Investigating traffic-related PM exposure on and under pedestrian bridges: A case study in Xi'an, China

Abstract

We measured particulate matter concentrations (PMCs), including PM10, PM2.5, and PM1.0 fractions, on andunder pedestrian bridges over two different types of roads: an urban expressway and an arterial road. Theobjectives of the study were to 1) assess the variability of PMCs measured at pedestrian bridges, 2) identify bestfitprobability distribution curves of different measures of PMCs, and 3) quantify pedestrian exposure (by respiratorydeposition dose (RDD) rate). Results showed that the average on-bridge PM concentrations weresignificantly higher than the under-bridge values over the urban expressway, although no similar trend observedover the arterial road. More specifically, average PM1.0 concentration on the bridge was 1.29 times of that underthe bridge over the urban expressway. Gaussian distribution “best” fit the 30s average PMCs for PM10 on andunder the pedestrian bridge over the urban expressway, and LogNormal distribution “best” fit the PMCs for PM10on and under the bridge for the arterial road. The average RDD rates for PM10 (143.85 μg h−1), PM2.5(9.41 μg h−1), and PM1.0 (3.78 μg h−1) on the bridge over the urban expressway (OBUE) were higher by 47%,41%, and 11%, respectively, than those on the bridge over the arterial road (OBAR). While only minor differenceswere noticed in the average RDDs of PM between on and under the pedestrian bridge over the arterialroad, a significant difference in the average RDD rate was found between on and under pedestrian bridges overthe urban expressway.