Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv Analysis of exposure to fine particulate matter using passive data from public transport Benjamín Trewhela a,b , Nicolás Huneeus b,c,* , Marcela Munizaga a,b , Andrea Mazzeo b,1 , Laurent Menut d , Sylvain Mailler d , Myrto Valari d , Cesar Ordoñez b,2 a Departamento de Ingeniería Civil, División Transporte, Facultad de Ciencias Físicas y Matemáticas - Universidad de Chile, Santiago, Chile b Center for Climate and Resilience Research (CR)2, Santiago, Chile c Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas - Universidad de Chile, Santiago, Chile d Laboratoire de Météorologie Dynamique, CNRS, Ecole Polytechnique, IPSL Research University, Ecole Normale Supérieure, Université Paris-Saclay, Sorbonne Université, École des Ponts parisTech, Paris, France ARTICLE INFO Keywords: Air quality Exposure Mobility PM 2.5 Public transport users ABSTRACT The city of Santiago experiences extreme pollution events during winter due to particulate matter and the associated health impact depends on the exposure to this pollutant, particularly to PM 2.5 . We present and apply a method that estimates the exposure of users of the public transport system of Santiago by combining smart card mobility data with measured surface concentrations from the monitoring network of Santiago and simulated concentrations by the CHIMERE model. The method was applied between July 20th and 24th of 2015 to 105,588 users corresponding to 12% of the frequent users of the public transport system and approximately 2% of the total population of Santiago. During those five days, estimated exposure based on measured concentrations varied between 44 and 75 μg/m 3 while exposure based on simulated concentrations varied between 45 and 89 μg/m 3 . Furthermore, including socioeconomic conditions suggests an inverse relationship between exposure and income when measured concentrations are used, i.e. the lower the income the higher the exposure, whereas no such relationship is observed when using simulated concentrations. Although only exposure to PM 2.5 was considered in this study, the method can also be applied to estimate exposure to other urban pollutant such as ozone. 1. Introduction Air quality (AQ) levels are a societal concern in Santiago, Chile. During winter periods, particulate matter (PM) concentrations, more specifically fine PM (PM 2.5 ), exceed daily average thresholds set by Chilean environmental regulation potentially causing harm to human health and impacting the ecosystem (World Health Organization and UNAIDS, 2006). PM causes damage to the respiratory and cardiovas- cular system, leading to a higher number of hospital consultations, less productivity and premature death (Kim et al., 2015). The health impact of air pollutants in general, and PM in particular, depends on the exposure to a given pollutant. The personal exposure can be defined as the real exposure as it is experienced by individuals (Dons et al., 2011) and is usually calculated as the average of the concentration at the different places (micro-environments) visited by an individual weighted by the time spent at each place. Therefore, esti- mating the exposure of an individual requires knowledge of the pollu- tant concentrations along his/her trajectory and the time spent during the corresponding activity. An accurate exposure estimate takes into account indoor and outdoor air pollution. However, exposure and/or health impact has been estimated using solely outdoor concentrations (e.g. Anenberg et al., 2012). Concentration of air pollutants can be measured through portable instruments (e.g. Etyemezian et al., 2005; Deville Cavellin et al., 2015) or stationary air quality monitoring stations (e.g. Escudero et al., 2007; Azmi et al., 2010; Mavroidis and Ilia, 2012). In addition, it can also be estimated through chemical transport models (e.g. Draxler and Hess, 1998; Brasseur et al., 1998; Byun and Schere, 2006; Menut et al., 2013), https://doi.org/10.1016/j.atmosenv.2019.116878 Received 8 March 2019; Received in revised form 18 June 2019; Accepted 31 July 2019 * Corresponding author. Departamento de Geofísica, Facultad de Ciencias Físicas y Matemáticas - Universidad de Chile, Santiago, Chile. E-mail address: nhuneeus@dgf.uchile.cl (N. Huneeus). 1 now at School of Engineering - Department of Civil Engineering, University of Birmingham, Birmingham, UK. 2 now at Aquatic Physics Group, Department F.-A. Forel for Environmental and Aquatic Sciences (DEFSE), Faculty of Science, University of Geneva, Geneva, Switzerland. Atmospheric Environment 215 (2019) 116878 Available online 01 August 2019 1352-2310/ © 2019 Elsevier Ltd. All rights reserved. T