Numerical simulation of the effect of solar chimneys on NOx-O3 photochemical reaction and ventilation in urban street canyon

Abstract

The complex interaction between pollutants and insufficient ventilation in urban street canyon presents significant challenges to the creation of a healthy urban environment. This study proposed the innovative application of solar chimneys (SCs) to improve airflow structure and air quality in the confined space considering NO_x-O₃ photochemical reaction mechanism. The influences of ambient wind, solar radiation at three local solar times (LSTs), and the SCs on NO_x diffusion and ventilation performance in street canyon were revealed by developing a mathematical model. The results demonstrated that the uneven temperature distribution induced by solar radiation at the LSTs significantly influences both the NO_x-O₃ photochemical reaction and the airflow structure within the street canyon. The deleterious effects of thermal buoyancy on the airflow structure were mitigated by the integration of the SCs. The reaction shifted toward the conversion of NO₂ to NO as the temperature decreased. The integration of SCs resulted in a maximum temperature reduction of 6.01 K in the pedestrian respiratory zone and demonstrated maximum removal efficiencies of 66.12 % for NO and 70.65 % for NO₂. The NO_x levels on the leeward side initially increased and then decreased as the ambient wind strengthened, whereas the NO_x levels on the windward side consistently decreased. This research verifies the feasibility of utilizing the SCs to enhance the street canyon environments and offers a viable strategy for promoting healthy and sustainable urban.