The 2021 paroxysmal events at Mt. Etna: Modelling of SO2 and volcanic ash dispersion by using WRF-Chem model

From 18 January to 23 October 2021, 58 paroxysmal events occurred at Mt. Etna volcano by the South East Crater (SEC). Three events, that occurred on 4, 12 March and 24 June, were selected to be studied through a plume dispersion modelling approach. All the selected paroxysms generated ash-SO₂ rich plumes ranging from 6 to 8.5 km above the main vent.
In this work, we explored the spatial dispersion of the volcanic SO₂ plume in each paroxysmal event by using the Weather Research and Forecasting Chemistry (WRF-Chem) model coupled with the time-variable ground-based SO₂ flux emission data recorded by FLAME (FLux Automatic MEausurement) scanning spectrometers network managed by INGV-OE (Osservatorio Etneo). In this context, WRF-Chem was specially configured to run with variable Eruption Source Parameters (ESPs), reading at each integration time-step experimentally measured SO₂ flux values.
The SO₂ maps resulting from the WRF-Chem simulations were compared with the dispersion pattern detected by TROPOMI sensor onboard Sentinel-5p satellite, in order to validate the capability of the model in reproducing the volcanic plume dispersion. The comparison for each simulation highlights a very good agreement between simulated data and those observed by the satellite.
The ash transport was also modelled in each simulation, considering an ash Mass Eruption Rate (MER) which was inverted from the plume height. The spatial evolution of the ash patterns was compared with data retrieved from the MGS-SEVIRI satellite. The comparison shows a good agreement between simulated and observed maps. Particularly for the 12 March event, the ash comparison clearly shows that the WRF-Chem model was able to well reproduce the eastward path of the ash cloud, even at long distances, as the simulated plume reached Greece about 10 hours after the paroxysm, in agreement with satellite observations.
In conclusion, the obtained results testify that the WRF-Chem model can efficiently reproduce the dispersion of both SO₂ and ash plume emitted from Mt. Etna volcano over the Mediterranean basin, representing a powerful tool for assessing air quality, flying security and other hazard factors due to volcanic plume transport and deposition from local to Mediterranean scale. In addition, the performed simulations highlighted that the ground-based data measured by the FLAME network play a key role in improving the accuracy in simulating the SO₂ dispersion pattern as it allows us to take into account the fluctuating and not stationary nature of volcanic plume emissions.