The vertical distribution of air pollutants in urban street canyons is closely related to residents' health. However, the vertical air quality in urban street canyons has rarely been assessed using field observations obtained throughout the year. Therefore, this study investigated the seasonal and annual concentrations of particulate matter (PM2.5 and PM10), CO, NO2, SO2, O3, air quality index, and their responses to microclimatic factors at three height levels (1.5, 27, and 69 m above street level) in an urban street canyon. The PM concentration was higher at 27 m than at 1.5 m in winter, whereas the situation was reversed in other seasons. It was found that photochemical pollutants such as NO2 and O3 were the primary pollutants in the urban street canyon. The days on which O3 was the primary pollutant at the height of 1.5 m accounted for 81.07% of the entire year. The days on which NO2 was the primary pollutant at the height of 27 and 69 m accounted for 82.49% and 72.33% of the entire year, respectively. Substantially higher concentrations of NO2 and O3 were found at the height of 27 m than at 69 m. In-canyon concentrations of NO2 and O3 were strongly correlated with air temperature, wind speed, and wind direction, which played important roles in photochemical reactions and pollutant dispersion.
Keywords: Built environment; Urban air pollution; Urban form; Urbanization.
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