The influence of school bus ventilation scenarios over in-cabin PM number concentration and air exchange rates

Abstract School students are exposed to the increased particulate (PM) number concentration inside the school bus on daily basis while commuting on urban road networks. However, the potential effect of different ventilation over in-cabin pollutants is still unclear in many aspects. The present paper investigates the influence of varying ventilation scenarios over in-cabin particle number concentration (PNC) and air exchange rates (AERs) inside idle and moving (unoccupied (SBu) and occupied (SBo)) school bus. The in-cabin total PNC sharply increased by a factor of 1.53, 1.57 and 1.14 for SBp, SBu, and SBo respectively under windows open (WO) from windows closed (WC) scenarios. In-vehicle student activity and ventilation scenarios were positively correlated with the change in in-cabin PNC. For SBp, the average estimated AERs are 9.19 h−1 and 3.30 h−1 under WO and WC scenarios respectively whereas, total PNC deposition rate under natural convection condition varied between 2.52 and 6.88 h−1. In the present study, inside-outside measurements were recorded for 10 km long road segment under realistic driving conditions. The average AERs value of SBu and SBo are highest for WO (42.40 h−1 and 14.46 h−1) compared to WC (10.91 h−1 and 10.94 h−1). A Generalized estimating model (GEE) model was developed and the model suggested that vehicle age, mileage and speed are the factors positively associated with the AERs estimated for WO and WC scenarios under realistic driving conditions.