Particulate matter concentrations in a high-quality rubber-tyred metro system: the case study of Turin in Italy

Particulate matter concentrations measured in railway metro systems are consistently higher than at street level (up to an indoor/outdoor ratio equal to 10), with dangerous effects for passenger health. These concentrations are mainly produced both by the mechanical friction and wear processes at the rail-wheel-brake interfaces and by the re-suspension caused by the turbulence generated by the train transit. The literature abounds in case studies dealing with the elevated concentrations and the analysis of the atomic composition of particulate matter as well as the epidemiological studies regarding the effects on human health. By contrast, the problem of reducing particulate matter concentrations was not much discussed. Starting from these considerations, the aim of this research was to investigate the PM concentrations of a ‘‘high-quality’’ metro system equipped with useful devices for reducing these concentrations: rubber-tyred, platform screen doors, an advanced ventilation system and a variable slope of the longitudinal profile. A measurement campaign was performed in the metro of Turin (Italy). Experimental results show that the indoor concentrations are statistically lower than those measured in outdoors; that particulate matter levels are closely correlated to the train frequency; the particulate matter concentrations measured inside trains are lower than the ones measured at station platform. From these results, it is possible to note that particulate matter concentrations measured in a ‘‘high-quality’’ metro system are significantly lower than the ones measured in ‘‘traditional’’ railways. This result is significant and poses the bases for the definition of useful interventions for retrofitting metro systems.