Influential parameters on particle exposure of pedestrians in urban microenvironments

Exposure to particle concentrations in urban areas was evaluated in several studies since airborne particles are considered to bring about adverse health effects. Transportation modes and urban microenvironments account for the highest contributions to the overall daily particle exposure concentration. In the present study an evaluation of the influence parameters affecting particle exposure of pedestrian in urban areas is reported. Street geometry, traffic mode, wind speed and direction effects were analyzed through an experimental campaign performed in different streets of an Italian town. To this purpose a high-resolution time measurement apparatus was used in order to go after the dynamic of the freshly emitted particles. Number, surface area and mass concentrations and distributions were measured continuously along both the sides of street canyons and avenue canyons during 10-minutes walking routes. The combined effect of street geometry and wind direction may contribute strongly to dilute the fresh particles emitted by vehicles. In particular, street canyons are characterized by lower ventilation phenomena which lead to similar concentration values on both the side of the street. Higher wind speed was found to decrease concentrations in the canyon. Traffic mode also seems to influence exposure concentrations. In particular, submicrometer particle mass concentration was higher as the traffic is more congested; otherwise, coarse fraction dominates mass exposure concentration along street characterized by a more fluent traffic, showing a typical resuspension modality.