## 1 Introduction
Therefore, the sulfur limitations collected in the Directive were met through different operational solutions (e.g., MGO fuel types 0.1% sulfur, HFO fuel with scrubber use or LNG as fuel, etc.). Despite this restriction, the Commission in 2006 recognized that the regulation established up to that date had been insufficient to maintain port air quality. Consequently, it recommended shore-side electricity (CI) for use by ships at berth in Community ports (Recommendation 2006/339/EC), since it provides additional benefits such as noise reduction, which is especially important for ports situated near residential areas. The COM 2013(295) highlighted the need for stricter requirements on environmental performance in ports. In a further step, Directive 2014/94/EU forces Member States to ensure not only shore-side electricity supply (CI) for vessels but also available refueling points for LNG by 31 December 2025 in TEN-T Core Network ports. In parallel, EU Regulation (2017/352) seeks to define the common criteria (European Commission and Member States jointly) for voluntary environmental charges in port. Additionally, this Regulation gives ports the freedom to make changes in order to promote the sustainable use of their own infrastructures. The provision of LNG and CI services involve significant port investment; nonetheless, CI is often presented as a feasible solution for emissions mitigation [1; 2; 3; 4]. This is so, even when CI's high dependence on on-shore energy (the vessels' electricity consumption is met by plugging them into the on-shore electricity network during berthing time). The main advantage of CI is the relocation of the emission source far from ports where the existence of significant population centers in the port's hinterlands makes NO\({}_{x}\) and SO\({}_{x}\) emissions from vessels especially harmful, since these pollutants have a direct impact on citizens. The additional advantages of CI in contrast to other mitigation solutions are the elimination of port waste, noise, vibrations etc. Nevertheless, [PERSON] et al. [5] warned about the risk of CI use in regions that are highly dependent on fossil fuels for electricity generation (many of the islands), while [PERSON] et al. [14] highlighted the possible lack of feasibility of CI for short call traffic (lag connection times). In turn, LNG has proved to be the most suitable fuel alternative for SSS when cost, time and sustainability are jointly evaluated from the vessel operator's point of view [12]. However, methane emissions remain a weak point that penalizes the reliability of LNG as a mitigation port solution. In order to reduce the uncertainties about CI and LNG performance on the mitigation of SSS port pollutant emissions, this paper introduces a mathematical method to calculate emission savings by LNG and CI use versus traditional on-board electricity supply. The method quantifies in monetary terms the emissions savings for SSS in such a way that it permits us to assess in several routes, not only the performance of one port abatement alternative, but also to compare several systems' performance with diverse types of suitable vessels to SSS. The method has been tested through its application on three SSS routes, where ports with different electricity grids are involved: the Atlantic coast between France and Spain; the South of Spain and the Canary Islands; and interisland traffic (Canary Islands). The application case considered two different kinds of vessels for the routes: feeder and Ro-Pax vessels. The paper offers quantitative results that are useful not only for the port authorities and stakeholders involved in the case studies, but also for policy makers and ship operators who can evaluate the influence of on-shore electricity grids and vessel characteristics on the performance of the mitigation measures in port.