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 (τ), absorptive optical depth (τabs), their respective wavelength dependences or Angstrom exponents (α and αabs), and the spectral single scattering albedo (ωo(λ)). The α440–870 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 αabs440–870 between 1.3 and 1.8 with strong spectral τabs absorption. The spring case is more dust dominant with αabs440–870 of 1.7–2.5 (noting that the largest value occurred at Taihu) with strong τabs absorption primarily in the visible wavelengths. Comparison studies between the observed and theoretically calculated ωo(λ) 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 ωo(λ) 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 AREBOA > ARETOA suggests a stronger aerosol cooling effect at the surface than at the TOA. OPEN ACCESS Atmosphere 2013, 4 2