Abstract
Abstract. The aerosol–planetary boundary layer (PBL) interaction was proposed as an important mechanism to stabilize the atmosphere and exacerbate surface air pollution. Despite the tremendous progress made in understanding this process, its magnitude and significance still have large uncertainties and vary largely with aerosol distribution and meteorological conditions. In this study, we focus on the role of aerosol vertical distribution in thermodynamic stability and PBL development by jointly using micropulse lidar, sun photometer, and radiosonde measurements taken in Beijing. Despite the complexity of aerosol vertical distributions, cloud-free aerosol structures can be largely classified into three types: well-mixed, decreasing with height, and inverse structures. The aerosol–PBL relationship and diurnal cycles of the PBL height and PM2.5 associated with these different aerosol vertical structures show distinct characteristics. The vertical distribution of aerosol radiative forcing differs drastically among the three types, with strong heating in the lower, middle, and upper PBL, respectively. Such a discrepancy in the heating rate affects the atmospheric buoyancy and stability differently in the three distinct aerosol structures. Absorbing aerosols have a weaker effect of stabilizing the lower atmosphere under the decreasing structure than under the inverse structure. As a result, the aerosol–PBL interaction can be strengthened by the inverse aerosol structure and can be potentially neutralized by the decreasing structure. Moreover, aerosols can both enhance and suppress PBL stability, leading to both positive and negative feedback loops. This study attempts to improve our understanding of the aerosol–PBL interaction, showing the importance of the observational constraint of aerosol vertical distribution for simulating this interaction and consequent feedbacks.
Highlights
Aerosols have a critical impact on the earth’s climate through aerosol–cloud interactions (ACIs) and aerosol–radiation interactions (ARIs)
By altering the adiabatic heating rate of the atmosphere, the aerosol vertical distribution is of great importance to the planetary boundary layer (PBL)
A decreasing structure indicates a peak in aerosol extinction coefficient (AEC) near the surface, and the inverse structure indicates a peak in AEC in the middle or upper PBL
Summary
Aerosols have a critical impact on the earth’s climate through aerosol–cloud interactions (ACIs) and aerosol–radiation interactions (ARIs). A more stable atmosphere and lower PBLH will, in turn, increase the surface aerosol loading, which is the well-established positive feedback loop in the aerosol–PBL interaction Ample observational datasets for Beijing are available, including aerosol vertical distributions derived from lidar, optical properties derived from the sun photometer, profiles of meteorological variables from radiosonde (RS), and surface PM2.5 and meteorological parameters Based on these measurements, a radiative transfer model is used to simulate the vertical profiles of aerosol radiative forcing that are employed to investigate the impact of aerosols on buoyancy in the lower atmosphere.
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