Seasonal and Diurnal Characteristics of the Vertical Profile of Aerosol Optical Properties in Urban Beijing, 2017-2021

Seasonal and diurnal characteristics of the vertical profiles of aerosol properties are essential for detecting the regional transport and the climatic radiative effects of aerosol particles. We have studied the seasonal and diurnal characteristics of the vertical distribution of aerosols in urban Beijing from 2017 to 2021 based on long-term Raman-Mie LiDAR observations. The influence of the vertical distribution of aerosols, the meteorological conditions within the boundary layer, the optical-radiometric properties of aerosols, and their interconnections, were investigated during a heavy haze pollution event in Beijing from 8 to 15 February 2020 using both meteorological and sun photometer data. The aerosol extinction coefficient was highest in summer (0.4 km(-1)), followed by winter (0.35 km(-1)), and roughly equal in spring and autumn (0.3 km(-1)). The aerosol extinction coefficient showed clear daily variations and was different in different seasons as a result of the variation in the height of the boundary layer. During the haze pollution event, the particulate matter mainly consisted of scattered spherical fine particles and the accumulation time of pollutants measured via the AOD(440nm) and PM2.5 mass concentration was different as a result of the hygroscopic growth of the aerosol particles. This growth increased scattering and led to an increase in the aerosol optical depth. The vertical transport of particulate matter also contributed to the increase in the aerosol optical depth.

Automated summary

The seasonal and diurnal characteristics of the vertical distribution of aerosols in urban Beijing from 2017 to 2021 were studied using long-term Raman-Mie LiDAR observations. The influence of aerosol vertical distribution, meteorological conditions within the boundary layer, optical-radiometric properties of aerosols, and their interconnections were investigated during a heavy haze pollution event in Beijing from 8 to 15 February 2020 using meteorological and sun photometer data. The aerosol extinction coefficient was highest in summer, followed by winter, and roughly equal in spring and autumn. During the haze pollution event, the particulate matter mainly consisted of scattered spherical fine particles, and the accumulation time of pollutants measured via AOD(440nm) and PM2.5 mass concentration was different due to the hygroscopic growth of the aerosol particles. This growth increased scattering and led to an increase in the aerosol optical depth. The vertical transport of particulate matter also contributed to the increase in the aerosol optical depth.