Low-Level Jet (LLJ) is a vital meteorological phenomenon driving vertical air mass transport in the troposphere, yet its effects on near-surface ozone (O3) chemistry remain poorly understood. Based on comprehensive observations, this study investigates the seasonal influence of LLJs on surface O3 concentrations and associated photochemical mechanisms in Beijing. We find that LLJs consistently elevate nighttime O3 levels across all seasons by transporting O3-rich air from aloft. During daytime, however, their net effect on O3 varies seasonally, e.g., LLJs enhance O3 concentrations in spring and winter but suppress them in summer and autumn, as a result of a combination of both photochemical and physical processes. In summer, daytime surface O3 concentrations decrease on LLJ days due to the strong dilution/transportation effect, which outweighs enhanced photochemistry, where production rates of HO2, RO2, and O3 rise by approximately 47%, 71%, and 47%, respectively, due to lower NOx, higher JNO2, and elevated temperature. In winter, daytime O3 concentrations increase, driven by a higher O3 production rate (10 ± 36%) associated with elevated HO2 and RO2 production rates (38% and 32%, respectively), alongside high O3 concentration before sunrise and a comparable dilution effect on LLJ days compared to Non-LLJ days.
Wang et al. (Wed,) studied this question.