NASA - National Aeronautics and Space Administration

A vector radiative transfer model was used in conjunction with the line-by-line radiative transfer model and the database of high-resolution transmission (HITRAN) molecular absorption to simulate the degree of linear polarization of skylight in cloud-free conditions. Differences between simulated and measured polarization data in highspectral resolution are found to be within 1% after aerosol scattering and gas absorptions are carefully considered. Limiting experiments are conducted at wavelengths around 0.760 – 0.765 mm O2-A absorption band for the same columnar aerosol optical thickness but different aerosol profiles. Results showed that the degree of linear polarization of skylight at surface varies strongly and is sensitive to the vertical change of tropospheric aerosol mass (or extinction) as the wavelengths approach to the edge of O2-A absorption band. However, such sensitivity is minimal at all wavelengths when the aerosol composition or single scattering properties are vertically homogeneous. This study suggests that the polarization data can be used together with radiance data to constrain the simulation of vertical distribution of aerosol composition in chemistry transport models.