Analysis of aerosol optical properties in a Lanzhou suburb of China

Abstract

In order to accurately identify feature layer and monitor the spatial and temporal distribution of pollutants, the inversion method of lidar measurement based on multiscale algorithm is proposed in this paper. The detection of clouds, aerosols and dust layers using a modified retrieval algorithm for a dual-wavelength lidar is presented at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). Moreover, the aerosol optical depth calculated from the Klett-Fernald algorithm obviously excludes the influence of clouds. Two cases were presented to demonstrate that the modified algorithm can capture low-clouds and dust layers well. The aerosol optical properties including aerosol optical depth (AOD), effective radius, depolarization ratio and black carbon aerosol mass concentration are analysed in terms of their monthly and seasonal variations. It is shown that the maximum of AOD, depolarization ratio and effective radius were found in spring (0.42 ± 0.35, 0.17 ± 0.1, 0.63 ± 0.24 μm) and the minimums were found in summer and autumn. The black carbon aerosol mass concentration varies significantly throughout year, with the maximum value in winter (2.35 ± 1.56 μg m−3) and a secondary maximum in autumn (1.93 ± 1.28 μg m−3), a minimum (1.03 ± 0.76 μg m−3) in spring. The vertical distribution of extinction coefficient has a peak near 1 km (0.1 km−1). The depolarization ratio vertically distributes at approximately 0.15. In general, pollution is more serious in spring and winter at SACOL, the former pollutants are coarse-mode non-spherical dust particles which originate from the Taklimakan Desert and the Gobi Desert, and the latter are fine mode spherical black carbon aerosols and coarse-mode non-spherical dust aerosols which are the results of both local combustion and long-distance transport. The dust particles existed high-altitude transport in spring and winter at SACOL.