Analysis of Aerosol Composition and Assessment of Tunnel Washing Performance within a Mass Rapid Transit System in Taiwan

Chung-Yen Lu,I-Fang Mao,Mei-Lien Chen,Pei-Chun Chen,Ying-Yi Chen

doi:10.4209/aaqr.2017.03.0120

Abstract

ABSTRACTThe metro system is the main mode of transportation in Taipei City. The air quality of metro stations is crucial for passengers. This study investigated particle size distribution and its elemental composition and assessed tunnel washing performance in the Taipei Rapid Transit System (TRTS). A 24-hour particle sampling process was performed in the tunnels, platforms, and entrances and exits to measure particulate matter (PM)2.5 and PM10 concentrations in an underground metro station and to analyze PM metal components. PM10 and PM2.5 concentrations decreased sequentially from the tunnels to the platforms and then to the entrances and exits to ambient environment in the metro station. The main metal components of suspended particulates in the TRTS mainly included iron, barium, copper, manganese, magnesium, aluminum, chromium, zinc, nickel, and lead. The total PM10 and PM2.5 metal proportions were 33.9%–24.7% and 32.9%–22.8%, respectively. Furthermore, the effectiveness of tunnel washing in reducing the PM concentration was investigated. Monitoring results showed an increase in PM10 and PM2.5 concentrations after tunnel washing on the first day. The PM concentration started to decrease from the second day. Furthermore, 3.5 months after tunnel washing, the PM10 concentration decreased by 45.9%, and 2 months after tunnel washing, the PM2.5 concentration decreased by 71.3%. The mechanism of the continuous reduction in the PM10 concentration after cleaning is probably related to the porous material of tunnel walls, which may provide a deposition sink for aerosol particles, as well as the filter effect of the air conditioning system. This is the first study to use full-section tunnel washing to reduce PM exposure at mass rapid transit (MRT) stations. Although full-section tunnel washing reduced the PM concentration in the metro station, accessorial technology, such as the air conditioning system or platform design, may help in reducing the exposure of MRT passengers.

Highlights

Mass rapid transit (MRT) systems are the main modes of transportation in metropolitan regions
24-hour sampling of PM10 and PM2.5 was performed in the tunnel, platform, and ground-level entrances and exits in Station A, and the samples collected on the filter paper were analyzed through inductively coupled plasma-mass spectrometry (ICP-MS); the corresponding results are shown in Tables 2 and 3 as well as in Figs. 1 and 2
The results of the PM10 analysis revealed that the total PM10 concentrations in the tunnels, platforms, and ground-level entrances and exits were 423.00, 227.00, and 86.00 μg m–3, respectively, with metals accounting for 33.9%, 24.6%, and 24.7% of the particulate content in these respective areas

Summary

Introduction

Mass rapid transit (MRT) systems are the main modes of transportation in metropolitan regions. A PM concentration higher than that in surrounding environments has been reported in underground metro stations or stations of other MRT modes in metropolitan regions such as Helsinki (Aarnio et al, 2005), London (Seaton et al, 2005), Rome (Ripanucci et al, 2006), Beijing (Li et al, 2006), Budapest (Salma et al, 2007), Prague (Braniš, 2006), Seoul (Kim et al, 2008), Buenos Aires (Murruni et al, 2009), Paris (Raut et al, 2009), Sydney (Knibbs and de Dear, 2010), New York (Wang and Gao, 2011), Los Angeles (Kam et al, 2011), Mexico City (Mugica-Álvarez et al, 2012), Barcelona (Querol et al, 2012), and Milan (Colombi et al, 2013). PM collected from MRT underground stations have been reported to exhibit a higher metal content than that collected from surrounding environments, with its metal components mainly including iron (Fe, the primary metal component), manganese (Mn), chromium (Cr), copper (Cu), barium (Ba), zinc (Zn), and nickel (Ni) (Aarnio et al, 2005; Murruni et al, 2009; Nieuwenhuijsen et al, 2007; Salma et al, 2009; Querol et al, 2012; Martins et al, 2016)

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Conclusion