## 1 Introduction
Depending on the measurement period and on the geographical area, in Europe the average ambient NO\({}_{2}\) and PM\({}_{10}\) concentrations associated with shipping emissions ranges in 12-107 \(\mu\)g/m\({}^{3}\) and 2-50 \(\mu\)g/m\({}^{3}\), respectively. In urban areas close to population clusters, such as Taranto and Naples, ship emissions led to several exceedances of the NO\({}_{2}\) annual limit. The SO\({}_{2}\) concentrations measured in different case studies have instead relatively low value, as a consequence of the mitigation strategies which regulated the SO\({}_{2}\) ship emissions in EU harbours from January 2010 (MARPOL Annex VI and the Directives 2005/33/EU and 2012/33/EU). For example, [PERSON] et al. [19] performedSO\({}_{2}\) concentration measurements from August to October 2009 and 2010 at an automated monitoring station placed on a cruise ship following a fixed weekly route in the Western Mediterranean. They found an average daily mean concentration decrease of about 66% in all the analysed EU harbours after the implementation of the aforementioned Directive. [PERSON] et al. [20], using numerical simulations, found for the port of Brindisi (South-East Italy), a significant SO\({}_{2}\) concentration reduction up to 60% in the summer period of the year 2012. Brindisi port city is one of those included in the CESAPO project (Contribution of Emission Sources on the Air quality of the Port cities in Greece and Italy) of the European Territorial Cooperation Programme Greece-Italy 2007-2013 and in the POSEIDON project (Pollution monitoring of ship emissions: an integrated approach for harbours of the Adriatic basin) of the MED program 2007-2013. Relevant findings from field experimental champaigns carried out in the frame of the CESAPO project have been documented in [PERSON] et al. [21] and [PERSON] et al. [22]. These studies highlighted the difficulty of identifying the impact of ship sources in complex urban-industrial-port scenarios and open up to the application of integrated methodologies in which numerical modelling is beneficial to the interpretation of chemical analyses. Focusing on chemical characterization only, there exist methods based on the evaluation of monitoring data. This has the advantage of being simple with a low impact of mathematical manipulation in the data treatment. In addition, statistical methods can be used as complementary to other approaches to guarantee robustness to findings. One of the main differences between several approaches is the degrees of knowledge required about the pollution sources. Chemical mass balance (CMB) can be performed when the changes of the source profiles between the emitter and the receptor may be considered minimal and secondary aerosols must be included not as components of emission sources profile but as single chemical compounds. Multivariate methods (e.g., Absolute Principal Component Analysis, Positive Matrix Factorization, Factor Analysis) may contemplate a mixture of emission sources, as opposed to clearly independent source profiles [23; 24]. A different approach is based on Chemical and Transport Models (CTMs). These models include the description of the main physical and chemical processes involved in pollutant transport and transformation and allow the prediction of air quality at various spatial and temporal scales, as well as of future scenarios. Modelled concentrations are influenced by model formulation [25; 26] and by the input emissions. [PERSON] et al. [27] assessed the accuracy of three different commonly used ship emission inventories, confirming that the air pollution levels in the Mediterranean area are significant, but strongly dependent on the applied inventory. Source apportionment tools can be implemented in numerical models [28] and they can be used in combination with receptor models [29].