The characteristics and sources of the aerosols within the nocturnal residual layer over Wuhan, China

Abstract

The aerosols accumulating in the surface layer are an important factor in the study of urban environment pollution. In this study, the characteristics and sources of the aerosols within the nocturnal residual layer were investigated based on lidar measurements from May 2015 to July 2016. The results revealed that the annual average aerosol optical depths (AODs) in the residual layer (RL) and the stable boundary layer (SBL) were 0.2 ± 0.16 and 0.17 ± 0.11, respectively. The aerosol loading in the RL was higher than that in the SBL, accounting for 43% of the total surface aerosols. The AOD in the RL during the summer was the highest (0.32 ± 0.14), followed by autumn (0.24 ± 0.16) and spring (0.2 ± 0.16), and was the lowest in winter (0.11 ± 0.07). Moreover, the effects of different layer heights and meteorological parameters at different heights were investigated. The AOD in the RL was positively correlated with the residual layer height (RLH) and residual layer depth (RLD), with a correlation coefficient (R2) of approximately 0.58 and 0.58, respectively. The correlation coefficient between AOD in the RL and relative humidity at the heights of 0.4, 0.7, 1, and 1.3 km was 0.52, 0.52, 0.49, and 0.53, respectively. These results indicated that RLD and humidity would promote aerosol loading in the RL. The air mass potential source contribution function maps s revealed that the aerosols in the RL during spring and autumn originate from local and nearby areas, while the air masses during summer come from the local anthropogenic emission regions. In winter, the air masses that reach Wuhan often originate from the northwestern dust source region via long-distance advection. These findings are significant in the quest to improve our understanding of the effects of aerosols on environmental pollution.