Vertical profile of polarization over Vladivostok using horizon shadowing: Clues to understanding the altitude variation of reflectance of aerosol particles

We report polarimetric measurements of atmospheric aerosol in evening and morning twilight over Vladivostok (Russia) in late winter-early spring of 2017 using a horizon-shadowing technique. Motion of the Sun beneath the horizon changes the altitude of the boundary of the shadowed atmosphere h, making it possible to constrain the altitude of aerosol particles contributing to the polarimetric response. We investigate the degree of linear polarization P in aerosol particles at different altitudes, ranging from 0 km up to 17 km. In two out of four experiments we found significant variations of the polarimetric response (Delta P similar to 10%) with altitude; whereas, in the other measurements, the polarization appeared nearly the same (Delta P similar to 2-3%) throughout the entire range of the studied altitude. Polarization P was measured in the zenith direction with the scattering angle being theta similar to 90 degrees At such a scattering angle, the polarization is near its maximum value P-max. We analyze our measurements using the Umov effect that describes an inverse correlation between P-max and the geometric albedo A. On 2017-02-21, we estimate A approximate to 0.0120 +/- 0.0004 at h=0 km and A approximate to 0.0154 +/- 0.0026 at h=10 km. On 2017-02-27, we find the opposite trend, A approximate to 0.0108 +/- 0.0003 (h=0 km) and A approximate to 0.0084 +/- 0.0006 (h=10 km). On 2017-03-02 and 2017-03-03 we find A as 0.0084 0.0009 and A approximate to 0.0090 +/- 0.0010, respectively. Conclusions drawn from polarimetric measurements appear in qualitative accordance with results of remote sensing with a three wavelength lidar. (C) 2017 Elsevier Ltd. All rights reserved.