Atmospheric vertical structure variations during severe aerosol pollution events based on lidar observations

Abstract. During severe haze events, the boundary layer exhibits a complex vertical structure, while high aerosol loadings hinder high-resolution temperature and humidity measurements. To address this, a Raman-Mie lidar and retrieval algorithms for temperature, humidity, and aerosol optical properties were developed at Xi’an University of Technology, enabling high-resolution profiling of haze vertical structures. A 12-day haze episode was continuously monitored from formation to dissipation, providing detailed spatiotemporal variations of temperature, relative humidity, and aerosols. The boundaries of temperature inversion (TI) and aerosol layers were identified using a threshold method. The results revealed a strong coupling between aerosols and temperature during pollution evolution. Dome and stove effects were observed, with possible coexistence and interaction. Three dome-shaped TIs were identified. The top of a decreasing-type aerosol layer formed a stratified dome structure that constrained vertical diffusion, with the temperature gradient of the elevated TI varying inversely with its depth. Both TI strength and humidity were strongly correlated with surface PM_2.5 concentrations. Surface-based TI exhibited a clear diurnal variation, with TI peaks preceding aerosol peaks. The results indicated that strong elevated TI and weak turbulence in the lower layer favored aerosol accumulation. Clouds and virga not only suppressed radiative heating but also enhanced humidity, further driving the rapid increase in surface PM_2.5 concentrations. During the dissipation stage, the rapid breakdown of TI and enhanced solar heating were critical for pollutant removal, while efficient horizontal transport facilitated the complete clearance of aerosols within the boundary layer.