Harbours are important hubs for economic growth in both tourism and commercial activities. They are also an environmental burden being a source of atmospheric pollution often localized near cities and industrial complexes. The POSEIDON project investigates the impact on air quality of four major harbours in the Adriatic/Ionian Seas, using a common state-of-the-art methodology based on emission inventories, numerical modelling and experimental results that will produce comparable information useful to plan future actions and controls of emissions in the Adriatic/Ionian macroregion. Expected Results: • ASSESSMENT OF AIR POLLUTION IMPACTS IN OF FOUR HARBOURS OF THE A-I SEASAn integrated methodology based on an emission inventories methodology, numerical models and experimental data has been developed and applied to four port-cities of the Adriatic/Ionian area. Emissions of particulate matter (PM2.5 and PM10) and nitrogen oxides are comparable, at municipality level, with those of road traffic. The impacts of ship traffic on PM2.5 and PM10 concentrations are variable between 1% and 8% and are larger (between 6% and 22%) on ultrafine particles number concentrations (small particles with diameter less than 200 nm). Impacts on gaseous pollutant concentrations (NOx and SO2) are 3-5 times larger than that on PM2.5 and PM10. • TECHNICAL REPORT ON THE IDENTIFICATION OF ENVIRONMENTAL POLICY GAPS AND PROPOSAL OF FUTURE COMMON MITIGATION STRATEGIES AND ACTIONS FOR THE ENVIRONMENTAL MANAGEMENT OF HARBOURS OF THE ADRIATIC-IONIAN SEASUltrafine particles (lower than 200 nm in diameter) are currently not considered in European legislation, however concentrations of such particle sizes are a better metric for evaluating the impact of maritime activities on atmospheric aerosol and for monitoring the inter-annual trends in the future. Legislations to curb ship emissions address mainly SO2 emissions (use of low-Sulphur fuels). This has a positive effect also on particulate matter emissions, however, limited or negligible effects are observed on other pollutants (e.g. metals, polycyclic aromatic hydrocarbons, black carbon) that are important for their potential impact on environment (health, climate and ecosystems). Impact of pollutants released in harbor-related activities (hoteling, loading, unloading of ships) represent an important share of the impact of maritime activities on air pollution. Development and application of guidelines and legislations specific for logistic management of harbors could be important for local air quality in port-cities.• COMMON PRESENTATION OF RESULTS IN TWO INTERNATIONAL CONFERENCES The Project results were presented to and discussed within the scientific community at two International Conferences: 2 presentations at the 17th International Conference on Aerosol Science and Technology (ICAST 2015, Lisbon 16-17 April 2015) and 3 contributions at the European Geosciences Union General Assembly (EGU2015, Wien 12-17 April 2015). Moreover, presentation of a methodology on air quality multi-model ensembles, used for the POSEIDON purposes, at the 34th International Technical Meeting on Air Pollution Modelling and its Application (ITM 2015, Montpellier, France). These are important steps to raise awareness on maritime-related atmospheric pollution and to promote and consolidate a network of communication between research institutions, local governments and the public.