Investigating the Geometrical and Optical Properties of the Persistent Stratospheric Aerosol Layer Observed over Thessaloniki, Greece, During 2019

Abstract

A persistent stratospheric layer first appeared during July 2019 above Thessaloniki, Greece (40.5°N, 22.9°E), initially at 12 km and during August 2019 even up to 20 km, with increased thickness and reduced attenuated backscatter levels. In this study, we analyze the geometrical and optical properties of this stratospheric layer, using both the ground-based multi-wavelength depolarization measurements performed with Thessaloniki’s lidar system (THELISYS), which is part of the European Aerosol Research Lidar NETwork (EARLINET) and the spaceborne lidar CALIOP retrievals (Cloud–Aerosol Lidar with Orthogonal Polarization), onboard CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation). The origin of the plume is linked with the two major sources of stratospheric air pollution that were active in the summer of 2019, the Raikoke volcano eruption in the Kuril Islands and the intense forest fires at mid and high northern latitudes. Thus, in July, pure volcanic sulfate aerosol layers (particle linear depolarization ratio < 0.05) are mainly identified in the stratosphere, while in August, wildfire smoke is dominating. Temporal changes in the aerosol properties throughout the 2019 measuring period that signify changes in the composition of the long-lasting stratospheric plume over Thessaloniki are identified and discussed.