# Environmental Impact of the Natural Gas Liquefaction Process: An Example from China
## 2 Method
### Life Cycle Impact Assessment
#### 2.3.1 Calculation of the Environmental Impact Potential  
The product's environmental impact potential is the sum of all the environmental emission impacts in the entire product system, and the formula is expressed as follows  
\[EP(j)=\sum EP(j)_{i}=\sum\left[Q_{i}\ \times\ EF(j)_{i}\right] \tag{1}\]  
where \(EP(j)\) is the contribution of the product system to the \(j\)th potential environmental impact, \(EP(j)_{i}\) is the contribution of the \(i\)th emission substance to the \(j\)th potential environmental impact, \(Q_{i}\) is the emission of the \(i\)th substance, and \(EF(j)_{i}\) is the equivalent factor for the \(j\)th potential environmental impact of the \(i\)th emission substance. The determination of the equivalent factor varies with different types of environmental impacts. Typically, the relative impact size of other substances is calculated with reference to a standard substance.  
According to the established inventory and taking the actual conditions of China's environment into account, as well as combining them with the pollutant emissions during the natural gas liquefaction production process (the pollutants mainly included CH\({}_{4}\), dust, CO\({}_{2}\), CO, SO\({}_{2}\), NH\({}_{4}\)\({}^{+}\), and H\({}_{2}\)S), the environmental impact was divided into five categories: global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), photochemical ozone creation potential (POCP), and dust potentials (DP) [21]. In addition, the environmental impact potential of each type of pollutant was calculated separately. Among them, the gases that had an impact on the GWP mainly included CO\({}_{2}\), CO, and CH\({}_{4}\). Taking CO\({}_{2}\) as a reference substance, the equivalent factors were 1, 2, and 25, respectively. The gases that had an effect on the AP mainly included SO\({}_{2}\), NH\({}_{4}\)\({}^{+}\), and H\({}_{2}\)S. Taking SO\({}_{2}\) as a reference substance, their equivalent factors were 1, 1.88, and 1.88, respectively. The gas that affected the EP was NH\({}_{4}\)\({}^{+}\), and, taking NO\({}_{3}\)\({}^{-}\) as the reference substance, its equivalent factor was 3.64. The gases that affected the POCP mainly included CO, CH\({}_{4}\), and SO\({}_{2}\). Taking C\({}_{2}\)H\({}_{4}\) as a reference substance, their equivalent factors were 0.03, 0.007, and 0.05, respectively. The substance that had an effect on the DU was mainly dust, so its reference substance was dust itself, and its equivalent factor was 1.  
Based on Table 2, the impact potential of LNG production in the Shanxi Province was calculated and is shown in Table 4. Similarly, we calculated the impact potential of the other seven provinces, as shown in Table 5.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type of EI** & **Pollutants** & **Reference Materials** & **Equivalency Factor** & **Output of Pollutant** & **Impact Potential of Pollutant (kg)** & **Impact Potential of EI (kg)** \\ \hline \multirow{3}{*}{**GWP**} & CO\({}_{2}\) & \multirow{3}{*}{CO\({}_{2}\)} & 1 & 79.1496 & 79.1496 & \multirow{3}{*}{562.8499} \\  & CO & & 2 & 6.5007 & 6.5007 & \\ \cline{1-1}  & CH\({}_{4}\) & & 25 & 18.8280 & 18.8280 & \\ \hline \multirow{3}{*}{**AP**} & SO\({}_{2}\) & \multirow{3}{*}{SO\({}_{2}\)} & 1 & 0.0023 & 0.0023 & \multirow{3}{*}{0.0436} \\  & NH\({}_{4}\)\({}^{*}\) & & 1.88 & 0.0213 & 0.0213 & \\ \cline{1-1}  & H\({}_{2}\)S & & 1.88 & 0.0007 & 0.0007 & \\ \hline \multirow{3}{*}{**EP**} & NH\({}_{4}\)\({}^{*}\) & NO\({}_{3}\)\({}^{-}\) & 3.64 & 0.0213 & 0.0213 & \\ \cline{1-1}  & CO & & 0.03 & 6.5007 & 6.5007 & \\ \cline{1-1}  & CH\({}_{4}\) & C\({}_{2}\)H\({}_{4}\) & 0.007 & 18.8280 & 18.8280 & \\ \cline{1-1}  & SO\({}_{2}\) & & 0.05 & 0.0023 & 0.0023 & \\ \hline \multirow{3}{*}{**DU**} & dust & dust & 1 & 0.0019 & 0.0019 & 0.0019 \\ \cline{1-1}  & & & & & & \\ \hline \end{tabular}
\end{table}
Table 4: Impact potential of liquefied natural gas production in the Shanxi Province (per unit).