Variations of the PM2.5 and PM1.0 concentrations inside the train over time
Fig. 7 By recording the door opening period, we found that it mostly lasts around 20 s, but sometimes lasted longer than 50 s. The variations of PM concentrations inside the subway train between the times when the door opened and closed can be seen in Fig. 7. The shaded areas correspond to the train’s door opening periods. The PM concentrations inside the train increased greatly during the door opening period, as the dirty air on the platforms flowed into the car. The PM concentrations then decreased after the subway car’s doors closed.