*Article* **Changes in SO2 Flux Regime at Mt. Etna Captured by Automatically Processed Ultraviolet Camera Data**

**Dario Delle Donne 1,2,\*, Alessandro Aiuppa 1, Marcello Bitetto 1, Roberto D'Aleo 3, Mauro Coltelli 4, Diego Coppola 5, Emilio Pecora 4, Maurizio Ripepe <sup>6</sup> and Giancarlo Tamburello <sup>7</sup>**


Received: 9 April 2019; Accepted: 15 May 2019; Published: 20 May 2019

**Abstract:** We used a one-year long SO2 flux record, which was obtained using a novel algorithm for real-time automatic processing of ultraviolet (UV) camera data, to characterize changes in degassing dynamics at the Mt. Etna volcano in 2016. These SO2 flux records, when combined with independent thermal and seismic evidence, allowed for capturing switches in activity from paroxysmal explosive eruptions to quiescent degassing. We found SO2 fluxes 1.5–2 times higher than the 2016 average (1588 tons/day) during the Etna's May 16–25 eruptive paroxysmal activity, and mild but detectable SO2 flux increases more than one month before its onset. The SO2 flux typically peaked during a lava fountain. Here, the average SO2 degassing rate was ~158 kg/s, the peak emission was ~260 kg/s, and the total released SO2 mass was ~1700 tons (in 3 h on 18 May, 2016). Comparison between our data and prior (2014–2015) results revealed systematic SO2 emission patterns prior to, during, and after an Etna's paroxysmal phases, which allows us to tentatively identify thresholds between pre-eruptive, syn-eruptive, and post-eruptive degassing regimes.

**Keywords:** SO2 fluxes; UV Camera; Etna Volcano; explosive basaltic volcanism
