Fig. 6: Platform PM2.5 and the passenger exposure estimated in the Shanghai subway network.

The figures illustrate PM2.5 concentrations estimated during the a morning, b noon, and c evening episodes on weekdays, respectively, and passenger PM2.5 exposure level during the d morning, e noon, and f evening, respectively. The exposure levels to PM were categorized into five percentile-based categories for visualization (20%, 40%, 60%, 80%, and 100%).