# Forecast Analysis of Pollutant Emissions of Cruise Ship Routes in Western Mediterranean
## 3 Materials and Methods  
The research conducted can be divided into four steps. First, identification of cruise routes in the Western Mediterranean using network analysis techniques. Second, technical characterisation of the vessels deployed on each identified route. Third, estimation of the gas emission inventory through a ship activity-based approach. Finally, forecasts of emissions were carried out considering five scenarios for the evolution of cruise traffic in the Western Mediterranean. A schematic representation of the process addressed during the research carried out is shown in Figure 1.  
The input data to perform the research were the time series of cruise ship calls in 2019 of 10 Mediterranean ports. The year 2019 was selected as a reference year to conduct the research because it is the last available with high-performance indicators for cruise activity. The aim of the research is to provide an estimation of gas emission inventory not affected by the restrictions imposed by the pandemic during the period of 2020-2022. Specifically, the database is composed of the cruise ship calls registered in the ports of Barcelona, Gibraltar, Ibiza, Katabo, Livorno, Mahon, Malaga, Palma de Mallorca, Santorini, and Valencia. The data were retrieved from the Port Authorities' websites (Santorini, 2019; Santorini, 2020; Santorini, 2020; Santorini, 2020; Santorini, 2020). For each call registered, the database is composed of the vessel name and the last and next port of call. The data were unified to create a common database with all the calls. In the first step, cruise routes in the Western Mediterranean were identified through the application of network analysis. The investigation of network connectivity addresses the association between nodes (cruise ports) in a network that are connected by links between them (cruise routes). The last and next ports of call are the data necessary to obtain the nodes and links between them of the cruise shipping network. Octave software (www.octave.org, accessed on 12 January 2023) was used to calculate network parameters, and Ucinet 6.0 [41] was also used to both calculate network parameters and graphically represent the main cruise routes. Once the main routes were identified, the second step was to characterise, from a technical point of view, the cruise fleet deployed on the routes. For each vessel, the following technical parameters were retrieved: length (L), breadth (B), draught (T), gross tonnage (GT), service speed (S), type of propulsion machinery, and total output power for sailing (P). For this purpose, each vessel was characterised by searching in specialised databases, such as Significant Ships [42] or Vessel Finder [43]. A total of 158 different vessels said on the routes analysed. Six types of propulsion power plants were identified: low-speed diesel engine, medium-speed diesel engine, high-speed diesel engine, gas turbine, combined diesel engine and gas turbine (CODAG), and combined diesel engine and sails. Figure 2 shows the distribution of type of propulsion power plant among the fleet analysed. A total of 83.5% of the fleet had medium-speed diesel engines installed. In the case of the two vessels equipped with the CODAG system, the power of each engine was retrieved with the aim of estimating the emissions associated with each of them. Specifically, for both vessels, the CODAG system is equipped with medium-speed engines. For the seven vessels equipped with diesel engines and sails, the most unfavourable condition from the environmental point of view was considered; that is, sailing with the diesel engine, as the seven vessels had high-speed engines. Figure 1: Schematic representation of the research carried out. Figure 3 summarises the range of output power of the propulsion machinery of the fleet analysed. A total of 77.2% of the fleet is in the range between 10,001 and 70,000 kW. Almost all the ships analysed feature a diesel-electric propulsion form. Specifically, the propulsion power plant is equipped with several engines.