Impact of volcanic emissions on the air quality during the 2021 volcanic eruption of Tajogaite, La Palma: Implications for population exposure to volcanic pollutants

Volcanic eruptions inject particles (tephra) and gases into the atmosphere, impacting air quality. To provide new insights into this process, we focus on the 3-month-long 2021 Tajogaite eruption, on La Palma in the Canary Islands, Spain. This eruption emplaced lava flows and produced tephra and gases in multiple sustained plumes. We examined the relationship between air quality, tephra dispersion and deposition, and eruption dynamics. We reconstructed the spatiotemporal variations in tephra deposition using a collection network deployed around the island and maintained throughout the eruption, while plume dispersion was tracked using satellite observations. These datasets were compared to the air quality monitoring data from the local regulatory network using time-series analyses. Our findings reveal distinct peaks in tephra deposition rates (a few g/m²/h 20 km away from the vent, up to more than 2000 g/m²/h at locations less than 3 km from the vent), related to both increased explosive activity at the volcanic vents and specific atmospheric conditions. We show that the fluctuations of tephra emission were the main driver of the particulate matter (PM) concentration variations, outweighing contributions from secondary aerosol formation through volcanic SO₂ conversion. We evidence spatial disparity in the impact on air quality, with the western half of La Palma island experiencing higher amplitude and more frequent pollution peaks than the eastern half. We demonstrate that even low-explosivity basaltic eruptions can significantly affect air quality by generating and dispersing fine PM and gases over wide areas. Moreover, elevated PM concentrations persist beyond the duration of intense tephra deposition episodes, thereby extending the period of population exposure. These results have important implications for understanding and mitigating human exposure to volcanic pollutants.