Climatology of aerosol radiative properties in northern China

The climatology of aerosol radiative properties in northern China was examined from the ground-based solar and sky radiance measurements of six sites during 2001–2005. Compared with the scattering, the absorption ability of particles became relatively more remarkable in dusty days than in clear days over dust source and downwind regions. The aerosol optical thickness (AOT) of coarse particle (r > 0.6 μm) absorption accounted for about 82.0% of that of total particles at 440, 670, 870 and 1020 nm over dust source regions, and 61.1% over downwind regions in winter and spring. According to extinction AOT, the corresponding percentages of coarse particles were 63.6% of total particle at the four wavelengths over dust source regions, and 37.7% over downwind regions in winter and spring. The single scattering albedo (SSA) showed a low sensitivity to AOT at the four wavelengths over both source and downwind regions, about 0.94 for fine particles (r < 0.6 μm) and 0.85 for coarse particles in winter and spring, and 0.86 for fine particles and 0.73 for coarse particles in summer and autumn. The asymmetry factor also showed a low sensitivity to AOT at the four wavelengths in all seasons, about 0.58 for fine particles and 0.79 for coarse particles over source and downwind regions. The scattering phase functions of coarse particles at forward and backward angles were commonly larger than those of fine particles, with the minimum at 120° and 130° over source and downwind regions respectively.