Range-resolved retrieval of aerosol particle size distribution during Saharan dust intrusions over the Bavarian Alps using multiwavelength lidar observations

Abstract. We present ground-based remote sensing observations of Saharan dust over the Bavarian Alps during three events on 29 February, 29 March, and 29 April 2024, with emphasis on aerosol particle size distribution (APSD) retrieval from multiwavelength lidar measurements. Raman–depolarization lidar observations from Garmisch-Partenkirchen were combined with sun-photometer data from the summit of Zugspitze. Long-range transport from North Africa was confirmed using back-trajectory analysis and aerosol forecasts. Elevated dust layers extending up to 6–7 km a.s.l. were observed, frequently structured into multiple layers.

APSDs were retrieved by applying an inversion method that directly substitutes predefined (bi-modal log-normal) size distributions into the lidar equations, reducing the inversion to the estimation of a limited set of microphysical parameters. This approach enables range-resolved retrievals of effective particle radius, yielding values up to 3–4 µm within dust layers and decreasing with altitude. Comparison with column-integrated sun-photometer retrievals shows consistent coarse-mode effective radii (1.2–1.4 µm). The results highlight both the strengths and limitations of APSD retrieval from lidar, particularly regarding assumptions on particle shape and refractive index.