# Port-Related Shipping Gas Emissions--A Systematic Review of Research
## 3 Discussion and Results  
### Analytical Overview of the Literature--First Layer  
By conducting a systematic review of the literature according to PRISMA 2020 guidelines, 32 original papers that explored shipping emissions in 80 ports between 2008 and 2021 were selected for further analysis. With the aim of providing a transparent overview of the literature, Table 1 lists the abbreviations of the aforementioned studies and papers, while their reference numbers are listed at the end of the paper. The analytical overview of records was conducted by examining, comparing and linking applied methods and databases with studies and papers, which were the original reference sources, as summarised in Table 2.  
The analytical overview process allowed for the following conclusions to be drawn. Primarily, it was found that the authors of all papers relied on bottom-up methodologies, since they explored port-related emissions with good data coverage. An additional top-down approach was applied only for two records in order to make an output value comparison. Therefore, the EB method was predominant since it was used in 26 papers. By contrast, the FB approach was applied for only three publications, and for the same number of papers a combination of both methods was used. Datasets applied for calculating emissions were obtained both locally and from studies. Locally sourced datasets that were derived from Local Port Authorities (LPAs), Local Port Communities (LPCs), National Maritime Organisations (NMOs), AIS, Vessel Traffic Services (VTSs), traffic density data (TDD) or from studies offered information about marine traffic through TD on the ships and their MA. LF and EF data, as more complex components in the gas emissions determination process that depends on specific information about vessels and their activity, were either taken from studies as predefined default values or were estimated on a methodological basis from the same sources. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Abbreviation** & **Reference Number** & **Abbreviation** & **Reference Number** & **Abbreviation** & **Reference Number** \\ \hline CAPSS/PAQman\(\copyright\) & [20] & CARB 06 & [21] & CARB 07 & [22] \\ FEMA 09 & [23] & EEA 09 & [24] & EEA 13 & [25] \\ EEA 16 & [26] & EEA 19 & [16] & EEM 10 & [27] \\ ENTEC 02 & [28] & ENTEC 05 & [29] & ENTEC 07 & [30] \\ ENTEC 10 & [31] & IMO GHG 09 & [32] & IMO GHG 14 & [33] \\ SMED 04 & [34] & IVL 05 & [35] & L R 95 & [36] \\ MAN & [37] & MEET 98 & [38] & NEI 10 & [39] \\ POLA 04 & [40] & POLA 08 & [41] & POLA 09 & [42] \\ POLA 12 & [43] & POLA 13 & [44] & POLB 10 & [45] \\ SEA & [13] & STEAM & [46] & US EPA 06 & [47] \\ US EPA 09 & [48] & PIRAEUS 09 & [49] & SAMSUN 10-15 & [50] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Abbreviations of cited studies and papers with their reference numbers. The data on the amount and type of emissions in all examined papers were analysed but were not comparable even for the same ports. This was due to several factors. First, the different papers used different methods and datasets for the emission calculations, so comparing the gas volume values would not describe the relationship between the measurements in a relevant way. Even if the same method was applied in the same