## 2 Data Sources and Study Area
### Study Area  
Our study focuses on the urban area of Nanning, Guangxi Zhuang Autonomous Region, China. As the capital of Guangxi Zhuang Autonomous Region, Nanning is not only the economic, political and cultural center of the region, but also a city in a rapid development stage [72]. It has a superior geographical location, located in the central and southern part of Guangxi, bordering many cities, and has rich natural resources and a unique geographical environment [73]. Nanning is an ideal region for evaluating the applicability of our research approach due to its unique climate conditions and PM\({}_{2.5}\) pollution sources. In terms of climate, Nanning has a typical humid subtropical monsoon climate with distinct four seasons, abundant precipitation, and high air humidity. In this climate context, high atmospheric water vapor content provides favorable conditions for the complex chemical reactions of chemical components in PM\({}_{2.5}\), which in turn leads to dynamic changes in its concentration and chemical composition. Precipitation, as a natural mechanism of atmospheric purification, has a complex impact on PM\({}_{2.5}\) concentrations. In the early stage of precipitation, PM\({}_{2.5}\) is prone to accumulation due to high atmospheric stability. However, after precipitation, as atmospheric conditions change, PM\({}_{2.5}\) concentrations may rise again [74]. In addition, high air humidity can cause PM\({}_{2.5}\) particles to absorb moisture and grow, changing their \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dataset** & **Time Range** & **Spatial Resolution** & \
\begin{tabular}{c} **Temporal** \\ **Resolution** \\ \end{tabular} & **Usage Part** \\ \hline \multirow{3}{*}{
\begin{tabular}{c} ChinaHighAirPollutants \\ (CHAP) \\ \end{tabular} } & \multirow{3}{*}{2000–2023} & \multirow{3}{*}{1 km} & Day & not used \\ \cline{3-3} \cline{5-5}  & & & Month & Jan 2012–Dec 2023 \\ \cline{3-3} \cline{5-5}  & & & Year & 2012–2023 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Data Sources. optical and physical properties, which significantly affects their transmission and diffusion processes in the atmosphere. Studies have shown that when relative humidity increases, the water-soluble components in PM\({}_{2.5}\) will absorb water vapor, causing the particle size to increase and the particles to develop the ability to scatter and absorb light, thereby affecting atmospheric visibility [75]. In terms of PM\({}_{2.5}\) pollution sources, along with the accelerated urbanization process, the urban economy of Nanning urban area has developed rapidly. According to the statistics in 2024, the permanent population of Nanning urban area has reached 8.9408 million, and the number of urban motor vehicles has exceeded 3.37 million. The continuous increase in urban population and the continuous expansion of traffic scale have made the PM\({}_{2.5}\) pollution sources present obvious diversified characteristics. Emissions from industrial production activities are one of the important sources of PM\({}_{2.5}\). Various factories will release a large amount of waste gas containing PM\({}_{2.5}\) and other pollutants into the atmosphere during the production process. Exhaust emissions in the transportation sector should not be ignored either. The continuous increase in the number of urban motor vehicles has led to a significant increase in exhaust emissions. In addition, dust generated during urban construction and fumes emitted by the catering service industry have also played an important role in the formation of PM\({}_{2.5}\). PM\({}_{2.5}\) from different sources has obvious differences in chemical composition, particle size distribution, etc. This difference further increases the complexity and difficulty of PM\({}_{2.5}\) pollution. Nanning urban area has a total area of approximately 8000 square kilometers, and its jurisdiction covers several administrative districts, such as Xingning District, Qingxiu District, Jiangnan District, Xixiangtang District, and Yongning District [76].