## 2 Materials and Methods
### System Boundary  
The sources of GHG emissions in this study are shown in Table 2. The main sources can be summarized as follows: (1) emissions generated by MSW transportation vehicles, including the transportation from collection point to transfer station, the transportation from transfer station to waste disposal plant (landfill site, incineration plant, or composting plant) or recycling center, and the transportation of incineration and composting residues to landfill site; (2) emissions from decomposition of MSW in landfill; (3) emissions from incineration of MSW and emission reduction benefits of GHG brought by electricity generation from incineration; (4) emissions from composting of MSW; and (5) emission reduction benefits of energy consumption saved by recycling of renewable resources. Due to the lack of data, GHG emissions from energy consumption for daily operation of transfer stations and disposal point facilities are not discussed in this paper. In addition, most of the landfill gas in China is emitted into the air without recycling, so the energy recycling of landfill site is also not discussed in this paper.  
The GHG emissions from disposal of MSW primarily include CO\({}_{2}\), CH\({}_{4}\), and N\({}_{2}\)O. In the transportation process, CO\({}_{2}\), CH\({}_{4}\), and N\({}_{2}\)O were considered as the GHGs emitted by vehicle exhaust. In the landfill process, only CH\({}_{4}\) emissions were taken into account. Furthermore, CO\({}_{2}\) was considered to be generated by the decomposition of biological carbon, so it was not included in the calculation. In the composting process, CH\({}_{4}\) and N\({}_{2}\)O emissions were taken into account, without considering CO\({}_{2}\). In the incineration process, only CO\({}_{2}\) emissions were taken into account, as CH\({}_{4}\) and N\({}_{2}\)O were assumed to be negligible.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Waste Management Activities**} & \multirow{2}{*}{**Including or Not**} & \multirow{2}{*}{
\begin{tabular}{c} **Including or Not** \\ \end{tabular} } \\ \cline{1-1}  & & & & & \\ \hline Collection and transportation & & & & \\ Fixed facility operation & & & & \\ Landfill & & & & \\ Energy recover from landfill & & & & \\ Composting & & & & \\ Incineration & & & & \\ Energy recover from incineration & & & \\ Recycling of renewable resources & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: GHG emissions evaluation scope in the paper.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Waste Components**} & **Waste Composition (\%)**[51] & **Moisture Content (\%)**[52] & **Total Carbon** & **Fraction of Possil** & **Fraction of** & **Heat Value** \\  & **Composition (\%)**[51] & **Content** (\%)**[52] & **Content on Dry Basis (\%)**[53] & **Carbon Content** (\%)**[41] & **Degradable** & **on Dry** \\  & & & & & \\ Kitchen waste & 47.85 & 82.1 & 50.6 & 0 & 15 & 4650 \\ Ash and brick & 3.48 & 11.5 & 0 & 100 & 0 & 6980 \\ Wood & 3.33 & 21.6 & 53.03 & 0 & 43 & 18,610 \\ Paper & 20.83 & 29.2 & 46.13 & 1 & 4 & 16,600 \\ Textile & 2.34 & 22.9 & 61.03 & 20 & 24 & 17,450 \\ Plastics & 20.74 & 32.5 & 78.77 & 100 & 0 & 23,260 \\ Glass & 1.23 & 2.4 & 0 & 0 & 0 & 140 \\ Metal & 0.2 & 5.4 & 0 & 0 & 0 & 700 \\ \hline \hline \end{tabular}
\end{table}
Table 1: MSW characteristics in Beijing.