Estimates of pedestrian exposure to atmospheric pollution using high-resolution modelling in a real traffic hot-spot

Atmospheric pollution is a very relevant risk for the human health, in particular in urban environments, where most people lives and high levels of pollution are found. Population exposure is traditionally estimated through concentration recorded at air qualitymonitoring stations (AQMS) ormodelled at a spatial resolution of the order of 1 km(2). However, thesemethodologies have limitations in urban areaswhere strong gradients of concentration, even in the same street, exist. In addition, the movements of pedestrians make difficult to compute reliable estimates of pollutant concentration towhich people are exposed to. In this context, the main objective of this study is to estimate the exposure of pedestrians to ambient nitrogen oxides (NOx) concentrationswith high spatial resolution in a real urban traffic hot-spot under differentmethodologies. To achieve this objective, a novel methodologywhich combines high-resolution NOx concentrations from computational fluid dynamic (CFD) simulations with the pedestrian flows obtained by pedestrian mobility microsimulations is applied to an urban area of Madrid, Spain. High-resolution maps show pedestrian exposure peaks, at bus stops and crosswalks, that cannot be captured by the simpler methods based on spatial average concentration (SAC) or concentrationmeasured in an AQMS. Total daily exposure obtained is 1.19 center dot 109 person s mu g m(-3), while SAC and AQMS concentration methods yielded 9-23% and 30-40% lower values. In conclusion, the proposedmethodology allows to determine the areas with higher exposure in order to design local strategies to reduce the impact on human health. In addition, froma more general point of view, the total exposure in the studied area is better estimated by using spatial average concentration than through concentration recorded by AQMS. The assessment of the spatial representative of AQMS becomes necessary to use AQMS concentration to evaluate air quality and population exposure of an urban area. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study aims to estimate pedestrians' exposure to ambient nitrogen oxides (NOx) concentrations in a real urban traffic hot-spot using different methodologies. High-resolution maps reveal exposure peaks for pedestrians at bus stops and crosswalks, not captured by simpler methods based on spatial average concentration or measurements from air quality monitoring stations.