Aerosol radiative forcing over east Asia determined from ground-based solar radiation measurements

We developed a method of retrieving aerosol optical properties and their associated radiative forcing from simultaneously measured sky radiation and surface solar flux data. The method is then applied to data sets collected at Mandalgovi, Dunhuang, Yinchuan, and Sri-Samrong sites of the Skyradiometer Network (SKYNET), and at Anmyon, Gosan, and Amami-Oshima, to examine the aerosol characteristics of east Asia. From the analysis for the SKYNET sites it was found that aerosols in east Asia have smaller single scattering albedos (i.e., 0.89 for Asian dusts in Dunhuang, 0.9 for urban type aerosols in Yinchuan, and 0.88 for biomass burning aerosols in Sri-Samrong), compared to the single scattering albedo for the same type of aerosols found in other areas. Lower single scattering albedo suggests that the aerosols over east Asia absorb comparatively more solar radiation. The measurements taken during April at the latter three sites over the Korean peninsula and the East China Sea showed that the single scattering albedo of Asian dust becomes smaller during the course of its movement from the source region to east Asian seawaters (i.e., 0.86 at Anmyon, 0.84 at Gosan, and 0.80 in Amami-Oshima), compared with 0.89 found in the source region (i.e., Dunhuang). These findings strongly suggest that Asian dusts become blackened during the movement because of mixing with soot particles produced over the industrial/urban area of China. The overall atmospheric forcing efficiency (radiation flux per unit aerosol optical thickness at 0.5 mu m) of Asian dusts ranges from 65 to 94 W m(-2) near the east Asian seaboard area, indicating that atmospheric heating by Asian dusts can be significantly enhanced by the mixing with soot particles.