Passengers’ Exposure to PM2.5, PM10, and CO2 in Typical Underground Subway Platforms in Shanghai

Based on the statistics of Shanghai metro corporation, currently, above 7 million commuters travel on the Shanghai metro system each day. However, information related to the characteristics of indoor air particulate matter (PM) level in underground stations of this system is limited. The concentrations of PM2.5, PM10, and CO2 were measured in this study with portable monitors at two typical underground subway platforms of Shanghai Metro Line 9 during 19 January to 22 January. Experimental results showed that: (1) The anthropogenic activity had a significant impact on the contaminant concentration. Pronounced diurnal variations were observed in the underground subway platforms, and the concentrations of PM2.5, PM10, and CO2 displayed a bimodal pattern, with peaks between 7:00 and 10:00 and between 16:00 and 19:00 during the rush hour of workdays. Meanwhile, the PM2.5/PM10 ratio indicated that the human activities contribute the most course particles. (2) The pollutant density had a slightly reduction just a few seconds before the subway train came. It could be explained by the dilution of piston effect on the subway station through tunnel and passageway. (3) The contaminant samples of different station layer were also collected during off-peak hours with the same stable passengers. Correlation between pollutant concentration and station depth has been confirmed.