Characteristics of Planetary Boundary Layer Height (PBLH) over Shenzhen, China: Retrieval Methods and Air Pollution Conditions

Abstract

What are the main findings? The gradient method and standard deviation method based on Micro-Pulse Lidar and the parcel method based on Microwave Radiometers are more sensitive to abrupt changes in boundary layer height. During the observation period, Shenzhen’s PBLH characteristics exhibited significant diurnal variation and high sensitivity to pollution, the daytime mean PBLH ranged from approximately 512 to 1345 m, while nighttime values generally decreased to around 500 to 650 m. And under high aerosol loading conditions, PBLH was significantly suppressed to approximately 500 m, indicating that pollution limits atmospheric mixing by inhibiting boundary layer development. What are the implications of the main findings? By comparing different retrieval methods, we can identify the strengths and weaknesses of each method, providing guidance on selecting appropriate algorithm for similar urban environments. The study of boundary layer characteristics in Shenzhen holds significant scientific value for future research on factors influencing boundary layer height in megacities. Highlights: The PBLH affects the intensity of the surface turbulence and the state of pollutant dispersion. Current research on PBLH characteristics and their relationship with pollution in coastal megacities remains insufficient. Moreover, existing studies rarely evaluate the consistency of various boundary layer solution methods, making it difficult to identify deviations in single methods. So, we conducted enhanced observation experiments in Shenzhen, a megacity in China, between March and July 2023. The characteristics of the PBLH was analyzed by five months of observations from Micro-Pulse Lidar (MPL) and Microwave Radiometer (MWR). Five retrieval methods (Parcel, GRA, STD, WCT, and Theta) were applied for comparative assessment. The results shows that all methods captured similar diurnal patterns. During daytime, the PBLH ranged from 512 to 1345 m, with Theta yielding the highest and STD the lowest average values. At night, PBLH decreased overall, and method-dependent differences persisted. Under different pollution levels, this study also discussion the properties of PBLH using MPL and microwave radiometer. And aerosol optical depth (AOD) and PBLH showed a strong negative correlation, indicating aerosol-induced suppression of boundary layer growth. The study of boundary layer characteristics in coastal megacities can provide reference for atmospheric physics research in economically developed coastal areas.