Sulfur Dioxide Flux Calculator

The "SO2 Flux Calculator" is an open-access web application provided within the framework of the Volcano Space Observatory Portal. The "SO2 Flux Calculator" computes daily-averaged sulfur dioxide (SO2) gas mass flux emitted from a volcano, using data derived from Sentinel-5P/TROPOMI Level-2 SO2 products.

The input data for the service is constituted of daily SO2 mass integrated over a series of nested circular domains centered on a given volcano. The input daily SO2 mass time-series can be computed directly from the web application or using the companion open-access VolcPlume platform (Boichu and Mathurin, 2022), after selection of the time period and volcano of interest.

Calculation is based on the "disk method" (Grandin et al., 2024). The approach consists in calculating a regression of the mass-to-distance distribution, including (a) a linear term proportional to the SO2 mass flux (proto-flux) and (b) a quadratic term proportional to the level of spatially-averaged noise in the input satellite images. The web application uses an algorithmic implementation of the "disk method" in Python language, available from https://git.icare.univ-lille.fr/icare-public/so2-flux-calculator.

After estimating the "proto-flux", the user may incorporate information on wind-speed, which converts the result into a daily-averaged SO2 mass flux. Wind speed can be defined manually, or, optionally, can be extracted from the wind fields of the ERA-5 reanalysis by choosing a custom altitude (among the 37 pressure levels of ERA-5). In addition, a statistical criterion is applied for automatic detection of degassing, using an adjustable confidence threshold.

Service is available here: [SO2 Flux Calculator](https://dataviz.icare.univ-lille.fr/so2-flux-calculator)

References

Boichu, M. and Mathurin, T. (2022). "VOLCPLUME, an interactive web portal for the multiscale analysis of volcanic plume physico-chemical properties". [Interactive Web based Ressource], AERIS. Platform access from https://volcplume.aeris-data.fr/ (homepage: https://www.icare.univ-lille.fr/volcplume/) doi: 10.25326/362, https://doi.org/10.25326/362

Grandin, R., Boichu, M., Mathurin, T. and Pascal, N. (2024). "Automatic estimation of daily volcanic sulfur dioxide gas flux from TROPOMI satellite observations: application to Etna and Piton de la Fournaise". Journal of Geophysical Research: Solid Earth, 129, e2024JB029309. https://doi.org/10.1029/2024JB029309