New insights into the 2021 La Palma eruption degassing processes from direct-sun spectroscopic measurements

Abstract. During the 2021 La Palma eruption, both existing and newly deployed air quality and atmospheric monitoring networks in the Canary Islands (Spain) played a crucial role in supporting decision-making for public safety and enhancing the understanding of the crisis. In this study, we report direct-sun measurements using low (EM27/SUN) and high (IFS-125HR) spectral resolution Fourier Transform InfraRed (FTIR) spectrometers located up to ~140 km away from the volcano and contributing to key atmospheric global networks. In La Palma, the EM27/SUN was combined with a Differential Optical Absorption Spectroscopy (DOAS) instrument. We present new FTIR retrieval methods to derive the SO₂, CO₂, CO, HF, HCl relative abundance in the volcanic plume from both low- and high- resolution solar absorption spectra. We derived SO₂ volcanic emission fluxes from the Sentinel-5P TROPOspheric Monitoring Instrument (TROPOMI) and estimated the emission fluxes of the other volcanic species over the whole eruption. We estimate the volcanic emission to the atmosphere for SO₂, CO₂, HCl, HF and CO to be 1.8±0.2 Mt, 19.4±1.8 Mt, 0.05±0.01 Mt, 0.013±0.002 Mt and 0.123±0.005 Mt, respectively. We show a good agreement between these estimates and the degassing balance derived from a petrologic approach. This eruption produced emissions that compare directly with annual anthropogenic emissions at different spatial scales. This study demonstrates the feasibility of using existing atmospheric FTIR and DOAS global networks to monitor volcanic plumes composition more than 100 km away, and is of relevance for volcanological monitoring and research during volcanic crises.