Effects of aerosol vertical distribution on the intensity and polarization properties of twilight

The unique dynamics of rapidly changing atmospheric illumination altitude during the twilight period make its observations particularly sensitive to the vertical distribution of aerosols. A comprehensive investigation of aerosol vertical distribution's effects on twilight intensity and polarization is essential for developing robust algorithms to achieve quantitative aerosol retrieval. The effects of different aerosol vertical distributions (including exponential distributions with aerosol scale heights of 0.5, 1, 2, and 3 km, as well as uniform distribution in the troposphere and uniform distribution in the troposphere and stratosphere) on the twilight intensity <i>I</i> and the Stokes parameter <i>Q</i> for four typical aerosols (biomass burning aerosols, water-soluble aerosols, dust aerosols, and sea salt aerosols) were systematically analyzed in this study. The results indicate that the influences on <i>I</i> differ significantly between exponential and uniform (both tropospheric-uniform and tropospheric-stratospheric-uniform) vertical distributions. However, under exponential distributions, aerosol scale height variations from 0.5 to 3 km have a minimal effect on <i>I</i>. In contrast to <i>I</i>, <i>Q</i> exhibits high sensitivity to all types of aerosol vertical distributions and changes in aerosol scale height. Across different vertical distribution conditions, the maximum percentage deviation in <i>Q</i> can reach 92.29%, with that of <i>I</i> being only 14.64%, suggesting the potential utility of twilight polarization measurements in retrieving aerosol vertical distribution information. The simulated results generally show good consistency with the measurements taken by CE318-TP at Lingshan, Beijing. The results provide a theoretical basis for retrieving atmospheric aerosol properties at different altitudes based on twilight and also offer insights for the further improvement of twilight intensity and polarization simulations.