Applicability of Vegetation to Reduce Traffic-Borne PM2.5 Concentration in Roadside User Zones in Hot Arid Climates: The Case of Central Doha, Qatar

Abstract

The ‘Beautification of Roads and Parks in Qatar’ is an urban development project that intends to provide space for exercising in roadside greenery in central Doha due to a lack of accessible open spaces. Considering the potential health risks associated with inhaling traffic-borne PM2.5, this study investigated the efficacy of four common road vegetation scenarios in reducing traffic-borne PM2.5 concentration in roadside user zones using ENVI-met. It examined Spearman’s rank correlation between air temperature, relative humidity, traffic emission rate, and PM2.5 concentration in roadside user zones. Based on the results, (1) hedgerows lower PM2.5 concentrations in roadside user zones, while trees significantly increase the concentration. (2) There is a strong association between air temperature and relative humidity and the PM2.5 concentration. The PM2.5 concentration decreases as air temperature increases but it increases as relative humidity increases. (3) There is a moderately negative association between the traffic emission rate and the PM2.5 concentration; however, this association is not found to be statistically significant. The ENVI-met simulation showed a slight overestimation of PM2.5 concentration compared to the wind tunnel simulation. These findings provide insight into planning road vegetation to reduce traffic-borne PM2.5 in roadside user zones in the local hot arid climate.