Dispersion of Volatile Hydrocarbons in Urban Street Canyons

Abstract

Volatile hydrocarbons (VHCs) were monitored in two urban street canyons for 16 days. Measurements of 15 selected VHCs were performed simultaneously at three different sampling heights: at street level (2 m), at 8 m, and at the rooftop (25 m above the ground). The aim of the study was to investigate the factors responsible for the horizontal and vertical changes in VHC concentrations. Physical parameters controlling the concentration gradients (wind flow and speed) were enabled. It was concluded that dilution and dispersion decrease the concentrations of HCs emitted at street level by approximately a factor of 6 between rooftop and street levels. Low winds and winds parallel to the street axis were identified as the worst dispersion conditions. The correlation between the measured VHC concentrations gave an insight into their fate. An empirical relationship between CO and benzene was established. These results may have important implications in planning monitoring studies to support research on population exposure in urban areas.