## 2 Data and Model Experiment
### WRF-Chem Model Setup
#### 2.3.3 Cases Setup  
(1) Evaluation of overall air quality in 2020  
The month of October was used as a proxy of the entire year of 2015 since the pollutant concentrations in October 2015 were very similar to those in the whole year (details are shown in Section 3.1). WRF-Chem simulations were conducted with the emissions in four 2020 scenarios and the emissions in 2015. The simulated concentrations of PM\({}_{2.5}\), PM\({}_{10}\), SO\({}_{2}\), NO\({}_{2}\), CO, and O\({}_{3}\) were compared between results of the four 2020 scenarios and the result of 2015, in order to evaluate the effectiveness of the 13 th FYP policy on air quality. The meteorological conditions for 2020 scenarios were assumed to be the same as the meteorological conditions in 2015. The results are shown in Section 3.3.  
(2) Evaluation of air quality during pollution episodes  
To identify the air quality status, we analysed the annual air quality situation and air pollution events based on the data observed in four urban stations (Baogang, Chisha, Shayuan, and Haizhuhu) in Guangzhou Haizhu district (Figure 1). A pollution episode was defined as a short period consisting of subsequent days (at least one day) with the AQI \(\geq\) 101 [62]. A heavy pollution episode was a pollution episode with AQI \(\geq\) 201 [62].  
The pollution episodes in 2015 are shown in Table 2 (more information is shown in Table S3). The table shows that the number and the pollution level of pollution episodes had seasonal characters. The pollution episodes occurred more often in winter, and heavy pollution was observed in the summer and winter. The Shayuan station and Haizhuhu station suffered pollution episodes more than other stations in 2015, and Shayuan was the only station where the heavy pollution episodes were observed in both winter and summer (14-28 January 2015, and 3-8 August 2015, respectively). The two heavy pollution episodes were typical pollution (PM\({}_{2.5}\) and NO\({}_{2}\) pollution in winter, O\({}_{3}\) pollution in summer [63]). Therefore, the two heavy pollution episodes in Shayuan were analysed with pollution and meteorology progress (results shown in Section 3.1.2). Also, the meteorology conditions of these two episodes were applied in the 2020 scenarios numerical simulations with WRF-Chem to evaluate the effectiveness of the 13 th FYP policy on air quality of pollution episodes (specifically, PM\({}_{2.5}\) and NO\({}_{2}\) pollution for the winter episode, O\({}_{3}\) pollution for the summer episode). The simulation results are shown in Section 3.4.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Station** & **Season** & **Event Frequency (Units)** & **key Pollutant** & **Max Pollution Level** \\ \hline Baogang & Spring & 5 & PM\({}_{2.5}\), NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\  & Summer & 4 & O\({}_{3}\) & **Heavy pollution** \\  & Autumn & 3 & PM\({}_{2.5}\), NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\  & Winter & 9 & PM\({}_{2.5}\), NO\({}_{2}\) & Moderate pollution \\ Chisha & Spring & 4 & PM\({}_{2.5}\), NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\  & Summer & 4 & O\({}_{3}\) & **Heavy pollution** \\  & Autumn & 3 & NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\  & Winter & 7 & PM\({}_{2.5}\), NO\({}_{2}\) & Moderate pollution \\ Shayuan & Spring & 7 & PM\({}_{2.5}\), O\({}_{3}\) & Moderate pollution \\  & Summer & 5 & O\({}_{3}\) & **Heavy pollution** \\  & Autumn & 12 & PM\({}_{2.5}\), NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\  & Winter & 7 & PM\({}_{2.5}\), NO\({}_{2}\) & **Heavy pollution** \\ Haizhuhu & Spring & 6 & PM\({}_{2.5}\), NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\  & Summer & 3 & O\({}_{3}\) & Light pollution \\  & Autumn & 10 & NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\  & Winter & 12 & PM\({}_{2.5}\), NO\({}_{2}\), O\({}_{3}\) & Moderate pollution \\ \hline \hline \end{tabular}
\end{table}
Table 2: Pollution episodes observed at Haizhu monitoring stations in 2015.