Particulate matter concentrations, physical characteristics and elemental composition in the Milan underground transport system

► PM10 levels in subway stations were studied and its elemental composition determined. ► OPC's were used to determine size distributions. ► PM10 concentrations were greater than in ambient air by up to a factor of 8. ► Source contributions were estimated on the platform and mezzanine levels. ► PM10 levels were largely due to local sources such as brake, wheel and cable wear.