Concentrations and origins of ultrafine particles at a major European harbor

The maritime transport sector poses significant air quality concerns, particularly in nearby cities. Ultrafine particles (UFP, diameter < 100 nm) are of particular concern due to their potential health impacts. This study measured particle number concentrations (PNC), size distributions (PNSD), and other pollutants including particulate matter (PM), nitrogen oxides (NO X ), black carbon (BC), sulfur dioxide (SO 2 ) and ozone (O 3 ), organic markers and trace elements at a major European harbor and an urban background (UB) location. The average PNC at the harbor was 1.8-fold higher than at the UB, with particularly marked differences in the Aitken mode (2.4-fold higher). NOx levels were 10.5-fold higher at the harbor, and NO 2 , NO X and BC concentrations were 2.0 to 2.9 times greater compared to the UB site. SO 2 concentrations were also 1.7-fold higher at the harbor. Two distinct types of PNC peaks were observed: daytime peaks with high Aitken mode particles likely linked to transit ship emissions, and late afternoon/nighttime peaks with higher nucleation mode particles likely linked to thermal power plant emissions, docked cruise ships, and vehicular traffic related to ferry boarding. Source apportionment of PNC-PNSD through Positive Matrix Factorization (PMF) identified four key contributors to PNC at the harbor: Regional recirculation (9 %, modes: 100 nm and 35 nm), Nucleation (30 %, mode: 18 nm), Coastal background (22 %, mode: 75 nm), and Ship transit (33 %, mode, 35 nm). Concentrations of Ti, V, Cr, Ni, Cu, Zn, As, Sb, Pb and Na in the quasi-UFP range were more than twice at the harbor compared to the UB. This study provides insights into UFP concentrations and their sources within a major touristic and commercial harbor, highlighting the complexity of identifying specific contributions from various UFP emission sources in large harbors. • PNC, PNSD and chemical composition of quasi-UFP inside a harbor were investigated • PNC at the harbor was 1.8-fold higher than urban background • Observed overall unimodal PNSD in the harbor, with a size mode at 25 nm • Observed nocturnal Nucleation mode peaks from docked cruises and thermal power plant • Detected ultrafine Ti, V, Cr, Ni, Cu, Zn, As, Sb, Pb and Na particles