Decomposition of three aerosol components using lidar-derived depolarization ratios at two wavelengths

Abstract. In this study, we present a novel algorithm using the lidar-derived particle linear depolarization ratios measured at two wavelengths for the decomposition of three aerosol components, to retrieve aerosol-type-specific backscatter fractions. This extended methodology builds upon well-developed polarization-based algorithms, e.g., POLIPHON (POlarization LIdar PHOtometer Networking) method, offers an added advantage for an almost unambiguous separation of three aerosol components, on the condition that their characteristic depolarization ratios are different. And it requires the proper knowledge of characteristic depolarization ratio and the backscatter-related Ångström exponent of each aerosol type. The mathematical relationship between particle linear depolarization ratios at two wavelengths for a mixture of two aerosol components has been derived and expressed as an equation. This equation is visualized as a curved line, where the boundaries are determined by the characteristic depolarization ratios and the curvature is influenced by the characteristic backscatter-related Ångström exponents of both aerosol types. Moreover, the pair values of particle linear depolarization ratios of three aerosol components at two wavelengths must remain within the enclosed region predetermined by three boundary curves, and each curve is determined by the characteristics of any two of three types. Such characteristic curved relationships are more accurate than the common use of the ratio of the particle linear depolarization ratios. This novel algorithm has been applied to synthetic examples considering dust mixtures and to lidar observations of Arabian dust, Asian dust, and Saharan dust, so as to decompose coarse-mode dust (>1 μm in diameter), fine-mode dust (<1 μm in diameter), and spherical non-dust aerosols. The dust characteristics reported in numerous laboratory and field studies have been considered.