# Port-Related Shipping Gas Emissions--A Systematic Review of Research
###### Abstract
This method is characterised as activity-based and data-demanding, since it requires a higher level of input parameters for each movement activity (MA); however, it is able to produce near instantaneous emission estimation on a vessel-by-vessel basis at high resolution (in time and space) [12; 13]. In a bottom-up approach, emission estimations are obtained for each movement type by combining engine energy output (EO) or FC with EF and time (T) values that correspond to specific activities (e.g., hoteling, manoeuvring and navigation) [15; 16]. To figure out the total shipping emissions in a certain area and time period, all estimated quantities of each activity are combined and scaled up over all trips [12]. In the bottom-up approach, both energy-based (EB) and FB methods can be applied. These methods are shown in the EB Equations (2) and (3), along with the FB Equation (4) [12; 16]. When gas quantification is conducted by relying on an EB approach, EO is determined by multiplying total engine power (P) by the actual percentage of engine work output, expressed as load factor (LF). In this case, EF is defined as the mass of pollutants emitted per an engine's energy output:  
\[\text{E}=\text{EO}\times\text{EF}\times\text{T} \tag{2}\]  
\[\text{EO}=\text{P}\times\text{LF} \tag{3}\]  
\[\text{E}=\text{FC}\times\text{LF}\times\text{EF}\times\text{T} \tag{4}\]Since the bottom-up approach is data-excessive, it is generally applied in small-scale ship emissions inventories in regional and port contexts, and to aggregate the required data the Automatic Identification System (AIS) is often used. AIS transmits near real-time dynamic information about vessel speed, course and position, which is crucial for anticipation of ship-based emissions. Therefore, high-resolution ship motion data from AIS could be a source of reliable relative ship operation profiles, such as travel time and average speed between waypoints at sea in short time intervals, and could be used to identify ship routes [12]. Although the installation of AIS is required by the International Maritime Organisation (IMO) on commercial ships with 300 gross tonnage (GT) and all passenger ships, relying solely on information from this device, a proportion of marine traffic remains invisible [17]. To improve data quality, more than one source of traffic information should be considered in gas emission inventory development. However, regardless of data quality, the method by which it is used is of equal importance. That is why, in this paper, a multi-layered analysis approach is applied with the aim of finding the most applicable methodology for the estimation of gas emissions from ships in port areas. The methodology, as the end result of this research, should provide an empirically structured basis for the further development of novel ship-sourced gas emissions indexing models in port areas. To ensure the adequate standard of the whole review process, Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines were followed in this paper [18]. Regarding the search strategy method employed, a bottom-up systematic review of the literature that explored port-related shipping emissions was conducted by applying relevant keyword and reference thread analyses in the Web of Science Core Collection, Scopus and Google Scholar databases. Search and screening of the selected papers was carried out by the authors.