Single-scattering albedo profiling of mixed Asian dust plumes with multiwavelength Raman lidar

Abstract

This study presents results of vertically-resolved single-scattering albedo of mixed Asian dust plumes, i.e. the total single-scattering albedo. The mixed Asian dust plumes are comprised of a mixture of pure dust particles and the non-dust part, e.g. urban/industrial pollution and smoke from biomass burning. The mixed Asian dust plumes were observed with multiwavelength Raman lidar which provides vertical profiles of particle backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm. The optical data serve as input for an inversion algorithm that provides profiles of microphysical particle properties which subsequently are used for computing single-scattering albedo. This study presents results of dust plumes observed on 24 February 2004, 9 and 18 March 2004, 2 April 2004, and 24 February and 4 May 2005. The lidar measurements were carried out at Gwangju (35.10° N, 126.53° E), South Korea. The optical data of the mixed-dust plumes were separated into the pure dust content and the non-dust part. We used the linear particle depolarization ratio measured at 532 nm for this separation. The backscatter and extinction coefficients then were used to derive single-scattering albedo of the non-dust part of the mixed-dust plumes. The value 0.96 ± 0.02 at 532 nm for the single-scattering albedo of pure dust part was used. This value was obtained from single-scattering albedo of dust observed in various dust source regions. In another step the “total” single-scattering albedo of these mixed-dust plumes was calculated by using the optical depth of the dust and the non-dust part as weighting function. The single-scattering albedo of the non-dust particles of the mixed-dust plume varied from 0.63 to 0.93 for all observations presented in this study. The single-scattering albedo of the mixed-dust plumes was 0.71–0.95, and it was always higher than the single-scattering albedo of the non-dust part of the mixed-dust plumes. Single-scattering albedo varied with height on each measurement day. These differences seem to be quantitatively related to the degree of mixing of dust with urban pollution and the light-absorption properties of the pollution (non-dust) particles in these plumes which traveled along different transport pathways to the lidar site. The layer-mean lidar-derived single-scattering albedos of the examples shown in this study were compared to single-scattering albedo derived from AERONET (Aerosol Robotic Network) Sun/sky radiometer observations. This radiometer is located next to the lidar. The total layer-mean lidar-derived single-scattering albedos (at 532 nm) on 18 March and 2 April 2004, and on 24 February and 4 May 2005 were 0.91 ± 0.02, 0.90 ± 0.03, 0.91 ± 0.02, and 0.92 ± 0.02, respectively. The lidar-derived single-scattering albedos are similar to those based on the Sun/sky radiometer data if the different measurement wavelengths of the lidar and Sun/sky radiometer are taken account of.