TROPOMI enables high resolution SO2 flux observations from Mt. Etna, Italy, and beyond

The newly launched imaging spectrometer TROPOMI onboard the Sentinel-5 Precursor satellite provides atmospheric column measurements of sulfur dioxide (SO2) and other gases with a pixel resolution of 3.5 x 7 km(2). This permits mapping emission plumes from a vast number of natural and anthropogenic emitters with unprecedented sensitivity, revealing sources which were previously undetectable from space. Novel analysis using back-trajectory modelling of satellite-based SO2 columns allows calculation of SO2 flux time series, which would be of great utility and scientific interest if applied globally. Volcanic SO2 emission time series reflect magma dynamics and are used for risk assessment and calculation of the global volcanic CO2 gas flux. TROPOMI data make this flux time series reconstruction approach possible with unprecedented spatiotemporal resolution, but these new data must be tested and validated against ground-based observations. Mt. Etna (Italy) emits SO2 with fluxes ranging typically between 500 and 5000 t/day, measured automatically by the largest network of scanning UV spectrometers in the world, providing the ideal test-bed for this validation. A comparison of three SO2 flux datasets, TROPOMI (one month), ground-network (one month), and ground-traverse (two days) shows acceptable to excellent agreement for most days. The result demonstrates that reliable, nearly real-time, high temporal resolution SO2 flux time series from TROPOMI measurements are possible for Etna and, by extension, other volcanic and anthropogenic sources globally. This suggests that global automated real-time measurements of large numbers of degassing volcanoes world-wide are now possible, revolutionizing the quantity and quality of magmatic degassing data available and insights into volcanic processes to the volcanological community.