Investigation into Beijing commuters’ exposure to ultrafine particles in four transportation modes: bus, car, bicycle and subway

Abstract

Traffic-related air pollution contributes considerably to commuters' daily air pollution exposure. Ultrafine particles (UFP) is one of the most commonly measured traffic-related air pollutant during commuting. There are very limited studies on commuting exposure to air pollution in China. To fill the knowledge gap, we conducted the first study that compares commuters' UFP exposure among four modes in a Chinese city. In this study, we measured particle number concentration (PNC) levels of 63 trips in four transportation modes: bus, car, bicycle and subway in 2015 on a typical commuting route between urban and suburban areas in Beijing. We found that buses experienced the highest PNC (geometric mean (SD): 35,066 (10,856) particles cm−3), followed by bicycles (geometric mean (SD): 28,277 (7942) particles cm−3), then cars (geometric mean (SD): 16,302 (5156) particles cm−3), and finally the subway (geometric mean (SD): 13,245 (2936) particles cm−3). Within the subway mode, we detected the highest PNC at station entrances, followed by the transfer tunnel, while cabin areas showed the lowest levels. For the cabin areas of the subway mode, PNC concentrations were higher when the trains were overground than underground. Measures are needed to reduce commuters’ exposures, particularly those traveling by bus and bicycle. Switching the bus transportation system from diesel to cleaner power, such as compressed natural gas or electricity, may help.