobile mapping of PM and PNC in a Baltic Sea harbour city: spatio-temporal variability and local ship-related emission events

Ship emissions are an important sources of atmospheric pollutants in coastal regions, yet their spatio-temporal variability in harbour residential areas remains poorly characterized. This study assessed ambient PM and particle number concentration (PNC) in the Baltic Sea harbour city of Warnemünde–Rostock (Germany), where maritime and touristic activity occur in close proximity to residential areas. A stroller-based mobile platform measured PM, PNC, lung-deposited surface area, black carbon (eBC) and ozone during 56 repeated surveys covering 238 km over 14 days, complemented by rooftop stationary PM monitoring. For campaign-wide analysis, the common 3.76 km route was divided into 20 m segments. Walk–segment medians and 90 th percentiles were used to distinguish recurrent spatial patterns from isolated plume encounters, and predefined micro-environments were compared using walk-specific zone statistics. Whole-survey median PNC ranged from 2.4 × 10 3 to 1.2 × 10 4 cm -3 , while short-duration peaks exceeded 2.4 × 10 5 cm -3 . The strongest campaign-wide upper-tail hot-spot occurred along the Seepromenade during a temporary festival. Among maritime locations, the Warnow ferry terminal represented the clearest recurrent hot-spot, whereas the cruise-terminal vicinity showed episodic enhancements dependent on vessel activity, wind direction, and other factors. During the unfavorable downwind conditions, the high PNC plume peaks reached the urban and residential route sections. In contrast, PM 2.5 varied only narrowly among the predefined microenvironments, while stationary daily PM 2.5 remained generally low. Repeated high-resolution mobile monitoring therefore provides essential complementary information to fixed-site measurements by resolving short-lived plume encounters and fine-scale spatial concentration gradients and supports targeted mitigation measures such as ferry electrification and greater use of shore power.