Observational Analysis of the Influence of Aerosol Radiation Effect on Planetary Boundary Layer Structure and Entrainment Characteristics

An unmanned aerial vehicle (UAV) equipped with portable instruments was used to measure the vertical profiles of temperature, specific humidity, and particulate matter under different haze-polluted weather conditions in Nanjing from December 22, 2017 to January 18, 2018. The study aimed to assess the impact of the aerosol radiative effect on the atmospheric boundary layer (ABL) and the entrainment zone structures as well as their evolution on days with heavy haze pollution and other days with good air quality. The vertical profiles of the potential temperature, water vapor, and PM_2.5 concentrations were obtained through detailed analyses of the UAV-measured vertical profiles and surface observations, including the surface heat flux, 2-m air temperature, specific humidity, wind speed, wind direction, and major air pollutants concentration (e.g., O₃ and PM_2.5) under different air pollution conditions. The results indicate that aerosols reduce the amount of surface-reaching solar radiation and the surface sensible heat flux, postpone the development of the ABL, enhance the atmospheric stability near the surface, decrease the ABL height, and exacerbate air pollution. The maximum concentrations of PM_2.5 and the largest increase rate were observed at the top of the ABL rather than near the surface. Furthermore, the aerosol radiative effect was found to have an important impact on entrainment and its characteristic parameters. The depth of the entrainment zone increased with increasing surface PM_2.5 concentrations. The entrainment rate normalized with convective velocity did not follow a negative?1 power function with the convective Richardson number under heavy haze or PM_2.5 pollution conditions, which is consistent with the findings of large-eddy simulation studies. These results indicate that the aerosol radiative effect must be included in ABL and entrainment parameterization schemes to improve numerical predictions of weather and air quality under heavy pollution conditions.