Commuter exposure to particulate matter and particle-bound PAHs in three transportation modes in Beijing, China
Introduction
Human exposure to fine particulate matter (PM2.5) and ultrafine particles (UFPs) has been associated with increases in mortality and morbidity worldwide (Haberzettl et al., 2012, Sioutas et al., 2005). It was suggested that a 10 μg m−3 increase in two-day mean PM2.5 was associated with 1.5% increase in total daily mortality (Schwartz et al., 1996). To protect the population from chronic and acute exposure, guideline levels for PM2.5 were set to 10 μg m−3 (annual) and 25 μg m−3 (24-h) by the World Health Organization (WHO, 2006).
Due to rapid economic and population growth, major megacities of China are now facing much greater transportation demand, resulting in increased vehicular emissions as well as air pollution burden. It has been reported that the annual mean mass concentration of PM2.5 in most Chinese cities were above 100 μg m−3 (Yang et al., 2011). Residents in Chinese megacities are now frequently exposed to high ambient concentrations of PM2.5 (Zhao et al., 2009, Zhou et al., 2012), which are much higher than the WHO recommended guideline values and the national ambient air quality standards (NAAQS) for PM2.5 in China (with annual arithmetic mean of 35 μg m−3).
Beijing, a megacity with more than 20.69 million residents, has the most extensive and complex traffic system in China. Compared with megacities of other countries, the road traffic situation in Beijing is unique in that streets are filled by a chaotic mix of pedestrians, cars, trucks, buses, bicycles, and other motorized and non-motorized small vehicles. Moreover, vehicle population in Beijing increased significantly during the past 20 years, with a rapid annual growth rate of 13% (Wu et al., 2011) and reached as high as 5.35 million to date. This rapid growth rate in the number of vehicles contributes to increased vehicular emissions in Beijing. There is an urgent need to assess personal exposure to multiple particulate pollutants in traffic related environments in Beijing.
A previous study of Chinese crowd behavior patterns showed that urban residents' average outdoor activity time in Beijing is 3.5 h day−1, and Beijing adult residents spend average 87 min day−1 in traffic. In addition, it also pointed out that about 140 million Chinese residents lived within 50 m from roads (MEP PRC, 2013). Therefore, urban residents spend considerable amount of time in traffic-related environment each day. Several studies indicated that commuters' exposure to different pollutants was greatly dependent on the choice of commuting (Chan et al., 1999, Chan et al., 2002a, Chan et al., 2002b, Kam et al., 2011a, Kam et al., 2011b). Although a few personal exposure studies related to traffic commuting were conducted in recent years (Du et al., 2011, Du et al., 2012, Huang et al., 2012, Li et al., 2006, Li et al., 2007, Li et al., 2008), they either focused on a certain mode of transportation or on average mass concentrations of gaseous pollutants or inhalable particulate matter (PM). Very few studies have reported information of other important PM pollution parameters (e.g., particulate number concentration, PNC) or its chemical characteristics (e.g., toxic chemical species such as PAHs) which are critical to assess potential health risk.
In this study, personal exposure concentrations of particulate pollutants including fine and ultrafine particles, particle-bound PAHs in three major transportation modes (subway, bus, and walking) in Beijing were investigated with the following objectives: (1) to determine PNC, PM2.5 mass concentrations (PMC) and particulate PAH concentrations in different transportation modes in Beijing; (2) to assess time dependent personal exposure concentrations of PM in roadway transportation modes (bus and walking); and (3) to evaluate potential health impact from personal exposure to particulate PAHs. To our best knowledge, it is the first time to investigate multiple particulate pollutants (including chemical composition) in different transportation modes in Beijing.
Section snippets
Sampling sites
Sampling was carried out between December 10 and 23, 2011 near Peking University (N 39°59′21.13″, E 116°18′25.10″). It is near Zhongguancun, also named as the “the silicon valley” of China. This area is densely-populated (residents, office people and pedestrians) and associated with high flow of vehicles on busy streets. Three commonly used commuting modes (i.e., walking, riding buses, and taking subway) were selected for this study. The walking route (red line in (in the web version) Fig. 1)
Concentrations of measured pollutants in different traffic environment
Ambient temperature and RH ranged from −6.6 °C to 12.8 °C (averaged 2.6 °C) and 13%–74% (averaged 27%) during the campaign. Prevailing wind direction was from southwest, with an average speed of 1.5 m s−1. In this study, PNC, expressed as number of fine (including ultrafine) particles per cubic meter air, and PMC both varied widely in different transportation modes. Real time monitored PNC ranged from 0.1 × 104 to 4.1 × 104 (median value: 1.1 × 104) cm−3 when commuted by walking, 0.03 × 104 to
Conclusions
Concentrations of PNC, PMC and PAHs in three primary public transportation modes (walking, bus, and subway) were investigated and compared in Beijing. Walking pedestrians and bus commuters were exposed to a much broader range of PNC and PM2.5 mass concentration. Chinese characteristic roadside sources (e.g. outdoor barbecuing and cigarette smoking) contributed to high PM concentrations in roadway transportation environments. Dust might contribute not only to PM concentrations in roadway
Acknowledgments
The authors would like to acknowledge Xiaosen Xie, Fengwen Wang, Yujiao Zhu and Yan Lin for their contributions in field sampling. Funding for this study was provided by National Natural Science Foundation of China (41121004, 21190050), State Key Joint Laboratory of Environmental Simulation and Pollution Control (Peking University), and the National Science Foundation's CAREER Award under contract # 32525-A6010 AI.
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