Abstract
ABSTRACT Air quality inside metro systems is a critical issue for commuters and metro employees because of the considerable time they spend traveling or working in such systems. This study measured the PM10, PM2.5, particle number (PN), and CO2 levels and particle mass size distributions inside operating trains to reveal the factors influencing the concentrations and size distributions of particulate matter (PM) inside metro train carriages traveling in different environments. The measurement results demonstrated that the CO2 level was associated with ridership and that the PM levels and particle mass size distributions were highly affected by the immediate surroundings of the train, such as whether it was journeying through underground tunnels or on ground-level tracks as well as its direction of travel. Furthermore, the particle mass size distributions inside the metro train carriages exhibited a clear triple-mode pattern, whereas those for the ground-level and underground routes differed considerably due to different particle sources.
Highlights
Metro systems constitute a major public transportation mode and typically serve billions of commuters annually in metropolitan areas worldwide because of their advantages, such as environmental friendliness, efficiency, low emission, and high capacity, as compared with other transportation modes
The measurement results demonstrated that the CO2 level was associated with ridership and that the particulate matter (PM) levels and particle mass size distributions were highly affected by the immediate surroundings of the train, such as whether it was journeying through underground tunnels or on ground-level tracks as well as its direction of travel
Despite the different metro routes, these findings suggest that the PM10 and PM2.5 levels inside metro train carriages were remarkably affected by the surrounding conditions of the trains, such as their journey in underground tunnels or on ground-level tracks
Summary
Metro systems constitute a major public transportation mode and typically serve billions of commuters annually in metropolitan areas worldwide because of their advantages, such as environmental friendliness, efficiency, low emission, and high capacity, as compared with other transportation modes. PM in a metro system strongly affects health (Karlsson et al, 2006; Bachoual et al, 2007; Karlsson et al, 2008; Steenhof et al, 2011) According to these previous studies, the widely varying PM concentrations on metro platforms and inside train carriages in different metro systems depend on a complex interplay of factors such as differences in the length and design of stations and tunnels, system age, wheel and railtrack materials and braking mechanisms, train speed and frequency, passenger densities, ventilation and air conditioning systems, and cleaning frequency (Salma et al, 2007; Moreno et al, 2014; Woo et al, 2018). The primary element in metro PM is Fe, and other elements are Si, Mn, Cr, Cu, Ca, and K (Querol et al, 2012; Cusack et al, 2015; Moreno et al, 2015; Chen et al, 2017)
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