Comparison of the impact of ships to size-segregated particle concentrations in two port cities in northern Adriatic Sea

The impact of shipping and port activities to air quality in coastal area is an important topic for sustainable development and for port management, because of the environmental pressures and potential adverse effects on health. Quantification of port-related emissions and their role in atmospheric pollutant concentrations is a challenging task addressed with many approaches in recent years, especially in congested coastal regions (i.e. Adriatic Sea). High temporal resolution stationary measurements of aerosol particles, taken downwind of port area, have been proved to be a valid method to provide an accurate assessment of ship traffic impact on local scale (Merico et al., 2016). Furthermore, studies of the impact of shipping to particles of different sizes (including nanoparticles) are still relatively scarce. In this work particle number and mass size distributions are investigated, correlating them with meteorological parameters (i.e. wind speed, wind direction) and vessel traffic data in two Adriatic port-cities (Venice, Italy; Rijeka, Croatia). Relative contribution of ship traffic to particle of different sizes are estimated and compared to previous studies (Merico et al., 2016; Donateo et al., 2014; Contini et al., 2011) done with the same apportionment approach. Total particle number in the range 0.01 - 0.25 ?m and particle number size distributions in 31 size channels (range 0.25 - 31 ?m) are detected at 1-minute resolution by a Condensation Particle Counter (CPC, Grimm 5.403) and an Optical Particle Counter (OPC, Grimm 11-A), respectively. Three main size ranges are individuated in both cases: nanoparticles (D<0.25 ?m); fine particles (0.251 ?m). Concentrations are larger in Venice compared to Rijeka. Number size distributions are almost superimposable for Venice and Rijeka, with the highest value of about 10,000 #/cm3 at 0.25 ?m, decreasing up to a few particles of diameter higher than 0.6 ?m. Instead, the size distributions in mass are partially similar showing two peaks at similar diameters (about 0.3-0.4 ?m and 2-3 ?m). Daily patterns of nanoparticles show two peaks at morning hours and (less evident) in early evening at both sites. Also, the effect of the dynamics of the boundary-layer influences daily pattern of larger particles (D>0.25 ?m) mainly in Venice. Finally, estimated contribution of shipping to particle of different sizes is relatively larger for nanoparticles (> 7%) compared to ultrafine and coarse ones (up to 2%) in Venice (Fig. 1). Instead, in Rijeka the contribution is visible on nanoparticles (up to 2%) but it is not discernible on larger particles. Results should be evaluated considering that Rijeka is characterised by a lower ship traffic intensity and by smaller ships compared to Venice.