Analysis of the Near-road Fine Particulate Exposure to Pedestrians at Varying Heights

ABSTRACT Scientific literature has overlooked how PM2.5 concentrations vary with varying pedestrian heights near a roadway. Understanding this is important because walking is an essential commuting element of a sustainable transportation system, and pedestrians’ height varies widely. Therefore, the focus of the current study is to bridge this gap using results from CALINE 4 model and mobile PM2.5 measurements. In CALINE 4, a simple pedestrian pathway depicting the selected study site located near the Sardar Patel Road, Chennai, India, was simulated. The PM2.5 concentrations were estimated on this pathway at varying heights (0.1–1.8 m) in 135 simulated runs. Subsequently, the sensitivity of the PM2.5 exposure difference across heights was explored with varying ambient PM2.5 concentrations, wind speed, traffic volume, and traffic compositions. Results indicated that the PM2.5 concentrations reduced with increasing heights of pedestrians in all the modelled runs. When this PM2.5 exposure difference was investigated with varying surrounding conditions, it was found that the difference in PM2.5 exposure across heights was influenced by the wind speed, traffic volume, and traffic composition. Ambient PM2.5 concentrations had no discernible effect on it. Car-dominated traffic with a higher mode share of heavy commercial vehicles was marked with the highest PM2.5 exposure difference across heights. For traffic volume, it was observed that for every 100 vehicles hr-1 increase in traffic volume, the PM2.5 exposure difference increased by 0.13 µg m-3 m-1 in the range of pedestrian’s height. For wind speed, calculations suggested that for every 1 m s-1 increase in wind speed, the PM2.5 exposure difference was reduced by 0.095 µg m-3 m-1 in the range of pedestrian’s height. Finally, to bolster the modelling results, mobile PM2.5 measurements (using portable, low-cost optical particle sensors) were conducted near a busy urban roadway at two different heights, 80 cm and 150 cm, during peak and off-peak hours. The results of mobile measurements were found to be consistent with CALINE 4 modelled results.