O3–NOx–VOCs photochemical pollutant dispersion in 2D street canyon under effects of solar radiation

Abstract

Solar radiation is a significant factor affecting the concentration and dispersion patterns of photochemical pollutants in urban environments. This impact is mediated through alterations in temperature and thermally-driven airflow patterns, but the full extent of these effects has not yet been quantified. To address this gap, ANSYS Fluent and APFoam were used to simulate the dispersion of photochemical pollutants in a 2D street canyon (aspect ratio = 1), incorporating the complex O₃-NO_x-VOCs chemical mechanism via the CS07 mechanism to accurately represent the chemical processes. The novelty lies in its comprehensive assessment of how solar radiation, emissions, and dynamic and chemical processes interact to affect photochemical pollution. It was found that under different radiation conditions, NO_x and O₃ concentrations exhibit distinct distribution patterns. Compared to the neutral condition, the decreased NO_x concentrations (23%) and increased O₃ concentrations (8.7%) are observed in the morning and at noon, whereas in the afternoon, NO_x concentrations rises (111%) and O₃ concentrations decreases (20%) in the canyon. At night, NO_x accumulates at the bottom of the windward side. Through sensitivity tests, we found that the primary pathway through which solar radiation affects the dispersion of photochemical pollutants is dynamic process. The pedestrian health risks of photochemical pollutants were evaluated that NO₂ health risks are more pronounced in the afternoon and at night, while O₃ risks are more severe in the morning and at noon. Overall, this study quantitatively demonstrates the significant impact of solar radiation on the photochemical pollutants and identifies the pathways of influence.