Impacts of Atmospheric Boundary Layer Vertical Structure on Haze Pollution Observed by Tethered Balloon and Lidar

In this paper, the characteristics of the atmospheric boundary layer (ABL) vertical structure over the North China Plain (NCP) during a comprehensive observation experiment conducted during 15–21 December 2018 were investigated. Observational data were obtained with a large tethered balloon, Doppler wind lidar, and ground-level instruments. The maximum concentration of PM_2.5 exceeded 200 μg m⁻³, and the ratio of PM_2.5/PM₁₀ was approximately 0.4 (its maxi-mum was approximately 0.8) during the whole observation period, indicating the explosive growth of dominant fine-mode aerosols in the winter heating season. Elevated concentrations of pollutants decreased the solar irradiance received by the ground, resulting in lower temperature at ground level. Our results illustrate three distinct types of vertical profiles: Type 1 (convective state)—the concentration of PM_2.5 decreased nearly linearly with increase of the height below approximately 600 m; Type 2 (stable state)—the PM_2.5 concentration sharply decreased from the ground to approximately 200 m; and Type 3 (multilayer structure)—some pollutants were suspended aloft in the upper air layer. Diurnal evolution of the vertical profiles of PM_2.5 and their relationship with the changes in meteorological factors were identified. From daytime to nighttime, the vertical profiles evolved from Type 1 to Type 2 or Type 3. All the 33 vertical PM_2.5 profiles that we obtained showed a strong relationship with elements of the ABL structure, such as the distributions of winds, the inversion layer, and turbulence activities. A light-wind layer and weak turbulence activity, especially within the inversion layer, contributed greatly to the accumulation of pollutants. Vertical PM_2.5 concentration patterns were also greatly affected by local ground-level emission sources and regional transport processes.