Spatial distribution of traffic air pollution and evaluation of transport vehicle emission dispersion in ambient air in urban areas

Vertical distribution of traffic-related pollutants inside an open street-canyon were observed in Suzhou, P.R. China, in 2005. The aim was to explore transfer and diffusion characteristics of vehicular exhaust emissions, as well as monitoring constraints associated with street canyons, courtyards and enclosed spaces. Vertical wind speed was found to strongly affect the fluctuation of all the pollutants. Daily average concentrations of NOx, NO2 and NO, as well as NO2/NOx ratio, were found to vary significantly alongside the vertical, proportionate to different average daily trends. Oxidation processes and photochemical activity are discussed to explain these phenomena. Daily CO trends were found to track closely with both NOx and Benzene, while the corresponding ratios were different relative to other published works. Different emission factors and driving conditions, as well as other emission sources types (especially for Benzene) are used to explain this point.