A Comparison of the Mineral Dust Absorptive Properties between Two Asian Dust Events

Asian dust events are generated by deep convection from strong low pressure systems that form over mineral dust source regions. This study compares the mineral dust optical properties of two strong Asian dust events from the winter (December 2007) and spring (March 2010) seasons using AERONET retrieved parameters from three sites along the dust event path: SACOL (dust source region), Xianghe (downwind mixed aerosol region), and Taihu (downwind pollution region). The parameters include: aerosol effective radius, optical depth (tau), absorptive optical depth (tau(abs)), their respective wavelength dependences or Angstrom exponents (alpha and alpha(abs)), and the spectral single scattering albedo (omega(o)(lambda)). The alpha(440-870) values in both cases do not exceed 0.62 indicating coarse mode particle dominance at all three sites. The winter case is shown to have carbonaceous influences at all three sites as given by alpha(abs440-870) between 1.3 and 1.8 with strong spectral tau(abs) absorption. The spring case is more dust dominant with alpha(abs440-870) of 1.7-2.5 (noting that the largest value occurred at Taihu) with strong tau(abs) absorption primarily in the visible wavelengths. Comparison studies between the observed and theoretically calculated omega(o)(lambda) for the winter and spring cases have shown an excellent agreement except for the winter case at Taihu due to pollution influences. The comparison studies also suggest that omega(o)(lambda) is more sensitive to particle absorptive properties rather than particle size. The sharp increase in the aerosol radiative effect (ARE) during the dust events with ARE(BOA) > ARE(TOA) suggests a stronger aerosol cooling effect at the surface than at the TOA.