Aerosol optical properties retrieved from a prede sky radiometer over an urban site of Beijing, China

SKYNET is an international research network of ground-based Prede sky radiometers for the observation and monitoring of aerosol–cloud–radiation interactions in the atmosphere. The algorithm developed by SKYNET is SKYRAD.pack, which can be used to process the measurement data of Prede instruments. In this study, the latest SKYRAD.pack software (Version 5.0) has been used to retrieve the aerosol optical properties measured by a SKYNET Prede sky radiometer over an urban site of Beijing, China. Continuous data have been processed over a two-year period, and inversion products, including aerosol optical depth (AOD), Ångström exponent (α), volumes of different aerosol particle size distributions, and single-scattering albedos (SSA), have been analyzed. AOD values were found to vary from 0.11 (5th percentile) to 1.14 (95th percentile) with a median of 0.34 at 500 nm, and the maximum and minimum seasonal α values in Beijing were 1.05 ± 0.36 in summer and 0.82 ± 0.39 in spring. SSA values are higher in summer and spring with a similar value of 0.96 ± 0.03, but lower in winter with a value of 0.93 ± 0.04 at 500 nm. Aerosol particles in Beijing clearly demonstrated bimodal size distributions throughout the year: there were coarser particles in spring and finer particles in summer. The α values increased with AOD, indicating that fine particles play an important role in the optical properties of aerosols in Beijing. Dust type aerosol occurrence accounted for 4.1 %, 5.1 %, 0.5 %, and 1.2 % of all measurements data in spring, summer, autumn, and winter, respectively, according to the dust criteria threshold (α < 0.47 and SSA_400nm − SSA_{1020 nm} < 0.018).