Fig. 1: Overview of the methodology applied in this study.

The data of this study were collected at four underground subway stations in Shanghai for AM, noon, and PM periods during weekdays and weekends for four seasons, followed by data pre-processing and model selection. We selected Random Forest with SHAP value for influencing factor analysis, applied the model to all the subway stations in the whole city, and analyzed the association between the PM concentration, exposure, and the point-of-interest distribution.