Real-time measurements of CO2 and δ13C in volcanic gases emitted in atmosphere from Mt. Etna (Italy)

Abstract:

We present new data of real-time measurements of concentration and isotope (δ¹³C) composition of CO₂in fumarolic and plume gases emitted from Mt. Etna volcano, performed by using a Delta Ray tunable diode laser. The first two campaigns of measurements were carried out on 11 July and on 5-6 September 2013, while a third campaign was performed in mid-July 2014.

Data acquired along the route Catania–Etna, while car was moving, showed an excess of ¹³C-depleted CO₂ when passing through inhabited centers due to atmospheric pollution produced by the cars exhaust. A similar behavior was observed when accidentally measuring car exhaust of our car. Differently, volcanic gases displayed a ¹³C-enrichment of CO₂ if compared to air. With the assumption of a two components mixing, a simple linear regression was applied to the data in order to obtain the volcanogenic δ¹³C of CO₂.

Fumaroles of Torre del Filosofo (2,900 m a.s.l.) displayed a δ¹³C between -3.2±0.03‰ and -3.7±0.05‰, comparable to IRMS measurements of discrete samples collected in the same date and in previous investigations. Diluted plume gases were collected at more than 1 km from the craters and showed δ¹³C=-2.2±0.2‰, accordingly with collected crater fumaroles. Data collected in 2014 campaign are under processing, but preliminary results confirm a less negative signature of δ¹³C of CO₂emitted from Central Craters if compared to Torre del Filosofo fumaroles, with some interesting variations over time that need to be compared with other simultaneously acquired parameters.

Considering the huge amount of data that may be acquired in a very short time by Delta Ray, we demonstrate that the addition to the atmospheric CO₂ content of ~100 ppm of CO₂ from an unknown source is enough to allow a mathematical calculation of the end-member with an uncertainty generally < 0.15‰. This is feasible with the assumption of a binary mixing. We thus infer that these measurements performed at Mt. Etna, if performed continuously, may contribute to a better comprehension of the magmatic processes.