Quantifying daily volcanic SO2 emissions on a global scale

The expression of volcanic activity at the Earth’s surface is accompanied by the emission of a cocktail of different gases, including water, carbon dioxide, sulphur species, halogens and metals. The composition and magnitude of these emissions reflects the state of magmatic systems, providing insights into volcanic processes and key hazard monitoring information. Many of these products also have serious health implications for local communities and are important species for the global climate. The primary target species for quantification of volcanic emissions is SO₂, due to its high prevalence in volcanic emissions, its low typical atmospheric concentration and the ability to detect it remotely using UV and IR spectroscopy from both ground and space.

Satellite instruments provide a global view of volcanic activity through a combination of geostationary and polar orbiting platforms. This is particularly useful for remote or difficult to reach volcanoes, as well as for identifying eruptions from those which have not been historically active. Most previous satellite work has focused on explosive eruptions due to the decreased sensitivity of satellites to SO₂ lower in the atmosphere, however recent advances in instrumentation and processing algorithms have opened the possibility of detecting and quantifying passive emissions in the troposphere.

In this work we combine daily SO₂ imagery from the TROPOMI satellite instrument with the PlumeTraj back-trajectory analysis toolkit to detect and quantify daily eruptive and non-eruptive SO₂ emissions as a function of time and altitude from volcanoes globally throughout the year 2020. We consistently detect more than 20 degassing volcanoes per day, dominated by non-eruptive emissions. We also investigate the emissions with respect to latitude, tectonic setting and volcano type.

These results demonstrate the ability of TROPOMI and PlumeTraj to provide daily automatic SO₂ emissions for volcanoes globally. In the future, this analysis will be extended to the full TROPOMI dataset (from 2018 to present) as well as to the development of a near real-time processing workflow. This will generate an invaluable dataset of volcanic degassing for investigating volcanic processes and characterising SO₂ emissions as a function of latitude and altitude, an important input for global climate modelling. Finally, the near real-time analysis will provide a key monitoring tool for volcano observatories worldwide.