In this study, the concentrations and physicochemical features of PM10 and PM2.5 collected within underground facilities of one of Mexico City’s subway stations were compared with those of the ambient air PM. The mass pattern concentrations related to workdays and weekends as well as the diurnal period are similar outside the station and in the platform. During the night when the trains frequency is smaller and
eventually is null, the mass concentration of PM10 decreases within the underground