*2.1. Research Area*

The air pollutant monitoring stations in the Beijing area mainly detect the concentration of various air pollutant gases (such as carbon monoxide, sulfur dioxide, and ozone) and PM1 and PM2.5. These monitoring stations are distributed in various districts of Beijing, as shown in Figure 1. The data and monitoring records collected by the monitoring points will be published in real-time for easy access and research.

**Figure 1.** Distribution map of monitoring stations in Beijing.

There are also some objective reasons for selecting the Beijing area for study. The Beijing area is one of the more effective observation points of NASA's meteorological satellites, and it is also the network point of the ground aerosol automatic observation network (AREONET). Therefore, different data can be used for comparison. Moreover, Beijing is the capital of China, with a relatively high population density and frequent haze. Therefore, the significance and feasibility of the research are high.
