Contents lists available at ScienceDirect Transportation Research Part D journal homepage: www.elsevier.com/locate/trd A novel approach for the modelling of air quality dynamics in underground railway stations E. Walther, M. Bogdan AREP, 16 avenue d’Ivry, 75013 Paris, France ARTICLE INFO Keywords: PM 10 Conservation model Underground air quality ABSTRACT Indoor air quality in subterranean train stations is a concern in many places around the globe. However, due to the specificity of each case, numerous parameters of the problem remain un- known, such as the braking discs particle emission rate, the ventilation rate of the station or the complete particle size distribution of the emitted particles. In this study the problem of modelling PM 10 concentration evolution in relation with train traffic is hence addressed with a particle- mass conservation model which parameters are fitted using a genetic algorithm. The parameters of the model allow to reproduce the dynamics and amplitude of four field data sets from the French and Swedish underground contexts and comply with realistic bounds in terms of emis- sions, deposition and ventilation rate. 1. Introduction Indoor air quality in subterranean railway station is an increasing public health concern. Numerous measurement campaigns and simulations have been undertaken worldwide, e.g. (Strak et al., 2011) in the Netherlands, (Ma et al., 2012) in Japan, in Korea (Park et al., 2012) or (Gómez-Perales et al., 2007) in Mexico City, as they help to understand the mechanisms that create such indoor/ outdoor pollution, with the aim to reduce it. However, these studies mainly measure pollution levels and provide design or operation guidelines without a quantitative analysis of the link between train traffic and particulate matter concentration. The clear weekly pattern of PM 10 concentration in subterranean railway stations and the similar behaviour of particle con- centration evolution and train movement frequency observed for instance in Gustafsson et al. (2012) as well as in the measurement data exhibited in Fig. 1, led us to investigate the modelling of this relationship. The difficulty of this enterprise resides in the unknowns around the two key phenomena: – the source of particles, divided in direct emission by abrasion and resuspension of deposited particles, is unsufficiently char- acterised, – the dilution mechanism, which in underground stations strongly depends on the piston effect and comfort ventilation. The piston effect is indeed responsible for sporadic, violent drafts in the tunnels (Cusáck et al., 2015) and complex, sometimes counter- intuitive, air flows on the platforms, with generated dynamic pressures reaching about thousand Pascal upon arrival in the station (Ke et al., 2002) and air velocities of about 1/5th of the train velocity (Brown, 1965). Different sources have shown that iron is the dominant element in underground stations (Jung et al., 2010). In the review by Qiao et al. (2015) of eight suburban stations over the globe, particle mass concentration in iron is superior by one order of magnitude to all other elements. Determining a value for the direct emission term, i.e. how many particles are emitted by the components of the trains http://dx.doi.org/10.1016/j.trd.2017.07.014 E-mail addresses: edouard.walther@arep.fr (E. Walther), mateusz.bogdan@arep.fr (M. Bogdan). Transportation Research Part D 56 (2017) 33–42 1361-9209/ © 2017 Elsevier Ltd. All rights reserved. MARK