Optical Constants for Asian Dust in UV-VIS Region and OMI Observations

Optical constants for Asian dust are determined based on the compositions, such as clay minerals, quartz, feldspars, and calcite, reported in the literature for the spectral range of 0.2 - 1.0 μm. The imaginary part of refractive index for Asian dust is much smaller than the imaginary index of the mineral-transported dust (MITR) in OPAC throughout the range. Compared to the imaginary part of the optical constants for Saharan dust reported by Kandler et al. [2009] in UV region, the present value is significantly smaller. The effects of Asian dust are simulated using VLIDORT [Spurr et al., 2006] with a typical lognormal size distribution of the dust, and the results are compared with OMI observations. When calculated using the present optical constants, the normalized radiance increases with wavelength in the range of 0.35 - 0.5 μm as AOD at 0.5 μm increases. The normalized radiances of OMI observations for Asian dust events support the simulated results. They increase with wavelength as the dust loading increases, when compared with those for clean skies at the same locations. However, when simulated using the optical constants of MITR, the effects of dust tend to decrease the normalized radiance in the range of 0.35 - 0.5 μm, indicating that the present optical constants are better than those of MITR to access the Asian dust effects .