Variations in Nocturnal Residual Layer Height and Its Effects on Surface PM2.5 over Wuhan, China

Xin Ma,Boming Liu,Yingying Ma,Hui Li,Shikuan Jin,Wei Gong,Weicheng Jiang

doi:10.3390/rs13224717

Abstract

Large amounts of aerosols remain in the residual layer (RL) after sunset, which may be the source of the next day’s pollutants. However, the characteristics of the nocturnal residual layer height (RLH) and its effect on urban environment pollution are unknown. In this study, the characteristics of the RLH and its effect on fine particles with diameters <2.5 μm (PM2.5) were investigated using lidar data from January 2017 to December 2019. The results show that the RLH is highest in summer (1.55 ± 0.55 km), followed by spring (1.40 ± 0.58 km) and autumn (1.26 ± 0.47 km), and is lowest in winter (1.11 ± 0.44 km). The effect of surface meteorological factors on the RLH were also studied. The correlation coefficients (R) between the RLH and the temperature, relative humidity, wind speed, and pressure were 0.38, −0.18, 0.15, and −0.36, respectively. The results indicate that the surface meteorological parameters exhibit a slight correlation with the RLH, but the high relative humidity was accompanied by a low RLH and high PM2.5 concentrations. Finally, the influence of the RLH on PM2.5 was discussed under different aerosol-loading periods. The aerosol optical depth (AOD) was employed to represent the total amount of pollutants. The results show that the RLH has an effect on PM2.5 when the AOD is small but has almost no effect on PM2.5 when the AOD is high. In addition, the R between the nighttime mean RLH and the following daytime PM2.5 at low AOD is −0.49, suggesting that the RLH may affect the following daytime surface PM2.5. The results of this study have a guiding significance for understanding the interaction between aerosols and the boundary layer.

Highlights

The residual layer (RL) is a neutral layer suspended above the stable boundary layer (SBL) at night [1,2]
The SBL hinders the exchange of pollutants and energy between the surface and the free atmosphere; most of the energy and pollutants in the daytime mixing layer are retained in the RL [3]
residual layer height (RLH) are are analyzed analyzed based based on the hourly average data

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The residual layer (RL) is a neutral layer suspended above the stable boundary layer (SBL) at night [1,2]. The SBL hinders the exchange of pollutants and energy between the surface and the free atmosphere; most of the energy and pollutants in the daytime mixing layer are retained in the RL [3]. The RL can retain large amounts of aerosols, which may be the source of the day’s pollutants and may further affect the surface environment [4,5]

Methods

Results

Conclusion