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

Category: Urban Air Quality

Volume: 17 | Issue: 6 | Pages: 1527-1538
DOI: 10.4209/aaqr.2017.03.0120
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Ying-Yi Chen1, Chung-Yen Lu2,3, Pei-Chun Chen4,5, I-Fang Mao6,7, Mei-Lien Chen 1

  • 1 Institute of Environmental and Occupational Health Sciences, School of Medicine, National Yang Ming University, Taipei 11221, Taiwan
  • 2 Department of Sport and Health Management, Da-Yeh University, Changhua 51591, Taiwan
  • 3 Department of Chinese Medicine, Taipei Hospital, Ministry of Health and Welfare, New Taipei City 24213, Taiwan
  • 4 Department of Public Health, China Medical University, Taichung 40402, Taiwan
  • 5 Department of Medical Research, China Medical University Hospital, Taichung 40447, Taiwan
  • 6 Department of Occupational Safety and Health, Chung Shan Medical University, Taichung 40201, Taiwan
  • 7 Department of Medical Research, Chung Shan Medical University Hospital, Taichung 40201, Taiwan


Suspended particulate concentration was higher in MRT station than in the atmosphere.
PM concentration decreased from tunnels to platforms to entrances in MRT station.
PM metal composition exceeded 30% of total PM mass; Fe had the highest concentration.
This is the first study to assess PM concentration changes after tunnel washing.
Tunnel washing reduced PM concentration in the MRT station after 2–3.5 months.


The 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.


Particulate matter Metro Subway Indoor air Fine aerosol

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