## 2 Emission Sources at Seaports  
Seaports are regarded as transport hubs that link seaborne transport by vessels to inland transport by trucks, trains, and barges. Cargo and passengers are loaded onto and discharged from vessels at seaports with the destinations and origins at inland locations. Many seaports have been developed as logistic hubs, where different companies are co-located to perform various logistics activities and value-added services including transportation, warehousing, sorting, processing, and distribution of goods for national and international trade. For example, according to a survey study by the property consultancy Knight Frank (www.maritimegateway.com, accessed on 24 September 2023), which assessed 41 UK ports using 13 factors, the Port of Liverpool is the top port-centric logistics hub in the UK. Further, some ports have been developing as energy hubs in the transition of decarbonisation by producing, transporting, importing/exporting, storing, converting, distributing, and trading alternative fuels and energy. According to IMO [10], port emission sources are classified into two types: stationary-type sources and mobile-type sources. This classification is mainly based on the emission  
Figure 1: Methodological framework. source's functionality and relationship to the cargo. Stationary sources include offices, warehouses, storage yards, quayside facilities, gate facilities, rail terminal facilities, buildings, parking spaces, manufacturing plants, industry plants, power plants, electrical grids, electric charging facilities, lighting, maintenance facilities, heating ventilation and air conditioning (HVAC) systems, etc. These stationary sources are not directly related to cargo movements, but may be associated with or support cargo or person mobility. Mobile sources include seagoing vessels, support vessels (e.g., tugs, push-boats, tenders, fire-boats, pilot boats, police boats), cargo handling equipment, heavy-duty vehicles, light-duty vehicles, locomotives, etc. Table 1 summarises the seaport emission sources from the functionality perspective. Focusing on mobile-type emission sources, the Port Authority of New York and New Jersey has published several annual air emission inventories from the emission source categories including cargo handling equipment, heavy-duty trucks, rail locomotives, ocean-going vessels, and harbour craft (tugs, tow boats, and push-boats). Table 2 gives the GHG emissions by different source categories in tonnes/year at the Port of New York and New Jersey in 2006 and in 2021, where CO\({}_{2}\)e represents carbon dioxide equivalents [11]. The percentages indicate the emission shares by each category in that year. It can be observed that heavy-duty trucks and ocean-going vessels were the top two emission categories and had similar shares of emissions in 2006, but the category of heavy-duty trucks was significantly higher than other categories in 2021, which accounted for 49% of the total emissions. Nevertheless, the categories of ocean-going vessels and cargo handling equipment were also significant, with more than 20% share of the total GHG emissions each for both years. The implication is that the estimation of the emission inventories from different categories could shed light on the prioritisation of emission source categories for decarbonisation. Another classification of emission sources is based on the reporting organisation's responsibility. The GHG Protocol set up the internationally accepted GHG accounting and reporting standards for business [12]. According to a company's organisational boundary regarding the operations under its control, GHG emissions are classified into three scopes. Scope 1 refers to the direct emissions generated onsite by the reporting company from owned or controlled sources, e.g., emissions from combustion in owned or controlled equipment, vehicles, boilers, furnaces, and production processes.