Research Article Influence of Pedestrian Trajectories on School Children Exposure to PM 10 João Garcia, 1 Rita Cerdeira, 1 Luís Coelho, 1 Prashant Kumar, 2,3 and Maria da Graça Carvalho 4 1 Escola Superior de Tecnologia de Set´ ubal, Instituto Polit´ ecnico de Set´ ubal, Campus do IPS, 1910-761 Set´ ubal, Portugal 2 Department of Civil and Environmental Engineering, Faculty of Engineering and Physical Science (FEPS), University of Surrey, GU2 7XH, UK 3 Environmental Flow (EnFlo) Research Centre, FEPS, University of Surrey, GU2 7XH, UK 4 Instituto Superior T´ ecnico, Avenida Rovisco Pais 1, 1049-001 Lisboa, Portugal Correspondence should be addressed to Jo˜ ao Garcia; joao.garcia@estsetubal.ips.pt Received 31 March 2014; Revised 10 June 2014; Accepted 18 June 2014; Published 22 July 2014 Academic Editor: Godwin Ayoko Copyright © 2014 Jo˜ ao Garcia et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tree pedestrian trajectories are considered to study the infuence of PM 10 concentrations on children exposure, in a high-trafc street canyon. Two types of exposure were calculated: daily exposure for each wind condition and cumulative annual exposure considering all wind conditions. FLUENT was used to simulate the fow, turbulence, and PM 10 dispersion in the street canyon. Our results indicate that exposure is infuenced by the chosen walking trajectory and wind direction. When considering daily exposure, the highest value is achieved for the trajectory on the south side of the street, under westerly wind conditions, 13% higher than the baseline that assumes no trafc. Te results indicate that a particular trajectory can be better for one specifc wind direction but can represent the worst for a diferent wind direction. A diference of 3% to 13% higher exposure was achieved by choosing the best and worst trajectories. When computing cumulative annual exposure, trajectory on the north side of the street shows better results, 8.4% higher than the baseline value. Northerly and westerly winds result in the lowest and the highest exposure value for every studied trajectory. Careful selection of the best pedestrian paths can help reduce the exposure in busy street canyons. 1. Introduction Air quality in city environments is a matter of increasing interest due to its direct impact on the public health [1]. In the last decades, trafc-related air pollution and health problems have increased, especially in children during their scholar age [2]. Children’s bodies are still under development during this age, making their airways, alveoli, and immunity systems more vulnerable to diseases [3]. Furthermore, children inhale more air per kilogram of body weight than adults due to their increased breathing rates [4–6]. It is now accepted that air pollutants can trigger allergies and respiratory problems, particularly in children with chronic respiratory diseases [7]. However, this is a complex issue since it is not easy to confer causes to some respiratory diseases such as asthma and bronchitis due to the limited understanding on cellular and molecular levels. Tis issue is further complicated by the complex temporal and spatial pattern of human exposure to air pollution [8, 9]. Te fact that the intervenient factors can interact between themselves, the relation between pollutant concentrations and health is even more complex [10]. Long- term exposure to low level concentrations of air pollutants, sometimes even below legislation limits, can also have signif- icant health impacts [8]. Tese issues make the concentration of particulate matter (PM) in urban street canyons one of the major air pollution issues. PM is a complex mixture of solid and liquid particles that are made of organic and inorganic substances [11]. Numerous scientifc studies have correlated exposure to PM in air pollution, showing a number of health issues. Tese include increased respiratory problems, such as respiratory irritation, coughing, or difculty in breathing [10, 12], reduction of Hindawi Publishing Corporation Journal of Nanomaterials Volume 2014, Article ID 505649, 9 pages http://dx.doi.org/10.1155/2014/505649