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Abstract

Chemistry modelling can be employed to study regional air quality and inform mitigation strategies. To accurately represent air quality, realistic emission data for all natural and anthropogenic sources need to be supplied. Volcanic emissions represent a significant challenge, due to their unpredictable nature. As a result, only a small number of volcanoes are included in emission datasets, focusing only SO₂, despite the potential release of micron-scale volcanic ash that can affect particulate matter (PM) concentrations. These emissions can be especially important in the case of volcanoes with long periods of passive emissions and intermittent eruptions, as in the case of Sakurajima volcano in southern Japan. Due to its high level of activity since 1955 and the large nearby population, Sakurajima is one of the most closely-monitored volcanoes in the world. The permanent deployment of equipment such as tiltmeters and tephra collectors has allowed for the accurate estimation of volcanic ash emissions, giving us the unique opportunity to provide realistic input data for air quality modelling. Emissions were simulated using two models: WRF-chem, a chemistry model, and FALL3D a volcanic emission transport model. Simulations are carried out for 2019, covering anthropogenic, biomass burning and non-volcanogenic natural emissions (WRF-chem) and volcanic emissions (FALL3D), with results validated against daily surface observations of airborne concentrations (PM and SO₂) and monthly ashfall values within the Kagoshima prefecture. Overall, results provide the first direct comparison of the ratio between volcanogenic and non-volcanogenic emissions and confirm the importance of the former.