Sustainable Port Operations: Pollution Prevention and Mitigation Strategies

Abstract

This paper presents a review of current developments in port pollution prevention and mitigation. A systematic categorization of the sources of pollution in the development and operation phases of ports and terminals is first presented. The paper then considers in detail technological and regulatory measures currently being applied to limit port pollution in the operation phase. This review is combined with that of relevant academic research and aims to fill a research gap by identifying the current and emerging port pollution themes and the latest trends in measures for pollution prevention and mitigation. A comprehensive approach is taken in this review by including not only academic research but also the industry’s research and development initiatives and the regulatory authority’s legislation. This paper identifies more than thirty different technological, regulatory, or organizational measures to limit pollution, although details on company-based research and development were found to be scarce. Mitigation of greenhouse gases and air-polluting emissions is identified as the most important field of research, but it is affected by regulatory uncertainties. Further research is needed on topics such as increased alternative fuel provision, digitalization potential for sustainability enhancement, and strategies for engaging stakeholders in greening ports.

1. Introduction

The development of maritime transportation that has accompanied globalization has brought to the forefront issues related to shipping, as well as port pollution and its mitigation. This is a vast multidimensional topic that requires holistic approaches in the quest for achieving the objective of developing truly sustainable ports, often called green ports. A green port is defined in [1] as “A port that invests and encourages environmentally friendly and sustainable development and operations”. This definition encompasses an important aspect that must be taken into consideration: two phases in the port activity need to be considered so that the entire life cycle of port infrastructures is duly taken into consideration. Thus, both the development (construction phase) and the operation phase need to be considered, to which could be added a third phase, the decommissioning phase (redevelopment), although it is generally limited to specific terminals or delimited port areas. The development of entire ports, or merely a single port terminal, may occur on greenfield sites or merely involve the expansion of already existing ports or terminals. Given the wide range of activities with potential pollution consequences across these three phases of a port’s life cycle, this paper will consider only research focused on pollution arising during the operation phase of the port, as it typically spans decades and is, thus, expected to have a long-term impact on populations and the environment.

Another broader definition for a green port is given in [2] as “A port in which the port authority together with port users, proactively and responsibly develops and operates, based on an economic green growth strategy, on the working with nature philosophy and on stakeholder participation, starting from a long-term vision on the area in which it is located and from its privileged position within the logistic chain, thus assuring development that anticipates on the needs of future generations, for their own benefit and the prosperity of the region that it serves”. This definition offers additional insights as it emphasizes several aspects of high importance when promoting a green port: the need for the entire port community to work together in a cooperative manner, the importance of a long-term vision, the recognition of ports as just nodes in logistic chains, and the necessity to account for the economic development of the port’s region. Both these definitions are aligned with at least seven of the United Nations (UN) Sustainable Development Goals [3], namely, clean water and sanitation, affordable and clean energy, decent work and economic growth, industry, innovation and infrastructure, climate action, and life below water and life on land.

Another definition that brings in an additional element [4] identifies a sustainable smart port as one that “produces/uses/distributes renewable energy and integrate green and new technologies to enable the energy transition and enhance energy sustainability of ports, as well as tap into the possibility of distribution of renewable energy”. This definition includes the connection to new technologies that can transform the port into a smart system, leveraging the benefits of information technology (IT) in supporting and managing the energy transition. This is a significant and extensive element, but it falls outside of the scope of this paper.

These definitions reveal the fact that sustainability is at the forefront of ports’ concerns nowadays. This occurs because in some major ports of the Far East, between one-third and one-half of SO₂ and NOx emissions arise from port activities [5], and in major European cruise ports, ships alone pollute as much as or more than all the cars circulating in these cities [6]. Even in a smaller port, the number of annual premature deaths due to excess PM_2.5 and NO₂ exposure was estimated to be 82 and 25, respectively [7].

In relation to these aspects, it is also important to define the geographical scope of this paper as being restricted to pollution generated within the limits of the designated geographical area under the jurisdiction of the port authority, which is generally defined in national or local legal documents (laws). This geographical area nowadays often includes areas allocated to logistic activities or even industrial activities, which, thus, also need to be considered. Figure 1 shows the geographical scope of this study and the interactions between the different components of the system that constitute modern ports: maritime accesses, terminals, rail, road, and inland waterway (IWW) accesses and logistic facilities. The gray arrows indicate the navigation of the ship through the maritime accesses to ports, which in many cases may extend for several miles, implying, for example, significant volumes of emissions arising from the ship traffic, in addition to the emissions and other pollution arising when maneuvering and at berth. The terminal is also a port component that produces several different forms of pollution, as will be discussed. Finally, it is necessary to transport cargo to the port’s hinterland, represented by the black arrows. Significant sections of rail, road, and inland accesses often fall within the geographical scope of the port, and its polluting impacts need to be considered. In some cases, cargo may actually receive value-added services or be entirely processed within the port area (in industrial zones) before being carried outside the port’s limits.

The general topic of green ports has attracted significant attention in recent years. Some examples may be mentioned, such as a recent review, by a classification society and an association of ports, of pollution mitigation measures concerning emission of air pollution and greenhouse gases, which may be found in [8]. The European Sea Ports Organisation (ESPO) also published two guides on the topic of greening ports in 2012 and 2021 [9,10]. This interest of port associations is not confined to Europe, as demonstrated by the sustainability strategy development guide published by Ports Australia [11].

Academia is also active in this field of study, with several publications in recent years. One example from 2019 deals with inland and seaside sustainable transportation strategies, covering a wide range of topics [12]. Other publications on greening of the shipping industry, as a whole, typically include chapters dedicated to ports [13,14]. Port management publications also consider, nowadays, green ports [15]. There are also several publications containing literature reviews entirely dedicated to green ports [16,17,18,19]. The connections between digitalization, innovation, and sustainability were comprehensively reviewed in [20]. The perspective of strategic management on sustainability, namely, green strategies within the framework of a conservative port industry, was covered in [21].

This paper has the objective of characterizing the most common themes with regard to port pollution during the operational phase of the port, but also to cover other, less researched forms of pollution, providing a broad overview of the subject. It is also an objective to comprehensively review the measures proposed and under study for addressing the various forms of pollution. Another objective is to evaluate which themes are considered currently more important in light of the current sustainability trend and identify the most significant literature in respect of each theme. This paper also aims at taking a broad approach in the literature review by duly considering not only academic research, but also including and recognizing the important studies, technologies, and regulations contributed by the port and shipping industry. Finally, this paper also aims at reviewing the most relevant management and reporting approaches with regard to port pollution. Overall, this paper contributes to the literature by providing a general and updated review of a topic undergoing a major shift of focus towards the promotion of cleaner forms of energy.

The structure of the remaining part of this paper is organized as follows. Section 2 presents a categorization of the sources of port pollution in the development and operation phase. Section 3 describes the materials, sources, and approach used to identify the most relevant studies and papers concerning each pollution prevention and mitigation measure. Section 4 covers the results of the literature review on technological and regulatory measures and academic research on green ports, organized around pollution prevention and mitigation measures. Section 5 provides a summary and brief discussion of the materials detailed in Section 4 and examines the involvement of stakeholders in the various port pollution prevention and mitigation measures. The paper concludes with Section 6, which provides main conclusions and recommendations for further research in this field.

2. Port Pollution Throughout the Port Life Cycle

2.1. Categorization of Port Pollution Sources

This section presents a broad categorization of port pollution sources in the development and operation phases. One of the earliest and very comprehensive categorizations of port pollution sources was developed and presented in [22]. This paper moves well beyond the most common concern nowadays, which is port decarbonization [8], extending to water and land pollution. Industry practice papers such as [9] recognize also the broad nature of port pollution, while PIANC [2] divides port sustainability issues into 13 categories. Academic references on port management [13] propose nine different categories for port environmental pollution. Some other academic studies [22] are much more detailed, considering as many as 63 sub-categories. This section presents a balanced categorization comprising 18 categories, basically those of PIANC [2], with a few reorganizations and additions dictated by new topics and by a more complete range of topics: vibration impacts, light pollution, ballast water, geology, rainwater contamination, hydrodynamics, heritage, and regional planning. Furthermore, all top environmental priorities identified by ESPO in 2023 [23] are included in these categories.

The topic of port pollution involves a vast number of potential sources, active during the development and operational phases, as shown in

Table 1. Categorization of port pollution and its impacts on the environment.

	Area	Goal
1	Air Quality Management	Accommodate port operations and developments but complying with short- and long-term air quality goals for SOx, NOx, and PM.
2	Climate Change Management	Reduce greenhouse gases (GHG) directly linked to global warming: CO2, CH4, N2O.
3	Noise Impacts	Manage noise from ships and port equipment to reduce public health hazards and ecological hazards.
4	Vibration Impacts	Port operations require heavy mechanized equipment and induce road/rail traffic, harming buildings and persons.
5	Light Pollution	Floodlights and blinking vehicle lights in a night environment also have impacts in urban areas and animals.
6	Ship-Related Waste Management	Reduce discharges into the river or sea of ship-generated waste and cargo residues.
7	Ballast Water Management	Reduce discharges into the river or sea of non-treated ballast water.
8	Rainwater Contamination	Manage contamination of rain water with dry or liquid bulk cargos, including providing containment and treatment means.
9	Dredging Impacts	Promote sustainable dredging to keep ports’ nautical accesses open, clean, and safe.
10	Geology and Geological Impacts	Port development may have impacts on local geology.
11	Surface Water and Sediment Quality	Support attainable beneficial uses of resources without degrading environment.
12	Soil and Groundwater Quality	Manage historic legacies of soil and groundwater pollution while enhancing new port development with environmental quality.
13	Hydrodynamics and Sediment Transport	Port infrastructure such as quays, piers, breakwaters and channels may affect local hydrodynamics and alter sediment transport.
14	Habitat and Species Management Health	Port design and development philosophies should work in line with nature.
15	Landscape Management and Quality of Life	Minimize impacts on landscapes to correct and improve port aesthetics (colors of cranes, buildings and equipment).
16	Heritage and Patrimony Impact	Visual conflict and impact of vibration and pollution due to port on existing protected buildings.
17	Land and Water Area Uses	Long-term sustainable management of port and concessionaires expectations and compatibility with population’s expectations.
18	Regional Planning and Economic Impact	Development of ports alters and produces new flows of freight and people and puts pressure on territory (facilities, housing).

. Categories 1–8 are more relevant during the operation phase of the port (or terminal) that will typically last tens of years. These categories of impact depend largely on the port being actually in operation, while categories 9–18 (gray area) need to be considered at the outset of the development phase of the port and may condition its actual feasibility.

It is important to mention that dredging is generally necessary in the development phase (initial dredging), but will also be necessary on a regular basis during the operation phase of ports in order to re-establish water depth throughout the navigation channels and maneuvering basins if silting has occurred (periodic dredging). The extent of these works varies from port to port and has the same pollution impact as the initial dredging. As it is akin to initial dredging, it has been left out of this paper as the focus is on the operational phase of the port. However, it should be mentioned that such works generally require regulatory authority approval and need to be carried out in accordance with national and international regulations, for example, in Northwestern Europe, the OSPAR convention and guidelines for management of dredged materials [24,25].

It should be recognized that in pollution categories 1 to 5 there are three aspects that play a determinant role in prevention and mitigation of impacts. One aspect is the need to accommodate existing and increased future transport volumes while minimizing or eliminating their environmental footprint, which can be achieved by acting in the port’s modal split, favoring rail and inland waterways modes of transportation in detriment of road transportation. Another important aspect is the production of renewable energies locally, thus greening the energy sources mix. A third aspect is the capacity to bunker ships, trucks, and cargo-handling equipment with different types of low- or zero-carbon alternative fuels or electrical power, reducing not only emissions but also noise and vibration.

It is also worth mentioning that Table 1 includes two categories (16 and 17) centered on the impact of ports and terminals in the landscape: heritage and patrimony. The choice to include these impacts in this categorization was made considering that they produce significant effects in the cultural environment surrounding the port area and severely impact the populations. Finally, category 18 recognizes, in line with [26], that the development of a port contributes significantly to the socio-economic development of its region as a whole, inducing increased or new flows of freight and persons and the establishment of industrial and commercial companies, eventually grouped in logistic and industrial parks. These new activities generate their own pollution and further impact the environment.

The set of categories 9–18 is generally dealt with at the design stage through a preliminary screening (whether environmental impact assessment (EIA) is required or not). Once it is established that such assessment is needed, its scope is established, and the study is prepared, placed in public discussion, evaluated by the National Environment Agency and, eventually, approved. The development projects subject to this evaluation procedure and its details and methodologies are outlined in European Union (EU) directives [20,27,28]. This paper will not further consider these aspects and the decision process just outlined, as it concentrates mainly on the operation phase of the port and terminals.

A general approach to greener ports should also consider the need to promote climate change adaptation by preparing ports for sea level rise and increased storm surges. It is, therefore, clear that port pollution, along with its reduction, management, and mitigation, leading to a green port, is a vast research area. Most themes have been around for many years, but some additional ones have come into existence in recent years, such as certain types of air pollution and underwater noise. During the port’s operations phase, pollution mainly arises as a result of ships, cargo handling and storage, transportation of cargo to/from the port’s hinterland, and logistic/industrial activities within the port’s jurisdictional area.

Table 2. Categorization of port pollution themes according to the activity in which it occurs (X indicates that an activity has impact in a certain pollution theme).

	Ship-Side Transport	Cargo Handling and Storage	Land-Side Transport	Logistic and Industrial Activities	Impacted Medium
Air Quality Management	X	X	X	X	Air
Climate Change Management	X	X	X	X	Air
Noise Impact	X	X	X	X	Air/Land
Underwater Noise	X				Water
Vibration Impacts		X	X	X	Land
Light Pollution		X	X	X	Air/Land
Ship-Related Waste Management	X				Water/Land
Ballast Water Management	X				Water
Rainwater Contamination		X		X	Water/Land

enumerates broad types of pollution (or pollution themes) upon which port authorities may act. This table also shows the activity(ies) for which each pollution category is more significant, and the most impacted medium (air, water, or land).

2.2. Prevention and Mitigation Measures for Port Pollution

A significant number of technological and regulatory measures already exist for preventing and mitigating port pollution. This section reviews the existing measures and sets the stage for exploring current research in the various issues, which will be described in Section 4. Figure 2 summarizes the prevention and mitigation measures identified in the literature [2,8,12,16,17,18,19,21,29], showing which port pollution themes they impact. The boxes in gray indicate the different port pollution themes, with underwater noise being shown independently. The white boxes indicate measures that may be taken to decrease pollution in ports. Some of these measures may impact several different themes, for example, exhaust gas scrubbers clean the exhaust gases from sulfur oxides, thus decreasing air pollution in the port area (improved air quality), but some open-loop systems produce residues that may be dumped in the port waters. Insulation of ship’s equipment (machinery) decreases noise in the port area but also contributes to less noise being radiated underwater. Overall, it may be seen that a significant number of measures (21) are focused either on air quality management or on climate change management or both. This shows the importance of these two themes in port sustainability.

3. Materials, Sources, and General Approach

The literature review on technological and regulatory measures and academic research related with the topics indicated in Table 2 was carried out using the approach detailed below and recognizing that there are different sources for technological solutions, academic and practical studies, and regulatory measures.

Figure 3 shows the main organizations in the industry relevant for port pollution research and development: port authorities, terminal operators, equipment manufacturers, shipping companies, and classification societies. There are, in addition, a number of studies of interest developed by consultants and reports in the specialized press. Finally, a number of port associations are also relevant in this field: International Association of Ports and Harbors (IAPH), the American Association of Port Authorities (AAPA), the European Sea Ports Organisation (ESPO), and the World Association for Waterborne Transport Infrastructure (PIANC). Among these, the World Ports Sustainability Program of IAPH is especially important [30].

Terminal operators and manufacturers occasionally produce studies of some interest, for example, on the electrification of terminal equipment [31]. The International Maritime Organization (IMO) conventions, applicable to ships, such as the International Convention for the Prevention of Pollution from Ships (MARPOL) [32], deal with multiple forms of pollution and impact on ports. National governments are also obviously important as regulatory authorities (EPA, EMSA) emitting laws and guidance on various matters [33], but in the EU, most of the law concerning port pollution is actually a transposition of EU legislation. In recent years, classification societies have shown interest in the topic of port pollution as part of the broader topic of green shipping and energy transition. As might be expected, research, development, and innovation are also very active in both the industry and academia, with an immense corpus of literature in scientific journals and international conferences offering relevant insights into multiple aspects of green ports.

The selection criterion for industry-driven research, which may vary widely in quality, was to consider mainly studies from representative organizations of the port industry and main regulatory authorities (mentioned in previous paragraphs), major port authorities, classification societies, and only a few selected articles from reputed publications (detailing relevant manufacturer and shipping company contributions). Out of all these different stakeholders, Figure 3 shows, in bold, the categories with most relevance in promoting and carrying out research on the development of green ports through innovation, technical actions, or regulatory work. These were considered to be port associations and authorities, shipping companies, European Union legislation and local legislation, and academic research.

The first phase of the literature review consisted of screening the specialized press, the academic literature, and the websites of the main industry stakeholders to identify major port pollution themes and prevention and mitigation measures, of both technological and regulatory nature. The main results of this exercise are reported above in Section 2. The second phase consisted of searching with the aid of the Scopus database for the literature related with the keywords listed in

Table 3. List of keywords used in the bibliographic research.

Keywords	Keywords
Modal split	Alternative fuels
Intermodal and multimodal transport solutions	Green corridors
Synchromodality	Climate change adaptation
Gate appointment system	Noise management plan
Air pollution	Noise
Sulphur content in marine fuels	Underwater noise
Shore power cold ironing	Vibration
Railway connections	Light pollution
Last mile rail connections	Sewage
Dust in cargo handling	Oily waters
Greenhouse gases	Scrubbers
Ship speed restrictions	Residues of cargo
Just-in-time arrivals	Ballast water contamination
Electrification of trucks and cargo-handling equipment	Paints
Charging stations	Anti-fouling
Alternative fuels refueling points	Rainwater contamination with residues
Electrification of harbor crafts	Volatile organic compounds
Carbon capture and storage	Green fees
Generation of renewable energy	Environmental ship index

, generally accompanied by the word “port” or “terminal”. These keywords resulted from the previous screening of industry practices and regulatory developments reported in Section 2. The references dating from 2000 onwards were then restricted to subject areas “Engineering”, “Computer Science”, “Mathematics”, “Environmental Science”, Energy”, with document type “Articles” and language “English”. The resulting lists of references were then filtered in order to identify the most relevant ones, namely, those containing the most up-to-date approaches in the study of each type of pollution source or mitigation measure, as detailed below in Section 4.

The results of the search with the aid of the Scopus website for the literature are shown in Figure 4. The number of publications includes only major journal papers, conference papers, and book chapters. It may be seen that the five keywords that returned the largest number of publications were “air pollution”, shore power”, “alternative fuels”, “greenhouse gases”, and “electrification of equipment”. As can be seen, all keywords are related with emissions, be it of global-warming-related pollutants or pure air pollution. The next keyword was “ballast water contamination”, with substantial research undertaken on this difficult and disrupting factor for ecosystems. Finally, “climate change adaptation” and “intermodal and multimodal transport” have also attracted much research and, again, they are related to emissions. All the remaining categories showed much less research (less than 50 publications).

4. Technological and Regulatory Measures and Academic Research on Green Ports

4.1. Air Quality Management

One of the most important port pollution themes is the mitigation of air pollution, implying meeting appropriate levels, in the short and long term, of air quality by reducing the levels of SO_x, NO_x, and PM. These emissions are harmful for human health and for ecosystems, and arise not only from land-side transportation but also from ships and from cargo-handling equipment. In the EU, the National Emission Reduction Commitments Directive [34] requires Member States to report national emission inventories each year, including those of transport. A particularly concerning problem in some ports is air pollution arising from ever-larger cruise ships, ferries, and other passenger ships [35,36].

Regulatory requirements mentioned above entail the monitoring of air polluting emissions and adherence to reduction commitments on this matter. The reduction in emissions thus requires prevention and mitigation measures, for example, the EU limitation of the sulfur content of marine fuels used within ports and inland waterways [37]. This measure leads to higher fuel costs, and these may cause a decrease in the competitiveness of short-sea shipping, causing a modal shift back to road [38], thus undermining the competitiveness of ports.

Land-side transportation of cargo to/from the port is a significant contributor to air pollution [39]. Land-side transportation may use one or several different modes of transportation (road, rail, inland waterways), and port policies regarding this matter generally involve attempting to minimize emissions from vehicles (trucks, trains, and inland ships) as well as congestion, noise, wear of the infrastructures, and accidents. Also, when further developing ports and terminals, the impact of land-side transportation needs to be accounted for in all these respects. One common policy is focused on increasing the modal share of intermodal and multimodal transport solutions, resorting to modes presenting less impact, such as rail [40] and inland waterways [41]. This topic is often not listed within measures for mitigating pollution in ports, with notable exceptions being [42,43]. However, some research has been devoted to the promotion of more environmentally friendly transport systems [44]. In addition, some terminals operate under concession agreements that include explicit modal split targets [45].

In recent years, the concept of synchromodality has been proposed: making optimal use of all modes of transport and available capacity, at all times, as an integrated transport solution [46]. This concept has application for the entire logistic chain but also holds benefits for the port as it could contribute to decreased congestion in the road network in and around the port area and decreased air pollution and GHG emissions. Synchromodality involves a mode-free booking of transportation services, with dynamic (real time) planning and routing (decision making), thus requiring information availability and visibility, something that is only achievable through the digitalization of logistic chains and with the cooperation of stakeholders [47].

Road transportation within the port area leads to congestion, accidents, and emissions, leading some terminals, especially container terminals, to develop and implement gate appointment systems [48,49]. These allow trucking companies to book time slots for picking up or delivering containers, avoiding excessive queues in the accesses to terminals. This has become a practical necessity due to the large capacity of container ships now deployed in some routes, which lead to significant peaks in gate congestion that can only be smoothed down using gate appointment systems.

The provision of shore-power infrastructure (cold-ironing) is another measure with positive impact in reducing air pollution. The electrification of cargo-handling equipment, of trucks and of trains coming to terminals, is also beneficial in terms of air pollutant emissions. These measures will be further detailed in Section 4.2. Quite frequently, port authorities, railway network managers, and operators engage in infrastructure projects aiming at connecting the port with the national railway network (last mile connection or more substantial connections) or merely promote the electrification of the railway access to the port in order to avoid using diesel locomotives [50].

Air pollution also includes a significant number of particles released as dust, primarily in dry bulk cargo-handling operations. This is harmful for the air quality in the port area, and in windy conditions, other areas surrounding the port may also be impacted [22,51]. Port terminals are adopting a number of mitigation measures such as more efficient cargo-handling systems, surrounding the infrastructure with fences (walls or trees), or using enclosed conveyor belts. It is also possible to use water sprays [52], chemical suppressants, dust extraction systems, limit the drop heights, and perform cargo handling only in favorable weather conditions, to try to limit the spreading of dust when handling or storing dry bulk cargos in open stockyards. Continuous air quality monitoring enables the assessment of dust levels and the effectiveness of mitigation measures, with port authorities having now installed, in some cases, air and water quality sensors for monitoring air quality [53].

4.2. Climate Change Management

Ports are nowadays also under significant pressure to reduce the main greenhouse gases (GHG) emissions: CO₂, CH₄, and N₂O. These gases arise from the entire scope of port users and equipment, including ships, terminal equipment, and land-side vehicles, as well as from industries located within the area of jurisdiction of ports. A number of established methodologies exist for emission inventories [54,55,56], allowing general conclusions on shipping emissions to be made, as reported in [57]. These models can also be used to evaluate the impact of different emissions-cutting policies, such as electrification in the ports of Seattle, New York, and New Jersey [58]. The studies of [59,60] present an accurate general methodology applicable to ships at sea that could also be applied to port areas.

With regard to measures to limit GHG emissions, some ports, like Los Angeles and Long Beach, in the USA, have introduced sea areas adjacent to the port where ship speed is restricted or offer incentives for speed restrictions [61]. However, this practice may lead to unwanted side effects, as more black carbon may be released as a result of speed reduction [62,63]. Some authors have studied the combination of optimized ship scheduling and speed reduction [64] or have studied the effects of speed reduction in ports in specific regions [65]. A few research projects have studied the concept of just-in-time arrivals in order to limit the number of ships queuing (and producing emissions due to the need to produce electrical power) and to limit the emissions of ships while sailing in the port approaches. This concept depends on a strong cooperation between different stakeholders and on sophisticated information technology (IT) systems, possibly using artificial intelligence for advanced prediction of ship arrivals. In order to facilitate this, the voyage charter contract of BIMCO has also been updated with a new clause [66]. The importance of just-in-time arrivals has been recognized by IMO in its portal Greenvoyage 2050 [67,68]. Another possibility for reducing emissions is to reduce the turnaround time for a ship at berth, allowing the vessel to reduce speed at sea and still carry out the same amount of transport work on an annual basis, while also reducing emissions in port [69,70].

Once at berth, shore power has a role to play in the reduction in emissions, provided that such infrastructure is offered in the port and ships are equipped to utilize it. Shore-power installations are capital-intensive as they require significant upgrades to the port and grid infrastructure, including new high-voltage power cables and transformer stations. These investments imply public–private partnerships with national energy grid companies (either owners or operators of the grid) and require careful feasibility studies [71]. Due to the substantial investments required, government grants often play a crucial role. However, as concluded in [72,73], both in Europe and the US, millions could be saved in health costs if shore power was in widespread use. As of 2017, only 28 ports across the world could provide shore power, while in 2024, about 90 ports are already capable of doing so [74]. The challenges in the development of the necessary infrastructure are reported in [75]. The investment in shore power may be more justified for terminals receiving cruise ships and ferries, as these ships generate significant amounts of electrical power while at quay. In the EU, Regulation 2023/1804 presents the targets for shore-side electricity supply in maritime ports [76]. Facilitation of the implementation of shore power in ports is provided by relevant guidelines developed by EMSA [77]. In the United States, the California Air Resources Board (CARB) issued an at-berth regulation [78], requiring container ships, reefers, and cruise vessels to connect to shore power (or employ another approved emission-control strategy).

Another ongoing trend for reducing GHG emissions in port is the adoption of alternative fuels, batteries, or fuel cells for port and terminal cargo-handling equipment, with [31] providing examples of currently available equipment and their manufacturers. In fact, many manufacturers focus on the electrification of external trucks and cargo-handling equipment such as quay gantry cranes, yard gantry cranes, and terminal trucks [79]. In particular, terminal trucks have been substituted in some large container terminals by electric automated guided vehicles (AGVs) [80]. With regard to cargo-handling equipment, electric versions are now available for most equipment, retrofit solutions to hybrid or fully electric are also possible, and regenerative brake systems are available. Smaller cargo-handling equipment is also available, using LPG or fuel cells for propulsion. A number of studies have been devoted to the assessment of the sustainability benefits of these novel solutions [81,82,83]. Electrification places an extra burden on the local electrical grid, which needs to be designed in such a way to accommodate the variability of load requirements [8].

In the case of external trucks, these are generally the property of private companies (road haulers), and any increase in the utilization of electric or alternative fuel trucks involves the cooperation between the port authority, port terminal operators, and these companies. Financial incentives may be required to assist in the adoption of these greener trucks, and charging stations and refueling points need to be provided by the port authority or terminal operators. In any case, it must be taken into consideration that trucks traveling for long distances with large loads are still not eligible for using batteries, as the technology is still not mature. Recognizing this but still attempting to limit emissions, some ports only allow modern trucks in port facilities, while providing funding, infrastructure, and training [61,84].

Another concern of port authorities is harbor craft emissions (pilot boats, ferries, tugs, etc.), for which electrification is a feasible option. The installation of hybrid power systems is the most common form of vessel electrification. Another common and cost-effective measure is to upgrade older propulsion engines to the newest EPA and EU emission standards [8]. However, it should be noted that emissions from harbor crafts typically constitute a very small percentage of port emissions and are frequently owned and operated by private companies, meaning that cooperation with these partners is essential for emission mitigation.

Some port authorities have also begun examining carbon capture and utilization (CCU) and carbon capture and storage (CCS) as instruments that could help in reducing CO₂ emissions. In fact, carbon dioxide could be used as a coolant, or to produce sustainable methanol or biofuels. The port of Antwerp [85] and North Sea Ports [86,87] have both conducted studies on this matter. Further studies have been devoted to the offloading in ports of CO₂ captured onboard ships [88].

In order to counterbalance the emissions occurring in ports due to ships, trucks, trains, barges, cargo-handling equipment, and industries, many port authorities have developed or promoted projects aiming at generating renewable energy within the port area and promoting the principles of circular economy [89]. This is being carried out using solar panels, wind turbines, or cogeneration plants. ABS and AAPA [8] report that most ports use or plan to use solar panels. Solar panels are the port’s preferred local energy source, as building rooftops and canopies over parking spaces can provide suitable space for solar power generation. The wider variety of energy sources leads to the need to improve the power system design. In this respect, automation and energy efficiency technologies may provide significant gains in dynamic power management.

Another possibility for reducing air pollution and greenhouse gases emissions is to provide in-port alternative fuels for ships (nonconventional fuels not yet currently in full production and utilization in marine applications, including liquefied natural gas (LNG), liquefied petroleum gas (LPG), methanol, ammonia, hydrogen, biofuels, and synthetic fuels) and the associated bunkering infrastructure and equipment [90]. These fuels have different applicability to different ship types and sizes [91] and present various pros and cons [92]. Shipping companies remain, thus, highly uncertain about the optimal course to take with regard to future fuels for their new buildings [51], and this has implications for the development of port infrastructure, equipment, and procedures for bunkering alternative fuels [93,94]. In most ports across the world, these alternative fuels are not available or are available in limited quantities, and this makes shipping companies reluctant to adopt these fuels [95,96,97,98]. Numerous port authorities are currently developing efforts to attract to industrial areas in their ports producers of these alternative fuels, which will use renewable energy produced in the port itself; see the case of green hydrogen in [99,100]. Most production processes are, indeed, highly energy-intensive, so the availability of abundant renewable energy is essential.

In some cases, ports are grouping together to set up green corridors, as originally proposed at the UN Climate Change Conference [101]. These are zero-emission (or at least low-emission) routes between ports (specific maritime routes or multiple ports across two regions) enabled by the existing, or potential availability of, alternative fuel and bunkering infrastructure. The requirements and challenges, including the contribution of ports, is discussed in [102]. These corridors are meant to foster the confidence of shipping companies [103,104]. A study of EU green corridors is provided in [105], while [92,106] show the drivers, challenges, and pathways to integrate ports in green shipping corridors. Academia has also cooperated with port authorities to study specific green corridors [107].

It is, however, becoming clear that some degree of climate change will inevitably occur, and port infrastructures will be impacted [108] by the rising sea level, changes to wave conditions, increased severity and likelihood of storms and cyclones, increased storm surges, more intense precipitation, and river flooding or droughts. One study [109] indicates that 86% of ports around the world are exposed to more than three climate-related and geophysical hazards, and climate risks are estimated to be around USD 7.6 billion per year. There is already a substantial body of literature on this topic, including updates on climate change forecasts and its impact on coastlines and reviews of international policies to address such impacts [110,111]. Some authors [112] account for uncertainty inherent to climate change in the port adaptation policies, while others discuss the relative merits of climate change mitigation versus adaptation measures [113]. A risk assessment and cost effectiveness analysis of different port adaptation measures is presented in [114], while the reinforcement of breakwaters, crown-wall crest elevations, slope construction, equipment refurbishment, or relocation of berths are studied in [115].

4.3. Noise, Vibration, Light, and Odor Pollution

The operation of port terminals leads to significant noise and some vibration in the port and surrounding areas [22], affecting populations and buildings, implying that managing noise from ships, port equipment, and land-side transport vehicles is critical. The issue of noise in ports was reviewed in [116] and studied for residential areas around ports in [117], while in [118], an update on noise in ports was provided. It has become a common practice in some ports to monitor ambient noise, often as a result of requirements included in the Port Noise Management Plan, which also prescribes measures for mitigating excessive noise. In the EU, the Environmental Noise Directive 2002/49/EC (END) [119] has significant implications for port authorities. NoMEPorts published a practice guide on port area noise mapping that assists in complying with the directive [120]. In addition, the European Commission has issued general purpose noise assessment methods for infrastructures [121], and ISO developed a standard covering the measurement of airborne noise emitted by vessels on inland waterways and harbors [122]. Some research projects have proposed networks of sensors for continuous monitoring of noise and vibration levels across the port area [123].

Noise pollution originates from ships (diesel engines, ventilators, pumps, compressors, and reefer containers) and may be partially contained through the use of silencers in exhaust pipes, insulation in fan rooms, and resilient mountings. The provision of shore power to ships is also an efficient way to reduce noise in ports. Yard gantries and terminal trucks are also known to contribute to noise in port terminals. In [124], it is mentioned that in the port of Koper terminals, sound-emitting devices, such as warning alarms, were replaced by devices with less impact. In addition, it is also possible to perform cargo handling only during the daytime, insulate the diesel engines, use electric equipment, use softer ground pavements, check tire pressure, and close the terminal for land-side operations during night time. The impact of noise in ports was made even clearer during the pandemic, as traffic was greatly reduced [125]. Finally, the production of renewable energy using wind turbines in the port area could also lead to additional noise.

Another aspect related to noise that has come into evidence very recently is the waterborne (underwater) noise radiating from ship navigation within the port area. This might be harmful for fish, and especially for mammals, in ports that are located near natural reserves or other protected areas [126,127]. A review of this theme is provided in [128], while in [129], the utilization of bubble curtains to mitigate the noise of dredging is examined. A rare underwater noise monitoring survey in a port is reported in [130], while a similar survey studied the impact of noise on dolphins [131].

Floodlights and blinking vehicle lights in a night environment have significant impact, often named “light pollution”, especially if the port or terminal is located within an urban area. Light produced by ships is considered less important, except perhaps light coming from cruise ships. The impact of light at night may be reduced through the use of LED lights and motion sensors [18]. Using motion sensors in low-traffic areas can significantly reduce energy consumption, and LED lights afford a saving of up to 75% energy. Finally, pollution is also considered to include various odors from handling and transformation of perishable bulk solids, waste handling and treatment, fish handling, and from water purifiers [132,133].

4.4. Ship- and Cargo-Related Pollution

Water pollutants are also a problem in ports, including sewage (black or gray water), oily waters, residues from exhaust gases scrubbing (gypsum, acidic residues), or waters containing cargo residues. Some port authorities have installed a network of sensors for monitoring water (also air and sediment) quality with regard to pollutants like oil and chemicals [134]. Most of these types of pollution are regulated internationally by IMO [32], their discharge is prohibited (especially sewage and oily water), and ports are required to provide access to land-based equipment and infrastructure to collect, treat, and dispose of such residues (additional service to ships by external private companies). Some ports across the world have also banned the operation of exhaust gases scrubbers of the open-loop type in order to prevent the release of contaminated residues into the water [135]. Ships also produce solid residues such as garbage and old materials that need to be collected by trucks for further appropriate treatment, otherwise there is the risk of simply moving residues between locations. In the European Union, port reception facilities for ship-generated waste and cargo residues are required [136,137,138]. In some cases, pollution may be caused as a result of accidents involving spills of liquid substances; therefore, port authorities need to have a spill response plan for dealing with such situations and invest in high-quality containment booms, absorbent materials, and training of suitable spill response teams.

Additional forms of water pollution are the discharge of non-treated ballast water from ships, as this water may bring non-native micro-organisms, fauna, and flora, which then harm and deregulate local ecosystems [139]. Ballast water pollution has been regulated by IMO in [140] and for biofouling in [141]. Its applicability has been recently expanded to recreational craft less than 24 m [142,143]. In some cases, ship hull paints detach slowly from the ship’s surfaces (mainly underwater but also above the waterline), and some of these contain substances that are harmful for the environment and ecosystems. These paints have been used to reduce the growth of biological material on underwater surfaces of vessels, and their use is regulated by IMO [144]. Port State Control (PSC) plays a crucial role in ensuring compliance with IMO regulations on these topics.

During the handling of cargo and its storage, especially dry bulks, the contamination of rain water with residues of dry or liquid bulk cargos needs to be managed. This is generally carried out by providing containment and treatment means such as dams and canals to collect the contaminated waters and lead them to tanks for further treatment [145]. Also, industries and logistic facilities located in the port area may also produce residues that, if not properly contained and stored, may lead to soil contamination with solids and liquid noxious substances. Finally, some ports collect and reuse rainwater for non-potable purposes like cleaning and maintenance, reducing the consumption of treated fresh water.

Finally, the release of volatile organic compounds (VOCs) from cargo tanks and port tanks into the atmosphere, especially those tanks containing crude oil or refined products from oil, is also a significant issue [146]. VOCs may be methane and non-methane (NMVOC), contributing to the greenhouse effect, and affecting the ozone, human health, and food production. Some VOC emissions may be toxic and carcinogenic [147]. Some technical systems are used to capture these emissions. In some ports or terminals, it is required that tankers utilize a vapor emission control system (VECS). In such case, both the shipboard and shore arrangements are to operate in accordance with [148,149]. In recent years, these systems, in widespread use across several industries, have seen significant developments in monitoring (digitalization), control, enhanced filtration, and methane capture [150,151].

4.5. Management Approaches to Pollution Prevention and Mitigation

Considering the wide range of possible measures for the prevention and mitigation of port pollution, port authorities have felt the need for a system of sustainable management indicators, proposing a set of multidimensional indicators [132]. A more recent review of sustainability indicators [133] suggests 10 indicators for sustainability, linked to 8 social indicators and 11 economic indicators. Structural equations are used for modeling ports [152], allowing the conclusion that collaboration between stakeholders in the port community and with customers and suppliers is essential in improving port sustainability performances [153]. The way these indicators are then reported by port authorities is discussed in [153,154,155]. AAPA has published an environmental management handbook to enable port authorities to comprehensively protect and improve environmental conditions in and around their facilities [156].

In addition to all the measures and policies described above, many port authorities concede discounts on port tariffs for ships that present especially low emissions [157]. This award was first introduced in 1994 for oil tankers, chemical tankers, LNG and LPG tankers, and container ships and was extended in 2011 to inland vessels. It is based on the Environmental Ship Index (ESI), which is directly related to GHG and air polluting emissions and the use of shore power [33]. It provides, as a benefit, discounts on port tariffs of 5–15%, and the impact of these green port dues is discussed in [44,158,159]. While the above scheme is applicable to ships, terminals also now have incentives, in some cases, to become greener. This is promoted by port authorities through the utilization of green terminal concessions [160,161]. These concession agreements include clauses mandating the utilization of environmental management systems, limits on emissions (with incentives and penalties), electrification of equipment targets, modal split targets, and responsibility allocation for remediation measures [15]. Port authorities have engaged in a number of green port certification schemes, as proposed by industry associations or government bodies dealing with environmental management and sustainability, for example, the EcoPorts initiative of ESPO [162] and the Green Marine program of ports in North America [163]. Finally, many ports and terminals can now apply for a certification of environmental management systems in accordance with ISO 14001 [164].

5. Summary and Discussion

The above section described the state of the art with regard to numerous port pollution prevention and mitigation measures.

Table 4. Emerging and established pollution prevention and mitigation measures (X identifies a measure as emerging or established).

Pollution Prevention and Mitigation Measures	Emerging	Established	Pollution Prevention and Mitigation Measures	Emerging	Established
Synchromodality	X		Carbon capture and storage	X
Electrified rail connections		X	Generation of renewable energy	X
Intermodal transport		X	Dust management		X
Gate appointment system		X	Odor management		X
Speed limits for trucks, trains		X	Exhaust gas scrubbers		X
Green fees		X	Treatment of rainwater		X
Low-sulfur marine fuels		X	Garbage and solids collection		X
Shore power	X		Sewage collection		X
Alternative fuels	X		Oily waters collection		X
Reduce time in ports		X	Collection of VOC		X
Ship speed restrictions		X	Non-harmful paints		X
Just-in-time arrivals	X		Ballast water contamination		X
Electrification of trucks, handling equip.		X	LED lighting and motion sensors	X
Electrification of harbor crafts	X		Insulation of handling equipment		X
Charging and refuel stations	X		Insulation of ship equipment		X

summarizes which of the measures are emerging and which are already established in the industry. It may be concluded that a total of nine measures are still emerging, implying that about one-third of the total number of measures is still in its infancy. It is noteworthy that many of these involve heavy investments and/or extensive cooperation between different stakeholders. The remaining are already established and are used on a day-to-day basis in ports worldwide.

It is also useful to summarize all measures with regard to the stakeholders responsible or with some degree of intervention in their implementation, as shown in

Table 5. Stakeholders with relevant roles in the pollution prevention and mitigation measures (X indicates that the stakeholder is involved; ● indicates that the stakeholder is expected to incur significant capital expenditures for the relevant measure; numbers in column 2 indicate the magnitude of total capital expenditure on a scale up to 7).

Pollution Prevention and Mitigation Measures	Port Authority			Terminal Operator	National Government	Service Providers	Bunker, Fuel Suppliers	Equipment and Materials Manufacturer	Electrical Network Manager	Shipping Company	Charterer	Shipper	Forwarders 3PL	Shipping Agency	Trucking Company	Railway Operator	Barge Operator	Total Stakeholders:
Synchromodality			5	X						X ●		X	X ●	X	X	X	X	8
Electrified rail connections	X	●	5		X ●				X ●							X		4
Intermodal transport	X	●	6	X	X ●					X		X	X	X	X	X ●	X ●	10
Gate appointment system			2	X ●				X					X	X	X			5
Speed limits for trucks, trains	X	●	1	X	X								X		X	X		6
Green fees	X	●	1	X						X							X	4
Low-sulfur marine fuels	X		3				X ●	X		X				X			X	6
Shore power	X	●	6	X ●	X ●			X	X	X ●							X ●	7
Alternative fuels	X	●	7		X		X ●			X ●				X	X	X	X	8
Reduce time in ports	X		2	X						X			X	X			X	6
Ship speed restrictions	X		1		X					X	X	X		X			X	7
Just-in-time arrival			2	X						X	X	X	X	X			X	7
Electrif. of trucks, handling equip.			4	X ●				X	X						X			4
Electrif. of harbor crafts	X	●	4			X ●		X	X ●								X ●	5
Charging and refuel stations	X	●	5	X ●	X ●		X	X	X						X			7
Carbon capture and storage	X		7	X		X ●		X		X ●								5
Generation of renewable energy	X	●	6	X	X ●			X	X ●									5
Dust management			3	X ●						X		X					X	4
Odor management			3	X ●						X		X					X	4
Exhaust gas scrubbers	X		5					X		X ●								3
Treatment of rainwater			3	X ●				X										2
Garbage and solids collection	X		2			X ●				X				X			X	5
Sewage collection	X		2			X ●				X				X			X	5
Oily waters collection	X		2			X ●				X				X			X	5
Collection of VOC	X		2	X ●		X ●				X				X			X	6
Non-harmful paints			2		X			X		X ●							X	4
Ballast water contamination			4			X		X		X ●								4
LED lighting and motion sensors	X	●	3	X ●				X	X	X								5
Insulation of handling equipment	X		2	X ●				X								X		4
Insulation of ship equipment	X		2					X		X ●							X ●	4
Total measures involved:	21			18	9	7	3	15	7	21	2	6	6	12	7	6	18

with a cross (X). It is important to mention that the table was drawn with a landlord port authority in mind. It is assumed that the port authority enforces regulations issued by the national government and regional organizations (EU, for example) and that the port is fitted with rail and inland navigation accesses in addition to road accesses. A number of companies engaged in logistic activities are included, as some measures also have implications for transport chains. It is assumed that shipping companies are the owners and operators of ships, while the charterer is a voyage charterer (little control over the ship).

Table 5 shows that most measures are of a collaborative nature, as identified in the literature review, with stakeholders acting in various roles: enforcers, promoters, users, and suppliers. The number of stakeholders varies from ten (intermodal transport) to two (treatment of rainwater). Synchromodality requires the intervention of at least eight stakeholders, showing that any activity involving different modes of transportation requires significant cooperation. This explains why ports often find intermodal operations difficult to promote. However, they represent an efficient path to green port operations and foster the expansion of the port hinterland [165,166]. Measures relating to more efficient port operations (just-in-time arrival, leading to less emissions) are also strongly collaborative (seven stakeholders), with the same applying to measures related to the provision of low-sulfur fuel, alternative fuels, shore power, and charging stations. On the contrary, measures related to the collection of residues generally require the involvement of fewer stakeholders (typically four or five).

In the analysis carried out per stakeholder, port authorities, shipping companies, and barge operators are the most important stakeholders in greening ports (involved in 19 to 21 measures), followed by terminal operators, national governments, equipment and materials suppliers, and shipping agents. This ranking implies that port and national authorities play an essential role as regulatory bodies and enforcers of maritime laws, but all need the support of technology providers (equipment manufacturers). Cargo- and logistics-related stakeholders are also involved but are less important. It can be seen that 20 out of 30 measures relate to air pollution and greenhouse gas emissions, while 7 measures relate to cargo and ship residues, and 3 relate to noise, vibration, and light pollution.

Table 5 also shows the stakeholders (●) that are expected to bear the main capital expenditures associated with each port pollution measure, as per conclusions taken from the literature review. These capital expenditures cover investments in infrastructures, superstructures, equipment, and software. Again, the port authority and terminal operators are expected to frequently incur expenses (ten), followed by shipping companies (shipowners or operators) with eight measures. National governments (five), service providers (six), and barge operators (four) form a second group of stakeholders that are expected to have to invest in greening measures. The remaining ones are not expected to incur significant capital expenditures to implement these measures, although they may be involved in many other ways.

Still based on the literature review, the first column in Table 5 shows a classification of the magnitude of the investments required to implement each measure, in a Likert scale of 1 to 7, corresponding to an increasing cost magnitude. The provision of alternative fuels and carbon capture and storage has the highest capital costs, as both depend on substantial facilities for their production or processing, utilization, and storage. The production of renewable energy in ports and the supply of shore power are also expected to lead to significant costs, as wind turbines, large areas of solar panels, and power cables and transformer stations are typically expensive. Providing the port with an extensive network of intermodal connections (rail and inland waterways, including trains and barges) is also a significant undertaking. The electrification of tracks, provision of charging and refueling stations throughout the port, and software for synchromodality are expected to require less investment. Most other measures are considered less expensive, with regulatory speed restrictions for ships and trucks and green fees being the most effective, cost-wise.

It is also interesting to analyze in detail the emerging measures regarding capital intensity and number of stakeholders.

Table 6. Emerging measures classified with regard to capital intensity and number of stakeholders involved.

Pollution Prevention and Mitigation Measures	Capital Intensity	Stakeholders Involved
Synchromodality	5	8
Shore power	6	7
Alternative fuels	7	8
Just-in-time arrivals	2	7
Electrification of harbor crafts	4	5
Charging and refuel stations	5	7
Carbon capture and storage	7	5
Generation of renewable energy	6	5
LED lighting and motion sensors	3	5
Average	5	6

shows that the average intensity is 5 out of a scale of 7. The supply of alternative fuels and the implementation of carbon capture are considered especially capital intensive (7), and require the cooperation of eight and five stakeholders, respectively. These characteristics explain the related significant costs and implementation issues. Shore power and production of renewable energy also involve significant investments in the electrical distribution grid and in power generation equipment. A significant number of stakeholders needs to be engaged, adding to the difficulty in implementation. On the opposite extreme, just-in-time arrivals require a relatively low capital investment, but still involve a high degree of cooperation. Overall, it is important to note that there is no emerging measure with both low investment and low number of stakeholders.

With regard to a more strategic perspective, it is clear that emissions will dominate research and industry concerns for many years. Technologies involved in producing and bunkering alternative fuels, improving batteries, and increasing the production of renewable energy still need considerable research, especially as decreasing costs across supply chains is critical to making them more affordable. As regulators worldwide are adopting ambitious market-based measures that have the potential to financially impact shipping operations, the port and shipping industry needs to identify sources of financing to support the huge investments needed and engage the support of national and regional block authorities. Relevant stakeholders need to cooperate closely to identify crucial ports where investments are most needed and ensure the necessary funding, possibly following the approach taken by the port of Singapore [167]. Another topic related with climate change that requires further research deals with optimum sets of measures to deal effectively with challenges such as severe storms, sea rise, and droughts, leading to more resilient ports. All of these need to consider that ports often base their business on the handling of fossil fuels, and sustainability, in practice, largely conflicts with their customer base.

6. Conclusions

This paper reviewed the literature on measures for prevention and mitigation of port pollution, focusing mainly on port operations. This review indicated that the literature on this topic is very substantial, with many significant contributions both from academia and port industry, allowing the identification of 30 significant measures (adopted or in study) to prevent and mitigate port pollution.

Academic and industry research is very focused on emissions, be them of global-warming-related pollutants or air pollution, especially emission inventories. The topics of shore power, alternative fuels, and equipment electrification have also received a lot of attention. However, ports still struggle to provide alternative fuels to ships in sufficient quantity, as this requires substantial infrastructure investments, with only a small number of ports being ready at this stage. The most recent proposal is to use carbon capture to cut CO₂ emissions from ships and from industries in port areas, but this poses significant technical and economic challenges and requires further research. Climate change adaptation of ports is also critical, considering the current slow pace of the mitigation of GHG emissions. Cargo and ship residues collection is more straightforward, and not much of the literature is dedicated to these aspects or to port-generated noise. In general, the literature review revealed that ports and regulatory bodies are heavily involved in studying, legislating, and even researching within the scope of port sustainability.

The relation between digitalization and sustainability has highlighted that IT systems are deeply involved in just-in-time arrival management, intermodality and synchromodality. Also, a growing tendency is for ports to invest in networks of sensors for monitoring real-time air and water quality, noise and vibration in the port area, providing information to digital twin models and enabling future use of artificial intelligence applications in port operations. However, this connection between sustainability and digitalization has been largely left out of the scope of this paper, but it is an aspect well deserving of a dedicated review and further research.

Another topic for further research is the quantification and comparison of economic investments in sustainability and their associated return. Sustainability investments are often difficult to evaluate, especially in the case of emerging technologies, and also because carbon emission prices, fuel prices, and “guaranteed” rates for energy are, in practice, highly volatile. Moreover, many benefits are not necessarily financial, and their monetization is difficult and contentious. This aspect certainly warrants more detailed analysis as it is critical for greening ports.

In addition, the real effectiveness of green certification schemes for ships could also be further studied. The same applies to regulatory and technical practices for port pollution prevention and mitigation across different jurisdictions, regions, countries, and maritime hubs, supporting a more detailed knowledge of worldwide variations in these policies, taking into account different local environmental, economic, social, and cultural conditions.

This paper provides useful policy insights as it shows that most measures for port pollution prevention and mitigation depend on a strong collaborative effort of up to ten stakeholders. Port authorities clearly have a driving seat in this process, being involved in most of the proposed measures, in many cases as regulators. However, port authorities need to recognize that it is not sufficient to develop legislation at a local or national level, as it is also necessary to engage stakeholders and assess whether the technology is in place to fulfil often overly ambitious greening objectives. Finally, gathering all relevant stakeholders is especially important, as implementing policies for promoting greener ports often requires significant capital expenditures that are only possible through a concerted effort. Port authority policies should, thus, focus on attracting the necessary funding to attain the ambitious sustainability goals adopted at the national or international level, which are, indeed, an urgent necessity in contemporary societies.