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The inﬂuence of passenger activities on exposure to particles inside buses
W.W. Song, M.R. Ashmore*, A.C. Terry
Environment Department, University of York, Heslington, York YO10 5DD, UK
a r t i c l e i n f o
Articlehistory: Received 12 August 2008 Received in revised form 27 April 2009 Accepted 5 May 2009 Keywords: Bus Particulate matter Modeling Personal exposure Transport Box model
a b s t r a c t
Elevated personal exposures to particles have been reported in buses, but the factors associated with these high exposures are uncertain, and the potential role of passenger activities within buses has not beenquantiﬁed. To improve understanding of this factor we measured particle number concentrations in the range 0.3–15 mm simultaneously inside and outside buses in the city of York (UK), while carefully noting passenger activities. We also developed a box model to simulate the effects of passenger activities, and parameterised this from independent studies with controlled passenger activities. Thenumber concentrations inside buses were signiﬁcantly higher than those outside in all size classes, and the inside/outside ratios increased with particle size. The model showed broad agreement with measured particle concentrations inside buses, and demonstrated, for particles in the range 3–15 mm, that both re-suspension by passenger activities and deposition to the surface of the passengers hadsigniﬁcant effects on concentrations. Hence, understanding of the effects of passenger activities on both particle deposition and re-suspension is essential to interpret exposure measurements inside buses. Exposure of regular commuters inside buses could be of potential health signiﬁcance and needs further assessment. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Increased atmosphericconcentrations of particles are associated with increased morbidity and mortality (e.g. Pope, 2000; Sunyer, 2001; Koenig et al., 2005; WHO, 2006a). Epidemiological evidence summarized by WHO (2006b) suggests that about 350,000 premature deaths could be attributed to long-term exposure to particles in the 25 countries of the European Union in 2000, while short-term exposure to particles alsoincreases the risk of emergency hospital admissions for cardiovascular and respiratory diseases. An important issue for interpretation of these studies is how the outdoor concentrations used to deﬁne exposure in epidemiological studies relate to individual personal exposures to particles in different locations (Ashmore and Dimitroulopoulou, 2009). Individual personal exposures to particles are oftenhigher than indoor and outdoor concentrations due to the presence of a personal cloud (e.g. Wallace et al., 2006), while many studies (e.g. Pellizzari et al., 1993; Mohammadyan and Ashmore, 2005) indicate that outdoor concentrations are poor predictors of individual personal exposures to particles. Personal exposure to particles in transport has been investigated in various modes, including car,bus, train, taxi, and tram (e.g. Akbar and Ashmore, 1997; Adams et al., 2001; Chan et al., 2002;
* Corresponding author. Tel.: þ44 1904 434070. E-mail address: email@example.com (M.R. Ashmore). 1352-2310/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.05.004
Gulliver and Briggs, 2004). These studies indicate that exposure to particles in transportmicroenvironments is higher than in indoor locations and at urban monitoring sites, and also suggest that those travelling in buses may be exposed to relatively high particle concentrations (Gulliver and Briggs, 2004; Adams et al., 2001). The reasons for high exposure inside buses are not clear, but it is known that personal exposure to coarse particles in microenvironments with large numbers of...