Indoor and outdoor measurement of airborne particulates on a commuter train running partly in tunnels

Wear processes from mechanical braking, rail/wheel contact, the railway electrification system and re-suspended materials due to the turbulence of passing trains in tunnels and stations have been suggested to be the main contributors to particulate matter levels inside trains. In this study, onboard monitoring was performed on a commuter train stopping at underground and aboveground stations. The concentration and size distribution of particulates were monitored for both indoor and outdoor levels. The results show that the levels of PM10 and PM2.5 inside the train were about one-fifth of the outdoor levels. Significant increases in indoor particulate number concentrations were observed in tunnel environments and there was a slight increase when the doors were open. Differences in the size distributions of micro- and nano-sized particulates could be identified for different tunnels