Trends of shipping impact to particulate matter in two northern Adriatic port-cities

Port-cities interested in busy shipping routes can have a significant environmental and health exposure risk to emissions related to harbour activities. However, the recent strengthening of the IMO legislation, in force since 2020, on the sulphur content in maritime fuels (from 3.5% to 0.5% in mass) is expected to curb ship emissions of sulphur oxides and particulate matter, thus reducing shipping-related mortality and morbidity. Being more harmful to health, fine particles and nanoparticles, emitted by ships' engines, could be monitored as particle number concentration (PNC), in addition to regulatory limits for PM10 and PM2.5. In this work, an integrated approach based on high temporal resolution measurements of PM2.5 and PNC was applied in two Italian harbour sites (Brindisi and Venice). Some experimental campaigns performed in different years (between 2012 and 2018) with a similar instrumental setup and statistical treatment of acquired particle concentration data, meteorological conditions and ship movements records, allowed to investigate temporal trends in shipping impact on the same areas. In addition, contribution to different particle sizes was estimated at both harbours. Inter-annual trends of estimated impacts are reported and discussed. In general terms, the contribution to PNC are 3-4 times larger than that to PM2.5. In Venice, the effectiveness of the combined application of the international legislation and local voluntary agreements was evident in lowering the primary impact of maritime transport, especially on PM2.5 at local scale, although an increase of ship traffic volume. Instead, the weight of port logistics was demonstrated by an increase of the PNC contribution in Brindisi. Finally, the size-segregated impact showed a maximum relative contribution to nanoparticles, followed by a minimum for larger diameters (between 1 µm and 1.5 µm), and a growth in the coarse size range, likely related to harbour logistics activities.