Analysis of the long-range transport of the volcanic plume from the 2021 Tajogaite/Cumbre Vieja eruption to Europe using TROPOMI and ground-based measurements

Abstract. The eruptions of the Tajogaite volcano on the western flank of the Cumbre Vieja ridge on the island of La Palma between September and December 2021 released large amounts of ash and SO₂. Transport and dispersion of the volcanic emissions were monitored by ground-based stations and satellite instruments alike. In particular, the spectrometric fluorescence and Raman lidar RAMSES at the Lindenberg Meteorological Observatory measured the plume of the strongest Tajogaite eruption of 22–23 September 2021 over northeastern Germany four days later. This study provides an analysis of SO₂ vertical column density (VCD) and layer height (LH) measurements of the volcanic plume obtained with Sentinel-5 Precursor/TROPOMI, which are compared to the observations at several stations across the Canary Islands. Furthermore, a new modeling approach based on TROPOMI SO₂ VCD measurements and the HYSPLIT trajectory and dispersion model was developed which confirmed the link between Tajogaite eruptions and Lindenberg measurements. Modeled mean emission height at the volcanic vent is in excellent agreement with co-located TROPOMI SO₂ LH and local lidar ash height measurements. Finally, a comprehensive discussion of the RAMSES measurements is presented. A new retrieval approach has been developed to estimate the microphysical properties of the volcanic aerosol. For the first time, an optical particle model is utilized that assumes an irregular, non-spheroidal shape of the aerosol particles. According to the analysis, the volcanic aerosol consisted solely of fine-mode inorganic, solid and irregularly shaped particles – the presence of large aerosol particles or wildfire aerosols could be excluded. The particles likely had an isometric to slightly plate-like shape with an effective half of particle maximum dimension around 0.1 μm and a refractive index of about 1.51. Moreover, mass column values between 70 and 110 mg m^-2, mean mass concentrations of 45–70 μg m^-3, and mean mass conversion factors between 0.21 and 0.33 g m^-2 at 355 nm were retrieved. Possibly RAMSES observed, at least in part, volcanic secondary sulfate aerosol which was produced by gas-phase homogeneous reactions during the transport of the air masses from La Palma to Lindenberg.