# Forecast Analysis of Pollutant Emissions of Cruise Ship Routes in Western Mediterranean
## 2 Literature Review  
The key element of cruise shipping is the cruise itinerary system. A cruise itinerary is composed of the sum of the ports of call plus one or two homeptors, depending on whether the itinerary is closed or open type, respectively. Once the cruise vessel is deployed in a given destination region, it will sail in regular itineraries for the duration of the season. From the network analysis point of view, a cruise itinerary is composed of nodes (ports) and edges or links (shipping routes) between pairs of nodes due to the activity of ships. There are several techniques to exhibit network connectivity in maritime transport. The use of SNA (Social Network Analysis) and centrality measures to analyse shipping networks have been applied by several authors. A wide range of works has applied centrality measures as tools to analyse shipping networks [12; 13; 14]. Cruise shipping networks have also been analysed through centrality measures; for instance, [PERSON] et al. [15] developed a numerical analysis of hub ports in cruise shipping to explain the regional dynamics of the regional cruise industry; [PERSON] and [PERSON] [16] used network measures and random network models to analyse the structure, characteristics, and connectivity of the Asian-Australasian cruise shipping network; [PERSON] et al. [17] investigated structural changes in the cruise network by ship size in Northeast Asia by combining network science methods and data on cruise ship movement; and, [PERSON] et al. [18] conducted research into cruise port interconnections and their influence on the operation of the entire Caribbean port network. The gas emissions of cruise ships can be associated with three different operation phases: navigation, manoeuvring, and mooring. The navigation phase evaluates the gas emissions derived from ships' activities at sea. The manoeuvring phase corresponds to the gas emissions during the approach to and departure from the cruise terminal. The mooring phase includes the gas emissions of hoteling and embarking/disembarking of passengers. In each phase, the energy requested by the main engine/s and auxiliary engine/s is different; therefore, the emissions have large variations. The impact of ship emissions is on a global, regional, and local scale, respectively. The first and second scales mainly concern emissions during the navigation phase, and the third concerns the manoeuvring and mooring phases. This research focuses on the navigation phase, considering the regional impact of emissions associated with the main cruise routes in the Western Mediterranean. Following [PERSON] and [PERSON] (2019), two parameters must be considered when evaluating air emissions due to maritime transport, namely, the amount of gas emissions and where they are produced. Generally, there are two different approaches to estimating emission inventories: top-down (fuel-based) and bottom-up (activity-based). The fuel-based approach is one of the top-down approaches for creating ship exhaust gas emission inventories, in which the amounts of ship gas emissions are calculated based on the total fuel consumption and fuel emission factors. In a top-down approach, total emissions are calculated without considering the vessels' characteristics. The accuracy of fuel-based approach total emissions is limited by uncertainty in global estimates, and representative bias of spatial proxies limits the accuracy of emission assignment ([PERSON], 2018). The bottom-up approach uses technical information about ships and ships' activities to estimate ship gas emissions. This approach is much more accurate, but significant efforts need to be made for data collection and analysis ([PERSON], 2018). The ship activity-based approach has been applied in a wide range of works to assess the emission inventory at different phases of ship operation ([PERSON], 2018; [PERSON], 2018; [PERSON], 2018).