Role of Low-Level Jet Evolution in Vertical Aerosol Redistribution: A Doppler Wind Lidar Study Over East China

Abstract. Low-level jets (LLJs) significantly influence aerosol vertical transport and the resulting surface air quality. This study utilizes coherent Doppler wind lidar observations to characterize the impact of LLJ dynamics on vertical aerosol redistribution during two typical dust episodes over Hefei, East China. Results show that the vertical trajectory of the LLJ core is associated with dust transport through the combined effects of mechanical shear and thermal stability. In the April 2021 event, the northwesterly jet core exhibits a dynamic vertical evolution, descending from 2.5 km to 0.3 km before reascending to 1.0 km by the time of the surface PM₁₀ peak (410 μg m^-3). This movement maintains enhanced wind shear (> 0.04 s^-1) and associated mechanical turbulence at the jet's lower interface. Together, these processes are associated with the downward transport of dust into the surface layer through vertical coupling at the frontal leading edge. This corresponds to a surface PM₁₀ peak with little temporal delay relative to the onset of frontal influence. Conversely, the March 2022 event is characterized by a relatively stable LLJ core and a persistent capping inversion that acts as a structural barrier, maintaining the dust layer aloft. Persistent wind shear and turbulence below the jet core are associated with sustained elevated transport and temporary aerosol storage prior to the delayed surface response. This configuration decouples the LLJ from the surface, resulting in an approximately 8-hour phase lag between the onset of the surface frontal influence and the PM₁₀ peak (578 μg m^-3). The peak occurs during the transient breakdown of the capping inversion, coinciding with the downward redistribution of the elevated aerosol layer. Wind hodographs indicate that inertial oscillations contribute to the maintenance of these dust-laden LLJs following frictional decoupling. Overall, LLJ evolution is associated with either rapid downward redistribution or elevated storage with delayed surface release, depending on the jet height relative to boundary-layer stability. The results provide an observational basis for refining boundary-layer parameterizations in numerical weather prediction and air quality models.