The contribution of ambient sources to particulate pollution in spaces and trains of the Prague underground transport system

During a fixed-route including (i) surface walk on streets, (ii) underground spaces (corridors, vestibules and platforms) and (iii) underground trains of the Prague Metro Rail System (PMRS) a fast response portable photometer was used to measure concentrations of PM10 (particulate matter <10 μm). On the basis of more than 100 monitored trips the PMRS may be characterised as more polluted than the streets above. On average, the highest PM10 concentration was recorded inside the Metro trains (113.7 and 1.44), the second highest in the underground spaces of stations (102.7 and 1.29), followed by outdoor environment (74.3 and 0.85), expressed in μg m−3 and in dimensionless relative normalised units, respectively. In spite of the statistically significant difference (p<0.001) between ambient and underground PM10 levels recorded by the photometer, the ambient concentrations were tightly associated with those from the underground spaces (r2=0.820) as well as from the Metro trains (r2=0.774). The correlation between concentrations from both underground microenvironments was even higher (r2=0.964) indicating a common source of aerosol inside the PMRS. Since also reasonable correlation was found between fixed site monitors (FSM) and both ambient and underground photometer PM10 levels a strong influence of surface traffic-related particulate pollution on the underground air quality is suggested.