Optical Properties of North Atlantic Aerosols Through a compact dual-wavelength depolarization Lidar Observations

Abstract. We present a characterization of the optical properties of different aerosol types based on data collected using a compact dual-wavelength depolarization elastic lidar (532 and 808 nm, CIMEL CE376). We evaluate the vertical distribution and temporal evolution of a variety of aerosols observed in the subtropical North Atlantic region, covering from Saharan dust outbreaks and volcanic aerosols to fresh and aged wildfires, observed between August 2021 and August 2023, using a modified two-wavelength Klett inversion method to derive the aerosol backscatter and extinction coefficients from CE376 lidar observations. We assessed the performance of the CE376 lidar during an intercomparison campaign with an MPL-4B lidar (MPLNET) while collocated at the facilities of the Izaña Atmospheric Research Centre (Canary Islands, Spain). Both instruments depicted the vertical aerosol structure similarly. The main differences were attributed to errors arising from the determination of the overlap function and the depolarization calibration in each instrument and the larger effect of the solar background on the CE376 system during daylight. Absolute differences in the volume depolarization ratio (δ^v) were 0.3 % reduced to 0.2 % when only nighttime data was used. The measurements of particle linear depolarization (δ^P), extinction Ångström exponent (EAE (532/808)) and attenuated colour ratio (ACR (808-532)), provided by the combination of the two channels of the CE376, allow us to describe the composition and size of the studied aerosols. Fresh Saharan dust particles were the largest particles found in this study with non-spherical morphology and traveling in a well-mixed layer, exhibiting the lowest EAE (532/808) and highest ACR (808-532) and δ^P (532) > 0.15. The smaller particles with quasi homogeneous morphology were attributed to sulphate aerosol from the initial stage of the Cumbre Vieja volcano eruption and aged Canadian wildfires traveling across the Atlantic, showing the lowest δ^P (< 0.08) and the highest EAE (532/808) (>1). Middle values of these retrieved parameters were associated with the heterogenous mixture of ash, soot, and charred vegetation from fresh local forest wildfires. The retrieved properties demonstrate the excellent performance of the CE376 micro-lidar as a tool for continuous monitoring and characterisation of the temporal and vertical distribution of atmospheric aerosols.