## 1 Introduction  
Directive 2014/94/EU requires European Union (EU) ports that are part of the core Trans-European Network for Transport (TEN-T) to provide the facilities to enable alternative fuel use by the end of 2025. Significant port investment is needed to accomplish this Directive; especially to provide on-shore electricity supply (Cold Ironing (CI)) for vessels during berthing and access to Liquefied Natural Gas (LNG) refueling points. Despite the investment required, the current European regulation does not oblige vessel operators to use them (Directive 1999/32/EC, Directive 2005/33/EC). Thus, it can be affirmed that CI and LNG might not be used, even if the facilities exist. Since their capacity to abate port pollution relies on the willingness of vessel operators (the penetration rate) the concern about \"guesstimates\" for the ports [1] is shared by all geographical zones where the use of sustainable solutions in port is governed by less strict legislation. The uncertainties about the CI and LNG penetration rates for vessel operators open up an interesting discussion, not only about the expected effectiveness of these measures to mitigate port pollution [2; 3; 4] but also about who should pay for it. The answer is not self-evident [1; 5] since the benefits of their use are related to society and the environment. Thereby, some of key investors (the vessel operators) do not necessarily obtain economic benefits from them. This attitude contrasts with the EU treatment of other transport modes, where the \"polluter pays\" and \"user pays\" principles are consistently applied through the internal ization of external costs via taxes and charges collected in European Regulation (Directive 1999/62/EC amended by Directive 2011/76/EU, and currently affected by the proposal to amend COM (2017) 275 for road transport). From an environmental perspective, the European regulation has been more restrictive and efficient for load transport by road than maritime transport [6]. Thus, the traditional green label for Short Sea Shipping (SSS) in the domestic traffic is currently under discussion [6; 7], since its current technical limitations are far from meeting the emission standards required by the EU for the land transport (Euro VI standards) [8; 9]. In light of the foregoing, the performance of port mitigation alternatives is particularly interesting for SSS [7; 10]. The intensity of this type of traffic (high number of calls and sailing close to the coast), along with its energy requirements during berthing, have led to the identification of SSS vessels as the largest beneficiaries of CI [3; 5; 11] and LNG [12]. In this regard, [PERSON] and [PERSON], 2020 [10] highlighted the evidence of the environmental benefits obtained in SSS from the combination of technical and operational initiatives of shipping companies adopted as complementary measures to the normative efforts of the authorities. However, a number of authors have raised concerns about this type of traffic's mitigation practices in port: additional times are required for CI connection that could make SSS competitiveness unfeasible for short calls [13; 14]; the islands are frequently involved in SSS activity and their electricity grids are mainly supplied by burning oil, leading CI to be a poor sustainable alternative [5]. Beyond the Sulfur Emission Control Areas (SECA) and Emission Control Area (ECA) zones, defined in Annex VI to MARPOL where SO\({}_{x}\) and NO\({}_{x}\) emissions are restricted during sailing, regulatory pressure has been increasing in ports. Hence, in the EU, since 2010 Community ports have demanded a maximum limit of 0.1% sulfur by weight for marine fuels used by inland waterway vessels and ships at berth (Directive 2005/33/EC; amending Directive 1999/32/EC). However, emission --equivalent to those that would be achieved through the limits on sulfur in fuel--can be authorized through the use of abatement technologies.